Do heat pumps work in cold climates? | Hacker News Reader

Do heat pumps work in cold climates?

carbonswitch.com

149 pointstejohnso326 comments

The heat pump I have installed reaches 1:1 at -20C, i.e. at that point there's no gain. But a) it rarely gets that cold around here, and at -10C it works fine - there was a dramatic (seriously dramatic) drop in amount of electricity I used during winter compared to before installation, and b) My heat pump was installed in 2010, since then they've only got more efficient and 1:1 is somewhere around -30C (or was, a couple of years ago when I last checked).

And what it does when it's really cold _and_ somewhat humid outside is that it detects when frost appear on the outside element, at that point it reverses the flow and uses the heat from inside to defrost the outside element. As far as I know it does not include any actual resistive heater for this (though I won't bet my life on that statement). It's been working very reliably all these years (except for a leak in the cooling fluid which appeared relatively soon after installation, promptly fixed by the provider). I have to get it cleaned now and then to keep up the efficiency. It's in every other respect completely without hassle.

EditAdd: The Japanese heat pumps sold in the coldest areas are "Nordic" models. They are extremely efficient. But in Japan, where they're made, you can't get them. Or at least, we could only find less efficient models. But I haven't been to Hokkaido yet, I'll have a look in the stores there to see if they have them there.

Is that "no gain" in terms of energy (i.e. heat energy out = electricity in), or financial (i.e. cost of electricity consumed by heat pump = cost of equivalent gas-fired system)?

EDIT: or is it "well-to-wheels" style energy (i.e. primary energy consumed by heat pump = primary energy consumed by gas boiler), or is it CO2 (same emissions)

With a 1:1 ratio it's heat energy out = electricity in, minus a small amount of efficiency loss (any heat produced on an external heater)

As to cost wise it depends on the cost per kWh of your electricity vs gas. In the UK gas is far cheaper per kWh.

CO2 wise it depends on the CO2 intensity of your electric source vs a local gas burner.

However that only applies when it's -20C. When it's a more reasonable like now at 7AM in Chicago when it's 2 degrees C, you're generating something like 2.5kWh of heat for every 1kWh of electricity. That may not be financially beneficial if your gas is 5c/kWh and electricity is 30c/kWh, that depends on your various deals.

For me in the UK, my external oil boiler this winter has cost about 10p/kWh. My electricity is 21p/kWh. A heat pump I looked at was a 3.84 ratio, so if that ratio held down as far as typical winter temperatures of 6C (it's currently 11C), that would be 5.5p/kWh, and obviously far less CO2 per unit of heat.

Last time I checked, replacing an existing gas installation with a heat pump in the UK just wasn't economically sensible.

Air source heat pumps were barely breaking even compared to gas so you'd be spending £10k+ to install it without saving any money.

Ground source heat pumps offered better efficiency but if I recall correctly purchase + installation was a £35k investment that would take decades to recoup.

There's also the consideration of additional costs due to lower running temperature which often necessitate larger radiators.

They might make more financial sense if energy costs stay high, since they're easier to supplement with domestic renewables.

Is that £10k for a mini split system? I'm not sure how many homes would need to spend that much. The UK is full of small flats and 2 up/down places that could rely on maybe one or two splits, Google shows that a decent setup would be about £2k plus installation (two splits each at £1k inc tax).

Given the hot summers and energy costs in the UK I think many homes would find that investment a net gain.

> There's also the consideration of additional costs due to lower running temperature which often necessitate larger radiators.

I don't know what that means. There are no radiators for mini splits or air source heat pumps, maybe you are talking about ground source hot-water systems? They are still stupidly expensive, for good reason, huge install consideration.

Today's low upfront cost of mini split heat pumps makes for a highly favourable option for new builds, and indeed even the average home.

> Is that £10k for a mini split system?

It was 2021 when I last last looked into it but I recall that 10k was the list price of the cheapest air source heat pump that wouldn't result in a net increase in energy bills. I don't believe it included installation or any other associated costs.

> Given the hot summers and energy costs in the UK I think many homes would find that investment a net gain.

It's almost unheard of for UK homes to have any sort of cooling installed.

> I don't know what that means. There are no radiators for mini splits or air source heat pumps, maybe you are talking about ground source hot-water systems? They are still stupidly expensive, for good reason, huge install consideration.

UK homes are mainly heated with hot water radiators in each room; typically by an on demand gas combi-boiler that also handles hot water. Heat pump installations in the UK typically heat a hot water tank[0] that provides domestic hot water and heats the radiators.

Due to poor insulation the gas central heating systems typically run at around 60-80c. Heat pumps here usually heat the water to around 40c. This will often require replacing existing radiators that were installed expecting ~70c flow temperature with oner that can disperse more heat into the room. It can also involve additional insulation.

> Today's low upfront cost of mini split heat pumps makes for a highly favourable option for new builds, and indeed even the average home.

Indeed, heat pumps are a sensible choice for most new build homes in the UK as well. They typically have much better insulation and are therefore less affected by the low flow temperature. The costs involved in retrofitting anything older than 10, maybe 20 years old were.

[0] https://solarthermuk.co.uk/wp-content/uploads/2020/12/air_so...

If you are looking at air to water heat pumps you will certainly be looking at much more expensive installs. Mini splits are way cheaper and don't require hooking up to the gas hot water system which can simply be retired to backup heat source.

And yeah, cooling is not a thing in the UK, my point is folks are definitely going to be looking toward that given the summers people have been having, increase heating costs will make mini splits a double win. No brainer to me and I bet mini splits will be in limited supply this summer in Europe.

I'm not sure how they'd work to be honest. The doubts I have about them:

* How would the heat be moved around the house?

* Obtaining permission to modify the exterior of a multi-occupancy dwelling is extremely difficult.

* You'd still require a source of hot water, reducing the already small savings over an efficient combi-boiler.

Based on the estimated savings of the Energy Saving Trust, it'd take around 26 years to pay off a £3k install that replaces a modern combi-boiler[0] and that's without the cost of using electricity to provide heated water. As recently as March of this year Which claimed most houses would have paid an extra £80/year if running a heat pump[1].

They could be a good choice for completely new installs and people stuck on resistive electric heating if they can find a way to disperse the heat evenly. I'd bet a lot of money that the majority of properties with electric heating are rentals, good luck convincing a landlord to pay for anything.

[0] https://energysavingtrust.org.uk/advice/air-source-heat-pump...

[1] https://www.which.co.uk/reviews/ground-and-air-source-heat-p...

Goes to show the huge differences in different countries for energy costs. Our electricity is $0.11kw/h and natural gas is $0.08 so with 300% efficiency vs. gas air furnace which is probably 50% efficient (so much heat gets lost in leaky ducting). Our heat pumps will have paid for themselves in ~5 years conservatively, and we also get to cool the house which we could not do before.

Moving the heat around the house requires doors to be open and thoughtful placement of the head units which have fans in them to push the air around. It is certainly not ideal but we are comfortable.

There was an article the other week:

https://news.ycombinator.com/item?id=34233719

Obviously it depends on ability to scale, but UK rad heating systems are usually rated for 50 or 60C, thus this seems to fit the bill.

Cool! I hope I didn't come across as hating the technology. In a perfect world I hope we'd be using geothermal district heating but while we're still installing units in individual homes I think heat pumps are currently the best way forward. The economics of retrofitting many standard homes simply don't really line up in many cases. Prior to the current energy crisis they were generally more costly than using gas and even after they only really make economic sense for the relatively small number of people stuck on electric heating[0].

Home renewables help but require even more capital investment, often taking 10 or more years to pay off. It doesn't help that where I am solar has extremely limited output in the winter. Domestic wind turbines are difficult to situate and get planning approval for. My cursory impression is that they're also less economical than many solar installs.

I've got some roof repairs coming up soon and I'm hoping the economics of replacing the existing roof with some nice looking solar slate tiles work out favourably!

[0] https://www.statista.com/statistics/426988/united-kingdom-uk...

The only heating around here these days is electrical (edit: except for wood stoves, which are usually allowed). Oil isn't allowed, and gas heating doesn't exist. So yes, "no gain" means that the heat output is equivalent to the electricity input (at the low turning point, which is around -20C for my pump - I should qualify that though, it used to be when it was new, but the tech who checked my pump a couple of years ago said it had lost some of its efficiency due to various things including some difficult to remove grime inside, but there still was no point in actually replacing it).

Of course, there's also the installation costs of a heat pump. But it did pay for itself in a reasonably short time. If it hadn't been that efficient it wouldn't have - first, there's the actual price, which is not as much these days as it used to be, but then there's the actual installation by a pro, and I believe that part has only gone up since then.

Small installations are pretty simple if you can run the electric yourself. Then just hire an HVAC tech to purge the lines and fill to manufacturer specs. Done. Complex installs with multiple head units per outdoor unit get complicated as you have maximum and minimum line lengths and the length of installed line impacts amount of refrigerant needed and such, takes a good bit of planning and knowledge.

This is a good point. And I'd imagine most people when talking anecdotally on their own experience are comparing based on cost. And of course costs will vary.

For instance we have a heat pump that we mostly use for AC. Our primary heat is a gas boiler feeding steam radiators. We'll use the heat pump in the shoulder seasons when you just want to take the chill out of a specific room, but usually nothing else heat wise.

Last winter our boiler died and we spent about a month without it. That provided me a good opportunity to do something closer to apples/apples. Despite having the cold weather rated heat pump (Mitsubishi HyperHeat2) the extra electricity consumed that month was about the same as our typical gas cost. A slight bit more actually.

But I have no idea about energy usage in an objective sense. And if I really wanted to go down this rabbit hole, we're subscribed to an energy plan that's mostly based on renewables whereas obviously 0% of our gas is the same.

I think almost matching gas energy costs implies dramatically lower total energy used and the benefits of being able to use renewables. Natural gas can only really win in terms of heating because producing heat is easier than producing electricity with the same gas

Quite possible.

In our case it is academic as due to quirks of our house configuration (the joys of a house pushing 200 years old) we can only get units in a couple of rooms. It's good enough to keep the house cool in the summer, and heat the house in a real emergency like last winter but not something we can rely on for primary heat.

> at -10C it works fine - there was a dramatic (seriously dramatic) drop in amount of electricity I used during winter compared to before installation

Were you heating with electricity before? In that case you're sure so see improvement since resistive heating is always 1:1 while your heatpump is 1:1 in some of the worst cases.

Yes it was mostly heating with electricity, though I used a wood stove as well, but that's difficult to use efficiently - so it didn't help as much as I thought it would (w.r.t. saving electricity). No gas or oil. The only change was to install the heat pump, and boom - electricity usage way down. Now the biggest user is hot water (hot water tank for showers and washing). I save money by showering at the gym.. I still have the electric heaters installed in my living room - they haven't been used a single time since 2010. As they're permanent installations I haven't got them removed, or I would have.

> I still have the electric heaters installed in my living room - they haven't been used a single time since 2010. As they're permanent installations I haven't got them removed, or I would have. That sounds great. And sorry if I go off topic but I'm curious how you "distribute" the heat throughout the house. Air vents? Underfloor heating? If you kept the old radiators I assume you picked an option that caused the least disturbance in the home yet is still efficient enough that you didn't need extra heating in a decade.

I haven't needed extra heating in a decade in the area where the heat pump is - I should have been more accurate. In other posts I added that I do have (ordinary) electric heating elsewhere, the main place these days is my home office (without that there wouldn't be much extra heating). Most of the other rooms are unheated or nearly so (100W-130W w/thermostat is way more than enough), they stay warm enough due to good insulation and some air flow in the house. Bedrooms don't need to be particularly warm, unheated is ok, and the basement (hall, storage rooms, etc) is fine at around 11-13C which it normally stays at even at the coldest time of winter (and fortunately not much more in the summer either - that part of the house is partly below ground and is an excellent stable cool environment).

Heat pumps come in two main flavors. They can be like a forced air system, where they heat/cool air in an air handler and blow warm/cool air all over the house. Or they can be ductless heat pumps, where there is a head unit inside the house that uses coolant lines to move heat back and forth between the exterior unit. The head unit blows warm/cool air, but they can only blow so far. You can add multiple head units and get extra zones, but that can get more expensive

As an aside, there are some things that you can do with having the air vents in the rooms and a forced air system with some control so that instead of "control baffles in the basement that lead to ductwork for one zone" it is instead "control baffles in rooms".

One such example: https://flair.co/pages/central-systems-smart-vents

You may be covering it with your second definition, but I'm not sure - there's also the option available in Ireland (and UK and elsewhere) of a wet heat pump. By that, I mean an air-source (or ground heat extracting) heat pump that connects to the existing wet radiator infrastructure of the house. Replaces a gas boiler, which is normal here.

I had to think a bit about the "wet radiator" and then realized we're talking about potentially older houses that circulate hot water to metal radiators in the house.

In that case, yea, it would be a {something} to water heat pump to heat up the water, and then circulate that water through the house.

It would be curious if there were installations that did the other way too. In theory, you could also circulate cold water in the summer. The problem would have been "how do you make the water cold?" and in many older cases, that would be impractical. Though... that could lead to condensation on the radiators in the summer which could have downstream effects (condensation drips water on the floor).

Not even older, it's a standard heating technique in the UK and Ireland, even in modern homes built last year. You can use an air-to-water heat pump to retrofit a condensing gas boiler. Some even come integrated in to the hot water storage tank - https://rointe.ie/electric-water-heaters/heat-pumps/

Theoretically you could indeed drive cool water to the radiators to cool the house, but you don't get the convection effect that a radiator produces when hot, nor thermal radiation. So you need to rely on transfer of heat from the air to the metal of the radiator, potentially with no airflow. Easier to open the windows. In the last 12 years, I've never wished I had a system to chill the air in my dwelling; Ireland is generally on the cool side (though this may change).

It's a curious thought of "could you close a room and point a fan at it and noticeably cool off a room?"

This would be kind of running a mini-split AC to the rooms using water as the refrigerant instead of what hvac normally runs.

It's not a "this is the best choice" or even "this is a better choice than opening the windows" but rather a "if you did this, would it work? kind of?"

> In theory, you could also circulate cold water in the summer

Yes, but it isn't very common at all for one simple reason: condensation. You have to keep the temperature of the coolant above the dew point, which requires knowledge of ambient temperature and humidity. That means your coolant isn't actually that cold, so it can absorb less heat before needing to be re-chilled. It's overall pretty inefficient.

To be clear: "zero heat gain" isn't the right threshold to think about unless your house is a closed thermodynamic system. Real houses lose heat in proportion to the temperature delta between inside and outside air. So what you really want to know is the temperature at which the heat pump is no longer capable of maintaining that delta. That's a whole lot higher than -20C.

FWIW: we installed a heat pump recently here in Portland, and conveniently had a once-in-a-decade cold snap (17-20F for 3 days -- the PNW isn't that cold) in its second month. The system was just-barely-heat-flow-positive. A six hour power outage dropped the house temperature to ~64F, and it took a good 30 hours to get back to the 69F set point of the thermostat.

So... on the whole we're pleased and the system did just fine in extremis. But no way would it handle -20C/-4F.

This is extremely dependent on the efficiency of your system and how well it is designed. A 15 SEER heat pump can't compare to a 21 SEER (all else equal).

There are heat pumps that do well below freezing, they're just top of the line and so more expensive.

What heat pump model did you install?

This is just a matter of pump size. People in colder climates size their pumps larger in expectation of these cold temperatures.

Of course, and on home insulation state. I'm just pointing out that the threshold to look at during isn't the one described. The specific numbers were just to illustrate the principle.

Neither is the one you are proposing since "big enough system to heat a house at cold temperatures" is just a question about what size of system to install.

The 1:1 threshold tells you about the temp that everyone needs to start thinking about alternative heat sources. If you system is undersized and/or your house is poorly insulated, that threshold may be higher, but those numbers are per installation and don't answer the broad question about if heat pumps can "work" in cold climates.

This kind of nitpicky debate gets so tiresome. Look, upthread comment implied pretty clearly that a particular heat pump as installed would "work" until zero net energy flow at "-20C". And I thought that was misleading, because that's not the threshold you use to size a heat pump as is doesn't reflect a steady state (at that temperature your home will be inexorably losing heat). And as I happen to have had personal experience in the recent past with measuring exactly this threshold on a newly installed heat pump, I thought people might be interested.

I'm deeply sorry if this offended you for some reason, but I still don't see how you're disagreeing with anything I wrote.

> Look, upthread comment implied pretty clearly that a particular heat pump as installed would "work" until zero net energy flow at "-20C"

I did not read it that way at all. To me they are clearly talking about the point at which your heat pump no longer provides a efficiency gain over a purely resistive heater.

I think where you went wrong is reading "gain" as "heat gain" rather than "efficiency gain". While the usage of "gain" is sort of ambiguous there, the rest of the comment thread makes it clear that the term 1:1 is not discussing the point at which your heat pump stops producing any heat but the point at which it becomes inefficient.

> that's not the threshold you use to size a heat pump as is doesn't reflect a steady state

I don't think anyone except you was talking about sizing the system, but about selecting the system type given the climate.

If you had come into this just saying "here's my relevant experience with sizing heat pumps", that would have been productive. However you strongly asserted that the OP was using the wrong metric, which they weren't.

> I'm deeply sorry if this offended you for some reason,

I'm not sure why you think I am offended.

I thought the comment was useful. I think for those that don't know the basis for the tech, they can read described temps as absolute values. I've seen people misunderstand thermoelectric heater/coolers (Peltier coolers) for similar reasons -- the tech can achieve a temperature differential rather than an absolute temperature as some people expect when comparing to traditional compressor-based fridges.

Relative and Absolute temps can generally mess people up too.

From the book Humble Pi by Matt Parker:

"In September 2016 the BBC news reported that both the US and China had signed up to the Paris Agreement on climate change, summarizing the agreement like this: "countries agreed to cut emissions enough to keep the global average rise in temperatures below 2°C (36°F)." The mistake here is not just that the BBC is still giving temperatures in Fahrenheit but that a change of 2°C is not the same as a change of 36°F, even though a temperature of 2°C is the same as 36°F. If you were outside on a day when the temperature was 2°C and you looked at a Fahrenheit thermometer, it would indeed read 36°F. But if the temperature then increased by 2°C, it would go up only by 3.6°F. The crazy thing is, the BBC initially got it correct. Thanks to the amazing website newssniffer.co.uk, which automatically tracks all changes in online news articles, we can see the chaos in the BBC newsroom as a series of numerical edits. To be fair, the article was part of the live coverage of breaking news and was designed to be regularly updated. The first version of the article that mentioned temperature gave the change as 2°C."

(https://books.google.ca/books?id=2IeVDwAAQBAJ&lpg=PT223&ots=...)

A modern heat pump designed for colder regions is reasonably efficient even at -25C, as in being able to output more than half of its maximum heat and still be far enough away from its 1:1 point to make it efficient (compared to resistive heating). So, still very useful as long as that particular output is sufficient to keep your home warm or at least just require a bit of additional heating, and that it's not that cold all the time. Obviously before investing in any type of heat pump one has to consider the nominal temperature range during winter in the area where you live. Even though I'm very happy with the performance of my comparably old heat pump there are definitely regions in my country where it would be less useful.

> People in colder climates size their pumps larger in expectation of these cold temperatures.

Both over- and undersizing them each have their own issues; see §2.1.1 and §2.1.2:

* https://yukon.ca/sites/yukon.ca/files/emr/emr-air-source-hea...

That's not a flaw in heat pumps, that's just the sizing of the system.

A good designer will not oversize HVAC for edge cases like a once-a-decade weather system. You will size it to meet typical conditions, saving money and increasing efficiency by having a 4 ton heat pump vs 6.

For heating conditions, the typical workaround to meet demand in edge case extreme or long term cold is to add resistive heat pumps, which are much cheaper than upsizing the whole system. Though they are less efficient and therefore cost more to operate, they will only be used a few days a year when the heat pump loses ground.

I have a 60kBtu/h ground-source heat pump backed up by 7kW heat strips that replaced a 110kBtu/h gas furnace. The heat pump meets our needs for probably 51 weeks a year. Typically we will have the strips kick on during a few days in February. But it saves us a ton of money not having to have a second heat pump or larger ground loop system.

> That's not a flaw in heat pumps, that's just the sizing of the system.

No, it's not. The temperature at which the heat pump produces zero net energy flow is a thermodynamic property of the system. You can make the system as big as you want and it will still produce zero energy, because zero times anything is still zero. That's why that temperature isn't interesting: yes, your heat pump "won't work" below that temperature, but it also "won't work" at a range of higher temperatures. And that range, as you point out, depends on installation details and insulation. But that's not what the upthread comment was saying.

And as it happens, I got a chance to measure that for my system. And it turns out to be somewhere around 15-17F. I genuinely thought folks would like to hear about that as useful info, but instead it turned into this giant "actually" subthread...

It sounds like you are claiming that a heat pump cannot be sized to meet the kW requirements of a given structure. It might not always be the wisest economic decision, but you can certainly install a larger capacity heat pump to meet whatever kW rating you would get from a given furnace. Consider the large systems used on office buildings or datacenters which greatly exceed the capacity needed for a normal home.

It is true that a given insulated structure will have heat loss varying based on the differential between indoor and outdoor conditions. This is a power curve, i.e. a certain kW rate of energy loss for given conditions. The rate will increase as inside and outside conditions diverge. But for anticipated conditions, it is a finite value you can use to plan your system.

This is what people mean is "just sizing": Install a system with a sufficient kW output rating to support your desired indoor and outdoor operating conditions. You would size it to exceed the real loss rate of the structure, so that you have head room to increase the differential within an acceptable recovery period.

GP's "zero gain" was a statement about efficiency, not heat loss. ("Zero gain in efficiency as compared to resistive heating" rather than "zero gain in net BTUs inside the house".)

I'm in the Portland area and got a heat pump installed in 2021.

I overbought for sure, as I got a hybrid system that has a gas furnace backup. I've never needed it, but I've had a couple times where I wanted it and it was nice to have. If I switch it from "Heat" to "Emergency Heat", then it overrides the automatic determination of which heat source to use and just uses gas.

I didn't lose power during that cold snap, but if I did, it would have probably brought the temp back up in under 4 hours.

We have quite a few power outages, so the best thing about gas furnace backup for me is that I only need a generator large enough to run the furnace fan to get heat in a power outage. Without it, I have to run a heat pump compressor and that is a lot more power than a fan.

Air-water heat pump provides heating for our house (170 m2, Estonia, well insulated) all year round without engaging support electric heaters. In fact, breaker for support heater is always off. Temperature went to -22C previous winter for couple of days, heat pump was able to handle it. Average winter temperature is about -4C.

This and other comments here are very useful for me. Been thinking of getting a heat pump for the areas of the house that aren't reached by the pellet stove. It regularly gets to -20C here but not usually for very long so I think we'd be fine. Also we could use it for cooling for the few weeks a year when it's 30C+.

Here we ofter have summer temps around +30C and winter -20C, in both I am very happy to have our heat pump. Our unit is operational down to -25C but for the handful of weeks where it does get that low we do run the gas furnace a little just to top up.

We installed three mini splits in total for a ~2k sq ft 1800s draughty home. Before we had them our central air gas furnace, which is ~20 years old, would burn through upwards of $600 a month of gas in winter. With heat pumps we pay $180 a month equalized and we run heat or cool all year except for maybe a month in spring and fall where it's perfect 22c outside.

Without this magical tech we'd be broke or cold in the winter and uncomfortable all summer.

Were you able to install it with your existing furnace or did you have to replace the furnace?

They mention mini splits, which could very well be installed in addition to or even in lieu of a traditional central HVAC.

Ductless mini splits are perfect for your use case.

I’m not fan of a heating technology that only fails when I need it most. The system can work adequately thousands of times, but I only get to freeze to death once.

Winter Storm Elliott dropped temperatures far below the average lows in places that might otherwise be well served by heat pumps. Many southern states saw -5 F and it got considerably colder elsewhere.

That’s not to say that heat pumps can’t play a role in HVAC systems, but they must have a backup.

It's not that the heat pump fails when it's < 20C, it's just that you don't get any additional efficiency versus heating directly with electricity.

Heat pumps are specified with significant margin and/or backup heat sources.

The numbers above are the 1:1 point, which doesn’t mean it stops working. It just means it’s similar efficiency to an electric heater at that point.

“Freeze to death” is an extreme exaggeration.

This is spot on. Some mini split heat pumps effectively become base board heaters with a fan when their efficiency falls off. You'll be uncomfortable, but you won't freeze to death.

You always need a backup heat source in cold climates. Even if you have typical heating like baseboards of central gas furnace, they can and do fail and for that reason you need backup. Heat pumps are no different, but their efficiency drop off isn't a "failure", it's just a limitation. Being a predictable limitation you can plan for it, and be sure your backup source does not rely on electricity because that always goes out in a storm.

I have a heat pump and I live in Canada where it’s not uncommon to see -40 degree temperatures in winter. The system has a high efficiency gas furnace as the backup (auxiliary) heat source. So far this winter the heat pump has been doing the bulk of the work. Only when the temperature starts to drop and the heat pump can’t keep up does the gas furnace kick in. The system works pretty well.

I just wish the thermostat let me customize the threshold a bit. I don’t like having the heat pump go to maximum load before it lets the furnace come on. Ideally the system would know the current prices of both gas and electricity and run whatever is cheaper, given the indoor and outdoor temperatures.

It'll still work somewhat. Just inefficiently.

Who makes your heat pump? Want to know for my future potential purchase.

We converted about 6.5k sqft of living and work space to heat pumps. Fujitsu. Some commercial products due to sizing. Can generally recommend. Controlling heat pump head units is a little different from typical HVAC. Good systems, very reliable, strong track record in residential and commercial space. New units have good tech.

Thank you.

My 2010 heat pump is a Panasonic model. Panasonic, Mitsubishi, Fuji, Toshiba and others have Nordic-specific models. Several of these reach 1:1 at -30C, and some of them are reasonably efficient even at -25C, which is super impressive when compared to my 2010 model. Obviously they will need regular maintenance, keeping the radiator clean etc, and these are very thin and sensitive so you may have to get a professional to do it.

Edit: Looking at the specs for current Mitsubishi models, they are pretty decent (as in: Getting more out than you put in, and useful effect too) at -25C, reaches 1:1 at -30, or, for some, even colder. At optimal conditions you get 4.4 to 5.5 times as much out as you put in, depending on model and temperature.

Thank you.

Specs from a new heat pump, didn't particularly need to aim for super cold climate so some models can go even lower than this:

- Cooling operating range -22°~122° F (-30°~50° C)

- Heating operating range -22°~86° F (-30°~30° C)

I think the single biggest mistake is differentiating HVAC from heatpumps. The second is not insulating

In the UK most newer offices use aircon to provide both heating and cooling. Its cheaper to put in, requires less maintenance and regulatory oversight.

However the biggest issue is that for any of your heating/cooling systems to work cheaply, you need insulation, and enough of it to do what you need. That means insulating floors, ceilings and walls. Moreover, having a bunch of thermal mass makes stuff a lot more comfortable.

My house is a 1930s semi-detached house. Think harry potter, english suburbia, and you'll get a good idea. It was designed to have an open fire in each room. This means that it has an airbrick in each room, plus a suspended wooden floor, supplied with, you guessed it, a fucktonne of air bricks. This means in its natural state, its windier than an open barn.

This means that with a 30kw boiler (8.4 tons or 100K BTU) working flat out for hours could get the house to about 19c (~66f) at best. Not only that but condensation clung to the walls, meaning a fucktonne of mould.

Combine that with huge south facing windows, meant that in summer the front room hit 37c(98f) with the blinds drawn.

Insulation and new windows with decent coating means that this summer (when outside was 40c) the livingroom's max temp was 27.5c this december we used 1500kwh of gas for heating. (compared to almost triple that in the house across the road.)

Open fireplaces suck a huge amount of air from the room. It was once explained to me that in one particular case (a specific house) the open fireplace would typically suck 150 cubic meters of air every hour, when that was replaced with a wood stove it went down to 15 cubic meters/hour. So, an order of magnitude of difference. Those numbers shouldn't be taken as accurate of course, but at least that house got much warmer simply because they didn't have all that air sucked in from outside all winter.

Those much reviled Insulate Britain folks might have been on to something after all.

Insulation in itself can cause more problems than it solves in some circumstances though, especially when it results in moisture becoming trapped within the fabric of the building.

Cavity wall insulation is one such example where there was a mad splurge of works being done poorly and where inappropriate, the inevitable result being further works required to remove it and make good the damage caused.

Insulate Britain's dream come true would be much more of the same.

> Cavity wall insulation is one such example where there was a mad splurge of works being done poorly and where inappropriate, the inevitable result being further works required to remove it and make good the damage caused

That's called incompetence. Thats what happens when you seal a house that has no mechsnical ventillation.

incompetence us rampant in the construction industry here.

I live in a newbuild, this year communal heating system has burst, and flooded 13th floor with boiling water. Mulpiple residents ended up in the hospital. Where was spectacylar a 50 meter waterfall from the side of the building.

You know why? They used rubber pipes, and they weren't rated to habdle the temperature.

I don't think anyone had an issue with their message - just their method.

If every social movement was always polite and nice with our methods, we'd still be slaving for the lord and dying for the king.

Insulation and air control are absolutely key to efficient heating and cooling, regardless of where you live. We built a stand alone guest house a few years ago. Insulated the entire envelope with closed cell foam to R25 in the walls and R60 in the ceiling. That means it loses or gains very little heat, but also means it exchanges very little air with the outside. It's heated with an 18,000 BTU air source heat pump, although for temps above 0C, just the heat of occupants does the job. To keep it dry and maintain fresh air, it has an outside air circulating system fitted with a heat exchanger. Highly efficient and comfortable down to -20C outdoor temps. Needs supplemental resistance heat when the temps are below that, but that's at most two to three weeks a year here in the upper Midwest. Solar panels make the whole thing carbon neutral in operation, averaged over the year.

Unfortunately, retrofitting existing housing that was not designed to be tight to this level of insulation and air infiltration is enormously expensive, if possible at all. We're getting there, one improvement at a time on our main house, but it takes a lot of check writing.

If your home is sealed tight, then you should consider either an ERV or HRV system as well, depending on the humidity of your environment.

They blow air out of your house and replace it with fresh air from outside, which a fan could do, but they include a heat (and moisture, in the case of ERVs) exchanging plenum so that you don't lose all of the energy that you put into conditioning the air in your house.

They're a little spendy in the $1,000 range, but if your issue is the inside air is too humid and moisture is building up on the walls and windows, it's a good system to use for comfort.

You can also get a whole house humidifier / dehumidifier set for roughly the same price, but that doesn't provide fresh air for your house so I would only suggest that if your air cannot maintain the 30-50% humidity levels that are most comfortable for you with the ERV/HRV system.

They described having an HRV: "it has an outside air circulating system fitted with a heat exchanger."

That's what "an outside air circulating system fitted with a heat exchanger" is.

> The load also depends on unique characteristics of the home like the amount of insulation or the type of windows and doors. A home built in 1850 with no insulation requires more energy than a brand new home. The load is just a technical way to describe and measure all of this.

No kidding. The site is all about switching from carbon, which I am all for, as would anyone that cares even slightly about the planet.

BUT. If you do live in a 1850s house with no insulation, getting a heat pump is a colossal waste of money that will not do the job. No matter how many fancy biased graphs and numbers someone comes up with.

Any responsible heat pump installer will firstly look at your home to determine if a heat pump is remotely feasible. Unfortunately, in the UK, only very recent new builds can comfortably accommodate a heat pump. That or older properties that have had CONSIDERABLE insulation work done to them (and I am talking the expensive kind like internal/external wall work, not just the easy jobs like loft insulation).

Be very careful with heat pump cowboys, if you are getting quotes that don't include a site inspection, run.

As long as the heat pump was properly sized for such an uninsulated home it would still heat it more efficiently than a resistive element heater and just as completely. Of course, if saving money is what you want to do, then yes, insulate before throwing dollars at anything else.

The costs are totally prohibitive, though. We're talking tens of thousands of pounds, whatever direction you decide to take.

You could spend 10s of thousands of pounds in a "properly sized" heat pump system. Or you could spend 10s of thousands of pounds in insulating your home + a more moderate heat pump.

Insulation always pays for itself in the long run, but the period of payoff like peruod of payoff on a mortgage - 10-20 years. We need very generous finance on making home improvements

Yes, it's more efficient than resistive electric heating, but in the UK that is typically not the alternative it's being compared to. The usual existing heating system would be a gas-fired central heating boiler, and the cost of gas vs cost of electricity means that gas is still cheaper, I think.

I'd argue that insulation should be the first thing people consider unless they know their home is already well insulated. It's all very well having energy efficient heating systems but if most of the heat generated leaks straight outside then I'd question whether that's efficient overall. Particularly in smaller dwellings, you can reduce the amount of heating you require each day during winter - often to nil.

In theory I'd agree that you should insulate first. But as others have pointed out, on some older houses, insulation can be difficult to accomplish (especially true in non-wood-framed housing). In such cases it is still a better idea to use LESS energy (because of a COP above 1) to heat that space than it is to use resistive or combustion methods (which have a COP less than 1).

I dont understand how heat output from a heat pump vs heat output from a gas / oil / wood burner / resistive heater are at all different.

Heat is heat, a joule of heat output by the system is a joule of heat ... or am I missing something?

Heat pumps take much longer to heat the system, to get it to the desired temperature. Combine that with a property that is not insulated to very high standard, and you get a heating system that is incapable of keeping you warm.

Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.

Speed / response is a perfectly valid difference. Had not considered it.

Leaky houses are already throwing money at the heating problem, and perhaps with a slower response time you would 'idle' the heating circuit at a passive 25C against 18C room temperature, and throttling up from there. Throwing money at it works!

Maybe they're referring to cases where the heat pump can't supply heat faster than what the building is losing through the uninsulated walls. In such cases, you must first move out of the holey tent before installing a heat pump.

You just need a bigger pump!

I think what the post you replied to meant is that when your home needs a 10kW-20kW heater to actually be able to heat your home, then spending tons of money on a heat pump which (for the largest models) can maybe pump out 7kW of heat (equivalent) under optimal conditions (when it's not that cold outside) then you have paid a lot of money and you're still freezing. So you may as well install something else, even a simple wood stove can provide 10kW or more, sometimes much more.

If you need 20kW and you install a 7kW (equivalent) gas boiler you are in just as much trouble.

If you need 20kW and install a system that can output 20kW under the worst situation (resistive heating), you are probably averaging about 7kW of electric usage when the heating is on to generate 20kW (about 3:1 ratio on average)

Setting aside capital costs that's going to cost you 7kWh per hour of heating. An oil boiler will cost 20kWh per hour of heating.

If your oil costs 40c per litre/$1.50 per gallon and each litre delivers 10kWh, that's about 80c/hour to heat

If your electricity costs 10c per kWh, that's 70c/hour to heat, that's a win

If your electricity fosts 15c per kWh, that's $1/hour to heat, that's a loss

Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump. You can buy the most expensive consumer heat pump you can find, and it won't do at all if you actually need 20kW. So you can as well save the money as you'll have to install a gas heater (or oil or wood heater) anyway.

> Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump.

If even you could, you may not want to. Instead one external heat pump handle heads on the top floor, which is generally bedrooms, and not occupied during the day; a second external unit to handle heads on the main floor, which are generally not occupied overnight.

Each individual smaller unit runs less because the load is more focused in 'zones'.

The other issue is that a heat pump has to keep the output temperature relatively low to stay efficient - so just dropping a heat pump in to replace a wet heating system with a gas boiler will have two problems - the total power is less, and the amount of power the existing radiators can deliver to the room is too low. Effectively heating a house with lower temperature water needs big radiators or wet underfloor heating.

"The Daikin Altherma 3 H HT air source heat pump can provide water with temperatures up to 70°C – the same level as gas boilers – and can work when it’s as cold as -28°C outside."

https://www.theecoexperts.co.uk/heat-pumps/high-temperature-...

Given that there are a lot of existing houses out there, surely drop in replacements should be more prevalent.

That article was generally informative, but they forgot (as far as I could tell after a quick read) to include something very important: How much heat can that Daikin heat pump provide? 3kW? 6kW? 10kW? Can it provide more than a standard air-to-air heat pump which typically can provide less than 7kW under optimal (read: Not that cold outside) conditions? This is important to know before buying one (any type of heat pump)

"from £12,500" I guess it comes in different sizes

To be honest the prices I see out there are still generally 'luxury' anyway. If i am spending £20k on a boiler, then an extra £2k to have a secondary gas system that never/very rarely gets used wouldn't bother me at all.

It can make leaving water temps (LWT) of 70°C. It can work when it's as cold as -28°C outside.

What it can't do is both at the same time: make 70°C LWT when it's -28°C outside. It's designed for 65°C LWT (some models 60°C) and can only reach 70°C at a performance penalty (year-round) and can only maintain 70°C LWT down to -15°C and starts to lose max LWT, heating capacity, and even more efficiency below that. (Losing efficiency a few days out of the year is a minor concern. Not being able to meet the heat loss and heat transfer for the building for a few days is a much more serious issue for health and comfort.)

Heat pumps can't be more efficient than the theoretical Carnot heat engine running in reverse, whose efficiency is T_outside / delta_T. In this case it's (273-28)K/98K = 2.5.

I guess being 2x as efficient (cheap) as electric resistive heating isn't super-terrible, but it's not great either.

Compare this to a favorable groundwater heat pump configuration with good radiators and insulation where the 'outside' (groundwater) is maybe 10°C and the target temp 30°C (close to room temp): (273+10)K/20K = ~14.

To understand the difference in a short and simplyfied way:

1. Your examples are heating up the inside air by using energy (burning fuel). Doing so will always be less than 100% efficient, some heating technologies are as little as 10-20% efficient (energy per kWh)

2. Heatpumps are instead using energy to do heat transfer. Moving heat from the outside to the inside.

The latter is way more efficient, with easily 300-400% efficiency. But obviously the colder it gets outside, the less heat is in the air to extract and the efficiency goes down.

It's not different but the amount of heat that each system can be generated is different. And when it's cold (i.e. when you need the extra heat to be compensate for your draft home) your heat pump is going to struggle most.

> I dont understand how heat output from a heat pump vs heat output from a gas / oil / wood burner / resistive heater are at all different.

A gas/oil/wood burner are not 100% efficient in creating heat, and release carbon into the atmosphere.

A resistive heat is at most 100% efficient: all the electrons go to making the coil glow, like old school light bulbs. So 1 kW of electricity is 1 kW of heat (which has some BTU equivalent for old fashioned folks).

A heat pump does not create heat, but moves it from one place to another with refrigerant and pumps. So 1 kW of electrical usage can move 3 kW of heat at times:

* https://en.wikipedia.org/wiki/Coefficient_of_performance

* https://energyeducation.ca/encyclopedia/Coefficient_of_perfo...

So if you input 1 kW of energy, do you want 0.9 kW of heat out (carbon), 1 kW of heat out (resistive), or >2 kW of heat out?

The $/capacity may be quite different. The capacity of burner systems is generally cheap, so you oversize them and if you need more heat, you just burn more fuel. The capacity of a heat pump is relatively expensive, so you size it up to something reasonable, and in an unusually cold day you may hit the limits of how much joules you can get out of it.

Also, the $/fuel is different - if one system gets three times more joules from the same fuel, it doesn't mean it's more efficient as the other system may be using four times cheaper fuel; so a 300%-efficient heat pump is more efficient than a resistive heater but may be less efficient than a furnace burning cheap fuel.

The key issue is despite claims that cold doesn’t affect heat pumps it absolutely does. We have an old house. When very cold the heat pump struggles to put out enough heat. It works well enough, but something to be aware off - go bigger in system than you think you need maybe

"go bigger" will result in short cycling during the hot summer resulting in high humidity and mold problems in the summer.

Untrue. All modern heat pump systems use DC motors ("inverter technology") and will run continuously at variable speed until target temperatures are exceeded by a (programmable) margin. They do not turn on and off and on and off.

Nobody says that it has no effect. Only that efficiency decreases. And that even at diminished efficiency it's still better than a boiler.

Could you elaborate a bit? My parents live in a not-very-well insulated wooden house from around 1900, and use a heat pump as their primary means of heating the house. This is Scandinavia, so it might be that this house (despite not even coming close to modern insulation standards) still has better insulation than most British houses, but it would surprise me (older British houses are generally built in brick, which should provide a better base level of insulation than a wooden house, and I'd think Britain isn't warm enough that nobody would build a house without any insulation whatsoever).

Maybe I don't understand what you mean by the word "feasible" – they don't have a goal of getting their living room above 23 C at most in winter, and I guess heat pumps are insufficient in such a house if you desire ambient temperatures above that. However, while other means of heating could plausibly bring the temperatures higher, that would end up being very expensive also because of the poor insulation – it's just harder in general to heat a drafty house and keep the temperature up, and I don't see how heat pumps are a uniquely bad choice for homes like that.

Edit: This is coastal Norway, so the climate in winter is quite similar to somewhere like Edinburgh, with temperatures usually above 0 C in January. The heat pumps would probably be insufficient somewhere the temperatures regularly reach -10 or -20 C, but that's a very infrequent event both here and in the UK.

British houses generally have terrible levels of insulation and if built before roughly 1930 are likely solid walled, so have no wall cavity to insulate. There is also the issue that a lot of people live in terraces and semis and there may simply be no suitable place to install a heat pump. When I looked into it for my house a couple of years ago the fitters basically said they couldn't do it because of lack of space.

I live in an apartment in a UK 1850s house, it just has solid exterior walls.

I think there are now heat pumps that are a similar size to a gas combi boiler and are designed to be inside a building, not a big box outside.

Interesting - https://groundsun.co.uk/small-home-and-apartment-heat-pumps/

There isn't that much to elaborate on. Commercial heat pumps just aren't good for the average UK house. They would be "alright" if the costs weren't prohibitive.

I don't know the specifics of your parents. A "wooden house" with a heat pump acting as the primary heating system in a country like Norway sounds fairly bad on the surface. But I don't know the insulation specifics, nor do I know what other heating element might come at play when the heating pump fails to keep up with the heat loss. Also, what heating pump are we talking about?

Heat pumps work extremely well in the Nordic countries and are therefore very popular. That's because due to the cold winters houses are already well insulated, though very old houses less so. Which means the houses are in general reasonably energy efficient to start with, so a heat pump providing 3.5-6kW of heat is generally sufficient. That would be to the main area of the house, so yes the heat pump is the primary heating system (for those who use them) in the sense that it's the heater used for the main parts of the house - think living room, kitchen area. There may well be normal electric heaters in other rooms, if deemed necessary, but other rooms (food storage, bedrooms etc) don't usually need much, if any, heating).

Of course in the Nordic countries you also have areas very far from the ocean, and there it can get very cold. Down to -50C in some cases, and regularly -30C or colder. I imagine heat pumps aren't used much there. But elsewhere (i.e. most places) they are great. In those places you see them absolutely everywhere now.

+1 to this. I had a hpwh installed for my radiant system and after paying >7k to get it up and running, I learned that this model is entirely unsuited to that setup and Rheem refuses to accept a return.

If anyone wants a barely used 120 volt hpwh in the bay area, get in touch.

Down to -20C, and even -25C:

* https://www.mitsubishielectric.ca/en/hvac/professionals/fs-s...

More advanced unit (primarily for hydronic heating) that goes down to -20F / -29C:

* https://www.spacepak.com/solstice-inverter-extreme

The lie / part skipped is while they “work” to those temps, they don’t work well.

If you get to -20C a couple of times a year but normally it's -5, it doesn't matter that it's inefficient for 2 or 3 days a year, as it's very efficient for 360 days a year

It doesn't matter for you personally, but it kind of matters globally. If everyone hits that same inefficiency at the same time then there needs to be a lot of extra capacity in the electric grid that can be spun up during a small part of the year.

There's already plenty of spare capacity in winter time that is necessary to support peak demand in summer time. Loads like electric heat pumps are also perfect candidates for automated management to smooth out load spikes, so there would be no "at the same time" to worry about.

https://learn.pjm.com/three-priorities/keeping-the-lights-on...

> There's already plenty of spare capacity in winter time that is necessary to support peak demand in summer time

That's not the case at all in very cold climates. Here in Alberta we get grid alerts when it gets extremely cold and that's with the vast majority of houses being heated by forced-air natural gas.

https://globalnews.ca/news/9364926/cold-weather-grid-alert-a...

Those are general demand curves, and are not necessarily representative of the coolest days of the season. What we care about is the gap between supply and demand.

From experience buying large industrial quantities of natural gas, the larger market can see bad effects at low temperatures. Even in the upper Midwest you can get force majeure events, particularly when temperatures drop below 0 F for a couple days.

The winter months bring planned shutdowns for power plants to perform maintenance, trying to prevent downtime during the summer heat. The non-linear nature is a concern, though in cases almost up to the 1:1 point, it's more energy efficient to burn natural gas to create electricity and use a heat pump compared to burning natural gas in the home.

Extra capacity and/or reduction in demand.

The issue I’ve seen is need for heat goes up a LOT in older houses when it gets that cold, and the heat pump without resistive heat performs a lot worse (like 2x+ worse).

So it’s a noticeable combination

Why would you install heat pump without properly insulating home first?

Because the labor to properly insulate a home can be quite extensive, while the labor to install a heating unit is typically less than half a day.

Take a structural brick house built with no cavity insulation, plaster walls, and a finished interior and try to get any amount of additional insulation into the walls. You end up having to destroy and repair the finished plaster walls, which is obviously prohibitive from a labor cost standpoint. Those projects can be (and usually are) done when remodeling/redecorating is already planned (so you don't double-pay for finish work), but are economically unrealistic to do just to save on HVAC.

IDK about US wooden houses, but here isolation for old building is usually done on the outside on the top of previous finish with styrofoam or mineral wool: https://d-art.ppstatic.pl/kadry/k/r/1/70/9e/60644af2aec93_o_...

>economically unrealistic to do just to save on HVAC

That depends on how much the HVAC costs... I saw some videos from last USA freeze where people had ice (!) inside of their homes - I doubt heating that is in any way economical.

There are plenty of insulation firms that specialize in insulating old homes without ruining the finishes. Typically you cut a small plug, either from the outside or inside depending on the construction method and mechanically force (typically blow) cellulose fibres into the wall cavity. You need one plug per stud bay, but repairing those is a pretty simple job compared with tearing down all the finishes.

Air sealing is tougher, but techniques like aerobarrier where an aerosolized polymer is sprayed throughout the home while it's under positive pressure has made air sealing fairly simple. Stuff like that can plug up to multiple inch gaps

The "cut a small plug into each stud bay" works very poorly when the wall material is 9" thick structural brick and there are not studs, but rather lath and plaster (and often wallpaper) on furring strips.

If you seal your house you have to worry about moisture removal otherwise you're going to be getting damp issues.

Lath and plaster can be extremely expensive to repair. Sealing old houses has problems in terms of moisture- many old houses depend on evaporation in various ways- list goes on

But it does mean you need a reliable backup heating system, because the very inefficient at -20 is also when you need the most heat.

No, that's about the capacity of the heating system at -20, not efficiency. It does mean that the system will be oversized for the days it doesn't get that cold.

There is no lie / part skipped, what that number is meant to tell you is that it reaches its 1:1 point there, so it "works", with diminishing returns, down to that point. Which is where it's as "efficient" (to put it that way) as a resistive heater.

Obviously you need to take that into account - is the amount of heat you get out of it sufficient for nominal winter temperatures, at its coldest, for where you live? (geographic location and building conditions). As for myself, I have a backup in my wood stove, but I only need it under special circumstances (like last week when it was particularly cold and no electricity for parts of two whole days because I had electricians doing major rewiring in my home).

You can get a ground source pump which doesn't care much about the air temperature as its "heatsink" is above freezing even in extremely cold days.

The biggest issue with mass-scale installation of heat pumps is non-linear load on grid in cold weather. Failing efficiency and ultimately automatic switch to resistive heating causes electricity consumption spike, together with other accidents caused by the weather (be it reduced generation or grid damage) it can cause brownouts or full-blown blackouts. In other words, people can lose heating when they need it most.

Any programs which promote heat pump installations above a certain scale must either include huge investments into grid robustness or mandate that all heat pump installation must include fuel-based backup heating sufficient for a week or two.

This is why the technology is best combined with geothermal concepts. You only have to go a few feet deep to get warmth and that solves basically every problem a heat pump has.

Only a few feet deep? Maybe in select areas, but you generally have to go a lot deeper than that. It's been my understanding that the steep cost of geothermal involves the drilling. As much as $80K just to install a decent system, from what I've heard.

Some geothermal systems use deep wells, others use coils of pipe buried a few feet down, below the frost line. If you're lucky enough to have a deep pond or lake nearby, you can put the coils of pipe in that.

In my understanding, it takes more to maintain such setups. Talking to the HVAC guys that do this for a living rather than just the scientists reveal more about the practical realities of these systems.

if you have land a horizontal trench at 7 ft will work just fine. I was going to do this on a new build but building code basically required a heat pump to start with. I was going to put in a cheap furnace for the first year or two and install a ground source heat pump myself, but with the cost of my regular heat pump it will never make sense to change over.

A lot of it depends on how you design the system.

Using the ground as a heat source requires a relatively large installation as you need to make it big enough to draw heat from a large area, even as you use it year after year.

However, you can also use the ground as heat storage, and pump back heat during the summer. This greatly reduces the size, as you are not at risk of "exhausting" it.

Geothermal is just too expensive. Just have a propane or diesel heater around for (hopefully rare) emergencies.

> Any programs which promote heat pump installations above a certain scale must either include huge investments into grid robustness or mandate that all heat pump installation must include fuel-based backup heating sufficient for a week or two.

That's a little extreme. You also need to consider your failure modes. I live in texas where a bunch of people died due to an extreme freeze and a very poorly regulated grid. When that happened, it wasn't just electric that was lost, but a big problem was natural gas wells and pipes freezing up too.

The cost to install and maintain both systems would be an automatic deal breaker for many people. I don't think you need total redundancy, but having some is good. For example, I went and bought a "buddy heater" after that freeze. It runs off of a 5lbs canister of propane and has an automatic Carbon Monoxide cutoff. It gets toasty. It won't last forever, but it's a good emergency backup.

One thing I think everyone needs: An emergency radio with crank power. When the grid goes down, so does internet and cell towers. The only way we got news was via radio.

Let's do some basic math:

The US average cost of electricity is 16 cents / kwh [1]

The US average cost of Natural Gas is $10.84 / thousand cubic feet [2]

A thousand cubic feet of natural gas contains around 300 kwh of energy [3]

So natural gas is around 4 cents per kwh. Gas furnaces are extremely efficient, buts lets round up to 5 cents/kwh to be conservative.

So a heat pump needs to maintain a COP of 3 just to be in the same ballpark as natgas in terms of cost, and closer to a COP of 4 to be cheaper. Heat pumps "work" down to -20F or so, but the efficiency severely degrades. Heat pumps as a sole heat source are not cost competitive in cold climates.

I have a heat pump in New England, and it is wonderful for 3 seasons of the year. I think all new construction should have one. But the cost to heat during winter is ridiculous. I am very glad I had an auxiliary natgas heater put in.

[1] https://www.eia.gov/electricity/monthly/epm_table_grapher.ph...

[2] https://www.eia.gov/energyexplained/natural-gas/prices.php

[3] https://www.eia.gov/energyexplained/units-and-calculators/

The full cost of fracked methane gas is not actually included in the price.

I'm not just talking about the environmental cost: gas consumption and production is subsidized by tax dollars, and the health costs are poorly quantified but my understanding is a growing body of evidence links gas usage in the home to childhood asthma and other chronic health issues.

The asthma issue is with gas stoves. It is irrelevant with respect to a proper gas furnace. None of the exhaust from a modern furnace enters the home air supply.

By the way, if you are going to consider environmental costs for gas you should also consider those costs for electric.

One note on energy in nat gas: that assumes 100% efficient gas furnace. Cheaper furnaces are ~80% efficiency. Really good furnaces are ~95% efficiency.

Adding natural gas infrastructure to a building that does not currently have any is extremely expensive, even if the natgas furnaces aren't particularly expensive themselves. I agree it's cheaper if you have it now, but that assumes you already have a gas furnace.

I think the fear for most people is that natural gas can easily become substantially more expensive. European natural gas pricing is currently ~$20/mcf, and spiked to ~$80/mcf for some time. Natural gas pricing limits you to a single source for power... whereas power inherently has many sources it can come from. If natural gas becomes more expensive... you're stuck paying more with the furnace. With heat pumps, there's options available to alleviate pricing either for producers or for consumers (namely, solar for consumers).

Also, importantly on the COP point: you need to talk about the area under the curve in terms of cost. Although it may be more expensive per unit of heat when COP drops below ~3, you have to think about it in terms of overall cost. A furnace will be the same efficiency if it's -50F or if it's 50F outside (for the most part...). So for the periods when it's mild, but heating is still required, the heat pump is an obvious winner. I suspect that the math works out in favor of heat pumps, even with reduced efficiency during winter, for many climates. The only thing is that you'll get a much more peaky power bill. Obviously there's exceptions, but there's vast swaths of the world where a heat pump is going to make a ton of sense.

It sounds like you agree with me...

> that assumes 100% efficient gas furnace. Cheaper furnaces are ~80% efficiency. Really good furnaces are ~95% efficiency.

>> natural gas is around 4 cents per kwh. Gas furnaces are extremely efficient, buts lets round up to 5 cents/kwh to be conservative.

> So for the periods when it's mild, but heating is still required, the heat pump is an obvious winner

>> it is wonderful for 3 seasons of the year. I think all new construction should have one. But the cost to heat during winter is ridiculous.

>> Heat pumps as a _sole_ heat source are not cost competitive in cold climates.

Sure, totally agree with you on that for truly cold climates. My only note would be that using natural gas as a backup/emergency source for cold climates only makes sense if you have existing gas infrastructure there... and it still makes sense to upgrade to a heat pump assuming that you don't live in a climate where it's just frozen constantly (e.g., parts of Canada, Alaska, etc)

Even just routing a new gas pipe to your HVAC closet can easily be $5-10k, which would erode all potential savings during the truly cold parts of the year... not to mention the additional cost of a furnace + emergency heat wiring etc.

In Eastern MA electric is 26 kwh, and $15.00 per thousand cubic feet as per January 1st.

Most natural gas furnaces are between 80-90% efficient, but to get above 80% you need to have a high power electric fan. Which would put them roughly at 6 cents per kwh or (0.0625 for 80%).

At COP of 3, that would mean 8.66cents per kwh, and a COP of 4 would be 6.5. Which would roughly be breaking even compared to 80% efficient furnace.

My electricity is 8.7 cents per kWh so that helps.

Some cautions

- noticeably lower heat output at cold temps.

- install is important, many installs done get adequate ventilation- so cold air collects near unit.

- high ceilings can be an issue, evaluate fans to bring heat down

- gas is amazing for heating in radiant heat. We really like our radiant heat experience- global warmth and good volume

- I’m not sure if tech term, but heat volume can be an issue. We are in a 100+ year old house. The heat pump in very cold weather seems able to generate heat, but no where near quantity that gas system did if you just cranked it

- we are getting hit with tier three electric rates - switched dryer to electric etc - costs get tough!

Also this whole conversation is specifically about air source pumps. Geothermal are immune to air temperature fluctuations with the tradeoff being higher installation cost.

If you use geo thermal in combo with heat pump, efficiency is even higher and you are not afraid even -40 -50c , you still save money. NY state will ban oil burners from 2025 for the new construction. Geo thermal is super easy just put few pipes under the ground and save money.

Define “super easy”. Last time I checked geothermal installation was quite expensive due to having to move a lot of earth for those “few pipes”

There are two variants. One move a lot of earth and one drills deep holes. Both are pretty expensive though.

One variation of putting a coolant loop into the ground is to just cut a deep narrow trench and loop the coil in it like a slinky pushed "sideways".[1][2]

[1] https://dandelionenergy.com/geothermal-ground-loop-frequentl...

[2] https://www.energy.gov/energysaver/geothermal-heat-pumps

> Contrary to popular belief, modern cold-climate heat pumps can heat a home efficiently even when the temperature drops below -10 degrees. At this temperature the best cold climate heat pumps are still more energy efficient than furnaces and boilers

This is maybe true if your house is insulated to Scandinavian standards. Our heat pumps here in Maryland get iffy around 20 degrees in our circa 2005 house. We have a nice oil burner heating a hydronic system that does a great job at that point.

> We have a nice oil burner heating a hydronic system that does a great job at that point.

A primarily for hydronic heating unit that goes down to -20F / -29C:

* https://www.spacepak.com/solstice-inverter-extreme

Having a heat pump transfer the energy to heating water that is then circulated in radiators is becoming quite common in the Nordics, and often used as a replacement for an oil burner. It's more efficient than a regular heat pump that just uses hot air to warm the home.

Of course dealing with crappy insulation can often be more bang for buck.

If you believe lack of insulation is the problem, the heat pump is just underpowered. A more suitable model or, even better, adequate insulation, would likely be a triple win financially, environmentally, and for your and your neighbors' health.

In my part of Canada it is common to have mini-split (non-ducted) heat pumps, mainly for cooling. The salespeople like to say that you will save a lot on heating with a COP of 3. However the placement of the inside unit is always close to the ceiling, usually in the highest part of the house. This is perfect for cooling during summer. However during winter, it causes the upper part of the house to be hot and the floors to be cold. The basement resistive heaters have to compensate to maintain the target temperature. This means that these single head mini-split heat pumps cannot replace 100% of your heating and cannot provide the same level of comfort than resistive baseboards.

What you say is true, though another approach that could be more efficient is to simply run the heat pumps with a higher setpoint rather than supplementing them with [as much] resistive heat (especially in the majority of season that isn't the coldest design day).

It might "feel wrong" to set the heat pumps to 25°C, but that could easily be cheaper and more efficient than setting them to 20-21°C and supplementing to the same level of comfort with CoP of 1 resistive heating all season long.

I have the same setup as GP and setting a higher temp doesn't help at all. My thermopump is in the main hallway on the second floor and blows towards the master and second bedroom, above the stairs. In summer it's great because it sends cold air everywhere and lets it sink to first floor. In winter, it just creates an insufferable hot bubble on the second floor. I already prefer to sleep in the cold and just use baseboard heaters on the main floor and bathroom. I don't even heat my bedroom.

Sounds like a ceiling fan or some sort of air circulator is in order. If you put a ceiling fan on blow to push the hot air down it will blend with the air in the rest of your house and improve the overall comfort of your space.

If that won't work, for instance your home is very boxy and separated, it might be worth looking into AC duct boosters on the far away areas to suck more air out of the ducts from farther away.

If I misunderstood and you have a ductless system, they make electric fans that go in between paired walls and look like a ducted register, but that are very useful for blending air between two rooms. A few of those alongside a through floor to ceiling below fan duct might be available that could help even out temps in your house even more.

Do heat pumps not just work in an "on/off" fashion that shut off when the thermostat say "ok, that's enough"? I know that modern forced air natural gas furnaces are a little smarter and will have stages to balance for noise, but they are really just "on" or "off", pushing much hotter than ambient air around until the rooms settle to the desired temperature.

Most heat pumps now are variable speed/output. I suspect all low-outside temp capable heat pumps are variable speed/inverter drive.

Is the speed/output a high/medium/low type deal or a specific temperature?

The outdoor unit can vary the frequency of the compressor drive to track a desired refrigerant temperature in the face of varying load from the indoor unit. As the indoor air comes closer to the desired temperature, it will cool off the returning refrigerant less than when there is a large delta-T. The outdoor unit can adjust the compressor speed to closely match the heat transfer and run continuously at a lower speed rather than cycling on/off. There is a minimum speed below which the compressor can't run [and so would have to cycle], but in general the outside unit is smoothly variable.

The indoor unit fan speeds are only loosely connected to this. (The higher the indoor fan speed, the greater the heat transfer and load on the compressor, all else being equal.)

This is one of the critical problems for heat pumps being a silver bullet for climates that are both hot and cold. You buy them for AC but they dont work for heating due to the physical location or alternatively you need another heat pump that is cost ineffective. That and it gets quite expensive to heat in cold weather.

My part of New Mexico (6000'/2000m) may not get as cold as your part of Canada, but I simply have not found what you claim to be true.

My house has several "lifted ceilings" (15'/5m) and it is true that the heat from my minisplit units wants to accumulate up there. In some rooms we have ceiling fans that help move the air down (or up). In other rooms, there are no fans, and the upper part of the room space is indeed way, way hotter than the lower part, which is ridiculously inefficient.

HOWEVER ... this has never impacted the ability of the minisplit units to provide more than the same level of comfort as floor-mounted heating devices.

Heat pumps don't have to be air-air pumps. Most commonly these days I hear people installing air-water heat pumps to replace gas furnaces that heat water for radiators or under-floor heating. For new houses around here, ground-water heat pumps are actually most common as they are very efficient even if it's cold outside, but they require diffing up a large area to install the under-ground piping.

My wife’s uncle has large pond outside his house and wedding venue. He has two units. One closed and one that directly draws the water. The closed unit has half a mile of coils sunk in the pond. He says the open unit is more maintenance.

His heating and cooling bills are not far off from my house. Considering he has 3 buildings similar sized to my house it’s a pretty drastic reduction.

Yeah, there are of course also water-air, water-water pumps (although I've never heard of the open-circuit ones, but yeah, why not). But you have to have access to a large enough body of water that doesn't freeze and has enough capacity.

The main issue for me with air-X heat pumps is that over time it can start to make a lot of noise if not well maintained.

But the closed-circuit under-ground (or under-water) ones essentially don't need maintenance and are incredibly efficient, as the source never goes very cold.

My tips would be: (sorry if they are a bit obvious)

1. Make sure to point the vents down so the hot air blows into the lower area. (And naturally, in the summer when you use them for cooling they should point up)

2. Set a higher temperature. The thermometer tends to be part of the unit itself so it tends to measure the hottest spot in the room (both when heating and when cooling), so you think you are wasting money blasting the heat to 25C when actually it is just that the unit isn't running since it only keeps itself hot. Some units come with a function that pretends to use a thermometer built into the remote, but I don't think I've ever seen it do anything other than burn through the batteries.

3. Since you are talking about mini-split heat pumps (plural) I assume you have one per room so a good tip here would be to close the door to that room.

For my own needs they are more than enough, but then again it doesn't get quite as cold in Israel as it does in Canada :)

To get rebates in NS need to put a head per level. Also the systems can typically work a temperature sensor that's not in the unit. It can be in the remote or in a wired thermostat. This avoids the unit shutting off because the ceiling is hot.

Mini splits don't have to be installed high up on a wall, indoor handlers come in a variety of form factors, you can get thin "console" units that are floor mounted against the wall.

Put circulator fan to mitigate

Our house (in Northern New England) has heat pumps (which we added in the last two years), a wood stove, and hydronic baseboards powered by an oil-fired boiler (which we now use as backup). The heat pumps so far are able to heat just fine, and are great for maintaining temperature while we aren’t at home. However, we much prefer the comfort provided by radiant heat: wood stove and baseboards. Once the boiler needs replacing, we will likely switch to a wood pellet boiler so that we can use the radiant heat more when it starts to get colder/before the wood stove had heated up in the morning/when we get home in the evenings.

You can get air-to-water heat pumps (e.g. Chiltrix), and some manufacturers have refrigerant-to-water accessories for conventional systems. So you could have a heat pump heat your floors.

Thanks for the pointer. I’ll look into Chiltrix. However, based on my state’s tracking of heating fuel prices, wood pellet is by far the cheapest [1] and is a local/regional resource.

[1] https://www.energy.nh.gov/energy-information/nh-fuel-prices

We're in Vermont in a house built in 1926. We blew insulation into the walls, insulated the attic well, and replaced the ground floor windows (some day we'll do the rest of the windows; in the meantime we use plastic film in the winter). We heat with pellets primarily, but when the pellet stove starts to struggle we turn on the heat pump we installed a few years ago. It warms up the house in no time.

I actually prefer the heat pump over radiant heat. My heat pump is placed low on the wall, about a meter or a bit less above the floor, in one side of the living room. Due to the air it's pumping out I get an even nice temperature everywhere, while if I use the wood stove with the heat pump switched off it gets very hot near the stove while it's cold in the other section (around the corner) of the living room, not to mention the kitchen. In practice I end up pouring in wood fuel and let the thing burn to maybe 10kW just to get the warm air seeping into the kitchen, eventually, and then it's too hot elsewhere. I realize I could set up fans etc, but really - it's so much nicer to use the heat pump and get a uniform heat distribution.

We tend to leave the mini-splits on but turned down to their minimum temperature when the wood stove is on. The fans of the mini-split stay on and circulate the heat around nicely.

I'm a air-to-air heat pump owner and I love it and think they will be a key part of climate mitigation.

However, from a climate change policy perspective, it is important to _emphasise_ that heat pumps are less efficient at lower temperatures (lower COP) and not try and pass this off as a myth. (I recognise this article is presenting the 'myth' as operating at a COP of < 1, but many people will misinterpret that)

To put this in perspective in the UK, in mild weather demand is something like:

- about 40GW total electricity demand

- about 100GW of gas

In mild weather, my heat pump gets a COP between about 3 and 4. Which means that, if we want to replace gas usage with heat pumps, we need a further 25-33GW of electricity to power the heat pumps.

This is eminently achievable. See here https://twitter.com/heatpolicyrich/status/161238524325157273... and the latest edition of the economist quotes there being 260GW of wind projects in the pipeline for the North Sea (amongst 9 countries): https://www.economist.com/leaders/2023/01/05/why-the-gusty-n...

In extreme cold snaps, total gas demand doubles to about 200GW, and electricity goes up to maybe 60GW.

The problem is that now the heat pumps are getting a COP of maybe 2, if you're lucky.

So now in the UK we need 100GW of electricity to replace gas, which is a big ask even when the wind's blowing. At the moment, wind output peaks at about 21GW, though records are being broken all the time.

None of this is to say we shouldn't switch to heat pumps where possible. Mine was cheap to install (£1,895+vat) and has halved my gas usage. Must be one of the most cost effective way of mitigating the current gas crisis (after reducing usage!). I think it's just worth understanding some of the important numbers.

Also worth adding that in the UK new homes will not allowed to be built with boilers by 2025 and they will need to be slowly phased out in next decades so definitely invest in home insulation and a heat pump if your boiler is on the way out!

Yes - good point.

That touches on another myth I've heard frequently - that heat pumps are only suitable on well insulated homes. I think this may be true in relation to some air-to-water systems (?), but it ignores the possibility of just installing a cheap air-to-air system on top of existing heating (either gas or air-to-water).

Air to air systems are really well suited to homes with a combined kitchen/living room which is the main room in use most of the day. We only heat the kitchen/living room during the day (our main living space), and the heat pump is more than adequate for this. It typically uses around 10kwh a day for quite a big, not very well insulated room.

The trouble is that the electricity demand is always topped-up by gas-fired generators. It's always there at the margin. Things like nuclear and renewables usually run at 100% of their ability, their generation is not affected by demand.

Therefore any increase in electrical demand is made up by turning up the gas-fired generators an equal amount.

So if a heat pump has a COP of 3, and the additional electricity consumed is generated from gas with, say, 33% efficiency (from the gas burner to the house electrical meter), there would be zero net change in overall gas consumption by converting from a gas boiler.

This is especially the case in winter, which is when most heating demand is, and the gas generators are definitely going to be running and making up that marginal generation.

My understanding from the Technology Connections youtube channel is a heatpump has a typical COP of about 3.5 and a gas power plant about 45% from plant to home, making it more efficient to use the gas to generate electricity to run the heat pump than to burn the gas directly for heat.

Plus you can also use the waste heat from the power plant to heat some more homes.

He made several excellent videos explaining residential heat pumps:

[2021-02-28] https://www.youtube.com/watch?v=7J52mDjZzto "Heat Pumps: the Future of Home Heating" (35m14s)

[2021-04-01] https://www.youtube.com/watch?v=7zrx-b2sLUs "Ground Source / Geothermal Heat Pumps and Other Info" (28m03s)

[2022-03-26] https://www.youtube.com/watch?v=MFEHFsO-XSI "Why Heat Pumps are Immensely Important Right Now" (21m02s)

[2022-04-13] https://www.youtube.com/watch?v=43XKfuptnik "Heat Pumps are Not Hard: Here's what it will take to start pumping" (46m32s)

The idea to moving everything to heat pumps right now isn't so that you immediately reduce carbon emissions, but that everything works off of electricity and the grid so that as offshore wind, onshore wind, solar and Hinkley Point C come online it can start to replace fossil fuel energy. Same with EVs.

If you stick with gas boilers there is really no exit strategy for getting off fossil fuels.

> - about 40GW total electricity demand

> - about 100GW of gas

That gas demand should be 70% less, UK has the worst insulation in Europe.

https://theenergyst.com/europes-leakiest-homes-new-study-fin...

There are countries where bombs fell, then communism fell, then bombs fell again, then their currency collapsed, and the houses are still better insulated.

Need to check my math but a heat pump that can do a COP of at least 2 powered by a 60% efficiency natural gas power plant should be more efficient than a 90% efficient natural gas furnace. That's not even counting a renewable/nuclear mix on the grid or say solar on your house.

Air source heat pumps are technically solar, they take heat from the outside air which was warmed by the sun.

Even better would be geothermal ground source heat pumps but the install costs and complexity are much more.

Electrification has so many advantages since your decoupling and abstracting power source from use, now your car or your house heating is not tied to a specific fuel.

In my area natural gas is 3x cheaper than electricity per kwh, so you might be right that the electric solution you outlined uses less overall energy but the end user will be punished with a higher overall utility bill.

Also, in cold climates where gas heat is typical the overall energy needed to heat the house is very large compared to typical winter electric use, which will likely anger homeowners after heat pump installation.

In my area it's about 2.6x so a heat pump only needs to have a COP of about 2.4 to equal the cost of natural gas per unit of heat delivered when compared to a 90% efficient gas furnace. These modern air source low temp heat pump can maintain a 2.4 COP down to about 17F.

Note my area is pretty warm (FL) so even though I have natural gas to the house for cooking and hot water I do not use for that as my air heat pump works very efficiently in the cool temps here. I have resistive heat as a backup and it never turns on.

Geothermal heat pumps can maintain 3-4 COP year round in any temp then your easily surpassing natural gas even at 3x the cost.

I have a heat pump and a wood stove in my house. The heat pump doesn’t do as good of a job, but it keeps one from freezing and it really shines in the summer at cooling the house.

Heat wise the wood stove is much nicer. I can’t quantify why, but the quality of heating feels completely different and I’d much rather use it.

Additionally as someone who has used a heat pump in -25C I dispute the claims they work well in the cold with personal experience. If I hadn’t had backup heat I’d have been way, way too cold as it didn’t heat acceptably at that temperature.

Did wood stoves become a trend recently?

It happens every time oil/gas spikes. Heating oil was just pushing $6/gal, so yeah.

And the federal tax credit just got severely neutered. At least that's what caused me to install a new one at the end of last year as opposed to later this year.

Wood stoves and heat pumps would seem to pair well. Heat pump capacity is expensive, and drops precisely when you need it most. Rather than falling back to resistive heat for the small amount of coldest days and watching your electric meter spin while you shiver, you can focus on the wood stove and have plenty of heat. On most days, you can keep a fire going if you're home and you want to, or you can just let the heat pump do its thing. Also unless you have a huge backup generator (and a correspondingly large fuel source), a heat pump isn't going to work in power outages while a wood stove will.

Not where I live, in rural Nova Scotia almost everyone has one if not for primary heat, than for when the power inevitably goes out.

People here are not well off and wood is hands down the cheapest heating option. In other places? Maybe it’s a fad/trend.

The EPA was going to ban them, so everyone who still used one got very vocal, along with about a third of the state of Maine.

>> I can’t quantify why, but the quality of heating feels completely different and I’d much rather use it.

It is because your wood stove is radiant heat. It is pumping out IR radiation which is heating all of your surfaces, as opposed to heating air that is then moved around your house. It is the difference between standing in a warm breeze and standing under a heat lamp.

This is exactly it. You get a similar experience with the old radiators powered by a boiler. Both have the added advantage of not having as many issues with humidity as say forced air heating, which dries the air out as it heats it.

I grew up in a house heated primarily by a wood stove and setting aside all the environmental issues, it’s incredibly comfortable. I lived in an apartment for a few years that was heated by a boiler, and it was almost as comfortable (a bit louder though, but there’s no smoke to deal with). Midwest Winters were quite comfortable there. Unfortunately that apartment had no AC, so the summers were pretty brutal.

It depends on the setup. Some radiators are meant to sit in the corner, heating air, which then circulates around the room like in baseboard heating. Wood stoves are generally in the middle of the room and "visible" to everything, allowing them to radiate more. Radiator colour can make a big difference too. A black radiator will radiate more than a white one. Wood stoves are generally dull grey/black. Radiators are often white/shiny.

Color has extremely little effect on radiation performance: https://www.bestheating.com/info/does-the-colour-of-your-rad...

Air-to-water heat pumps provide radiant heat too.

There are also IR panels that provide radiant heat directly (although with COP=1).

> Heat wise the wood stove is much nicer. I can’t quantify why, but the quality of heating feels completely different and I’d much rather use it.

Radiant heat, it reminds us the bonfires, which kept bad things away. I also like my fireplace much more than more convenient to handle wood pellet furnace in my basement, but warm floors are nice too.

Agreed this is the best combination. Wood stoves are also great for when the power is out. If only my building would let me put a fire in my apartment. :)

I recently replaced a (very) old gas boiler with a new gas boiler after trying and failing to make an air-to-water heat pump make economic sense. (It 100% would have worked technically/thermodynamically.)

It was going to be a bit over $20K more, which at only 4% opportunity cost of that money (low, IMO), means that an $800 savings per year would literally never pay back, let alone within a 20-year projected service life. I’ll re-evaluate 15-20 years from now when it’s time to change again. (Eastern MA)

At current or predicted future electricity/gas prices ?

I can imagine having solar and using partly that (instead of selling it back to grid for pennies) might've skewed that too

Our grid is plurality natural gas fired, so I’d expect them to broadly track for the majority of the lifecycle of this equipment.

A slate roof precludes advisable/economic solar installation, plus the major part of heating load is in winter (obviously) and in the 75% of the day that’s not 9AM to 3PM.

As a fellow owner of a slate roof I recently came across panels made to look like blocks of slate tile[0]. They look to be a bit less efficient than a traditional panel and I've not looked into the costs yet but it's nice to have the option! I imagine there would be similar products in your neck of the woods.

[0] https://www.gb-sol.co.uk/files/PV%20Slate%20brochure%20v2_3....

Those are beautiful; thanks for the reference! At the price of labor in New England, I kind of doubt those will have an economic payback either, but I'll do a little more poking around.

$20k sounds a lot to me. What peak power did you need (BTU/h or kW)? Have you shopped around for offers?

I researched and shopped it pretty hard (the latter to limited effect). Lots of companies do boiler swaps in ~3 hours with one plumber or one plumber and an apprentice/laborer. Only one company would even quote the air-to-water (which has its own dangers now and for 20 years of operation).

Changing from gas to air-to-water heat pump involves electrical work (inside and out), core drilling through structural brick walls, some landscaping work, much more plumbing work (both water and refrigeration), and more and more expensive equipment (way more piping, a buffer tank, a domestic water storage tank, and the indoor and outdoor units), plus the labor to install, inspect, and maintain all that.

Heating load on design day was calculated 78KBTU/hr. (Old boiler was ~60% efficient, 200KBTU/hr input and cycled easily on design days.) I think the true figure is likely just a bit less, but the exact figure turns out to be irrelevant for a gas combi boiler as it’s already sized large enough for the higher domestic water heating load. For a heat pump, sizing to load and using storage tanks is critical.

I really wanted to have the switch make sense. It wasn’t even close, even with several thousand in additional incentives.

Wow. An enormous cost indeed. I think you made the right choice, at least for now.

When climate becomes enough of a problem that governments start taxing fossil fuel instead of subsidizing it, the story may be different. But for now I would have made the same choice.

Yeah, I'm consoling myself that we're at least using 34% (Dec, 1°F colder this year) to 56% (Nov, 1°F warmer this year) less gas than same month last year, so we at least reduced our consumption significantly, even though it practically locks us into local burning fossil fuels for a couple decades.

The old boiler really was a disaster from an efficiency standpoint. 1950s General Motors (not a typo) oil burner, converted to gas with a single-stage [200K or 0 BTU/hr] burner, drawing combustion air from the basement, and sending 160°F-190°F water to the building and taking up an enormous footprint in the basement. Now has a 95% Bosch combi, drawing combustion air from the outside, using outdoor reset to send 118-136°F water to the building, and hangs on the wall taking up about as much space as two milk crates stack atop each other.

Our grid is ~40% natural gas anyway, so when taxes hit natural gas, they're going to hit heat pump users as well.

That's an interesting calculation you have there. We wouldn't want something bad to happen to it. My associates and I offer coverage against unanticipated rises in gas prices. We call this prote^h^h^h^h^h insurance.

More seriously, I can see how this might make sense in the US, assuming that US domestic gas production and politicians can keep the fossil fuels flowing, but the calculations have much wider error bars where I live. For me, US$20k over 20 years is a lot of nights not tossing in my sleep while I dream uneasily of tomorrow's headlines.

That's an interesting amount, since I assumed things are cheaper in the US. I live in Finland and we got an offer for my house to install an air-to-water heat pump system (with an existing radiator network, which I assume you have too with your old gas boiler) for 13 k€ total. Is your house very big or what explains the huge difference, since you quote it would have been $20k more than some lower price?

Not massive. ~2650sq ft, 2 levels plus a finished attic. 1920s structural brick (so limited and varied cavity, but good attic and roof insulation).

Boiler swap were $15-20K bids minus $1.2K in incentives. A2W was $42.4K minus $7.5K in rebates (with some uncertainty as to rebate payout, because they could require additional weatherization as a condition of the heat pump rebate, which wouldn’t be known until after project commencement).

I think the difference is we have one company in that market and they can do 6-8 boiler swaps for the same amount of bidding and installation labor involved in one A2W job, plus that gets them 6-8 customers on maintenance plans instead of just 1. I have a sibling comment laying out some of the (genuinely) more work it would take to switch to a heat pump: https://news.ycombinator.com/item?id=34352854. It was going to be "2.5 to 3.5 days" for the plumbing crew, a half-day of electrical, 4 person-days of trade helpers (landscaping and rough framing), outsourced masonry labor for the coring, and multiple inspections. That's a lot of mouths for my job to feed for them to get just one customer (and around $10K in equipment markup to cover overhead).

I don't blame them for bidding it a lot higher than a job that takes just a plumber and an apprentice 2.5-4 hours with no outsourced labor and only one inspection in order to get one customer (and around $5K in equipment markup to cover overhead).

My new (return air) heat pump that heats my whole house and provides all hot water is $6k. I expect a 15 year life. The only thing that could possibly be cheaper long term would be drilling a hole for ground heat, which would be around $15k with a similar pump and the difference being the whole.

Do you have existing ducts? I don't, but rather have existing radiators and piping for hydronic heat distribution.

The pump heats water and circulates it in the floors of the ground floor of the house and in radiators on the top floor. It also has an internal hot water tank for tap water, and a backup electrical heater.

https://assetstore.nibe.se/hcms/v2.3/entity/document/121339/...

I do have ducts for exhaust air from kitchen and bathrooms. That’s where the pump takes it’s heat from so it doesn’t need to work with outdoor temp air.

I love my heat pump. When it was -25C outside it was still performing with a COP of ~3. It is ground source - I have a large loop submerged in a large pond, so it is the temperature of the water (was low of 2C as read at the intake) that is important rather than the air temperature. It would likely be better in deep trenches (frostline here is 1.5m), but the installation cost in the pond was negligible, and meant i didnt need to tear up the garden.

How do you measure your COP? I'm having heat pumps installed now, and am interested in how everyone has this information at their fingertips.

My heat pump will say how much kWh of heat it has output (~2400kWh last month). I also have a separate electrical meter just for the heat pump that tells me how much electricity it consumed (~700kWh last month). I simply divide the heat output by the electricity consumed which gives me a COP of ~3.4.

I can connect the meter to the heat pump, in which case the pump will use pulses from the meter to calculate it internally, but i havent set that up.

I have no idea why it doesnt come with an integrated meter... seems like that would be easier tbh.

It's interesting. I wonder how they measure heat output.

not sure, but i guess its sampling the flow through and the delta-T across the condenser and doing whatever the relevant calculation is off that.

The lack of scale on temperatures throughout is remarkably frustrating. I am assuming Fahrenheit as the graphs indicate this but the content really should as well.

Yeah, I hate this. The title (with the words "cold climate"), the numbers (below 20 degrees) and then talking about Finland (where degrees are definitely Centigrade) just creates too much cognitive dissonance.

If you're writing an article about temperatures, and you want to use Fahrenheit, please actually say so, otherwise you'll have all your readers from 90% of the world's population looking at you oddly.

My understanding is that modern heat pump installations for colder climates come with an electric heat strip, a conventional heating element. It will take over when the heat pump can't work efficiently anymore. So the heat pump will continue to work. It won't be more efficient than a conventional heating element though - at the time of year when most energy is consumed. So heat pumps will lower overall energy usage, but not peak usage.

https://carolinacomfortsc.com/hvac/what-are-heat-strips/

While they can have these elements, heat-pumps in general have come a long way in their ability to get heat out of the air at cold temperatures. Mine is still over 160% efficient at -13F, with no loss of capacity.

Below that it'll still operate at over 100% efficiency, but capacity starts to drop, so some part of the heating load may need to be made up by other means (it's common to install a handful of cheap resistive heaters for that case, as they add a redundant system that can continue to work even if the heat pump is out of service).

> So heat pumps will lower overall energy usage, but not peak usage.

This would only be true if we go far beyond normal 'cold climate' temperatures for a long period of time.

I just had installed three Mitsubishi RW25 heat pumps, latest tech which works with efficiency factor of two in -30 C (-22 F), and still produce their nominal heating power of almost 4 kW in -20 C. I live in southern Finland so we rarely even experience such low temperatures. Very good ROI.

Independent test in Finnish: https://www.scanoffice.fi/wp-content/uploads/sites/11/2022/0...

Air heat pumps obviously are way less effective when the temps outside are negative. The ground heat pumps work better, but the installation costs are the barrier. The silly thing is that even on a sunny winter day an air pump uses a fairly cold air instead of some heated by the sun collector. From what I got such air & sun collector systems are complex to manufacture and maintain, so the more energy hungry air heat pumps dominate.

Here is a plan for solar air heater panels that is quite efficient: http://www.iedu.com/Solar/Panels/index.html

Quite sneaky how the article gives the price of electricity in cents per kWh, then some un-named unit for the price of natural gas (which is very cheap in the USA). The price per kWh is much less than the price of electricity.

It's interesting that every time this comes up, return air heat pumps are never discussed. It's always the AC-kind. Is there something about how ventilation is built in e.g. the US that prevents using return air for heating? Where is the air that's drawn from kitchens/bathrooms typically going in a reasonably modern US home?

Return air heat pumps? It's telling that I have no idea what you're talking about, when I just this weekend pulled the wiring for the brand new heat pump that's literally being installed at my parent's house as I type this.

We both have (had, in their case) a forced air natural gas heating system, with "cold air return" ducts which transfer air volume from the bedrooms, kitchen, etc. back to the furnace room so that the heating vents aren't fighting back-pressure. Air drawn from kitchens, bedrooms, living spaces, etc. goes back into the bottom of the furnace, where it's heated and returned to the house. There are two sets of ducts, one going away from the furnace and one going back to it. It's a closed system.

You can't pull heat out of air in your air return, then pump that same return air through a heat exchanger to make it hotter than before.

Sometimes, yes, air from the kitchens and bathrooms when you turn on the stove exhaust fan or bathroom fan is conveyed out of the house through a baffled wall vent by a PVC pipe (note that a sad number of bathroom fans eg. in old hotels and apartments, where getting ducts out of the building is impractical, are not actually moving air: they just make noise and don't go anywhere). But those dedicated fans are only turned on for a few minutes per day. Just about everything else is a closed system...older atmospheric venting water heaters and

One thing that I would be interested to see is a clothes dryer that was energy-aware; I've got a newer, reasonably high-efficiency gas dryer but it does dump a lot of energetic hot and humid air into the sub-freezing exterior in winter, which is replaced by cold air getting pulled into the house, and it pulls my expensive cooled air into itself in summer, heats it, and blows it out, to be replaced by pulling in hot and humid summer air.

Return (exhaust) air pumps just use the heat in the air that was being evacuated anyway. Requires only that you have ducts from those rooms that are ventilated (usually kitchen and bathrooms) to the pump, and from the pump out to ambient. It’s not a lot of ductwork. This is for older houses here which have no forced incoming air. Bedrooms/livingroom just take in fresh air directly from outside. A more modern home would have heat exchange between in/out air to move the heat from the incoming to the outgoing air.

Return (or exhaust) air pump: https://assetstore.nibe.se/hcms/v2.3/entity/document/121339/...

Those are cheap as hell. Handles all the hot water, space heating and ventilation in my home with a $5k device which has a COP similar to a wall unit + works when it’s really cold outside too.

It's strange to me that bedrooms/living rooms take in fresh air directly from outside. Wouldn't that incoming air be very cold and have super low humidity? And in the summer you'd have enormous amounts of hot, humid air coming in?

I suppose that in a way, American-style forced air is kind of like a heat exchanger between the return air and the intake air...except that instead of using a thermally conductive plate or heat pump to move heat from one mass of air to the other, it just redirects the return air itself with all its entrained heat energy straight to the intake.

I am a bit curious how the different solutions deal with issues of air quality. American houses often have small ~50W fans in the kitchen (over the stove, sometimes integrated with the microwave, called an "exhaust hood" and engaged only when the cooking gets smoky) and in the bathroom, engaged only when someone's showering and wants to remove the steam or defecating and wants to remove the smell. You often don't put cold air returns in these places, because you don't want those things to be immediately plumbed to the rest of the house, you put cold air returns in living rooms, hallways, and bedrooms. But that means you're re-breathing the same air over and over again. It usually passes through a filter in the furnace, but still... I think new builds with terrific air sealing often need a little 3" PVC direct vent to admit fresh oxygen.

The really old buildings obviously had no ventilation other than simply being not-very-sealed. Only a couple of generations ago there were still houses with single glass windows, there weren’t any moisture barrier film in the building shell, doors weren’t well sealed and so on.

The second gen with forced exhaust emulates the old self-draft by forced exhaust ventilation and that exhaust air has to be replaced by air that enters somewhere and since the air is evacuated from kitchen/baths it’s let in through all other rooms. Yes that air can be cold/dry and it’s also uneconomic if it’s -20C so these vents are adjustable so you can close them somewhat when needed. Heat exchanged air forces both from and to the building is of course an improvement over the from-only, but the ductwork required is much more complex so it’s mostly done in new builds. The great thing about forced exhaust only is if it’s combined with a heat pump that reclaims the heat so it’s not wasted.

As far as I know the rule of Thumb regardless of system is that all the air in the house should be replaced every two hours using only the base flow i.e excluding the kitchen fan. So air quality is ensured for both systems as they shift the same volume of air, but comfort and economics is better with the more expensive system (no freezing fresh air entering).

In US construction, a heat-recovery ventilator (HRV) would be used to mitigate losses from replacing indoor air with outdoor air. These are not heat pumps, but passive heat exchanges to transfer heat between the outgoing (stale) air and incoming (fresh) air. The HRV is commonly added as a dedicated, central loop to do air exchanges for the whole house, while the regular central HVAC system maintains a closed loop as described previously. A pair of fans pushes stale air out and draws fresh air in through the exchanger.

Tightly sealed houses will have ventilated "make-up air" pushed in to offset exhaust flows, to avoid creating a pressure gradient. In principle, you could also use an HRV with each exhaust duct for kitchen, bath, etc. However, in most houses these are separate vents to outside local to each room, not a centralized ductwork. To use an HRV you would need to add one to each vent location along with an intake and extra fan for the local make-up counterflow. It also seems like you would have to worry more about condensate and maintenance issues with pushing highly humid cooking or bath air through the HRV...

The kitchen fan duct in a Nordic house or apartment is separate from the regular ventilation. I assume thats pretty universal for fire safety reasons. It’s a 125mm or 160mm pipe with 50mm fire insulation using a fan in the hood or on the roof that runs only when cooking. But there is also a vent in every kitchen (ideally at the opposite end) which draws the regular exhaust air continuously (much slower and quieter). Only that vent is connected to the heat exchanger or exhaust heat pump. They must be separate because the kitchen vent should manage a grease fire and you don’t want the grease into the ventilation.

Similarly in bathrooms there is a vent drawing a base flow of air to the hrv/heat pump but it’s also common to have an additional direct exhaust e.g on an outer wall which only runs when needed.

So the ventilation system with heat recovery is only for the continuous ventilation. Then short term ventilation like after a shower or when frying meatballs is in addition to that.

I thought you were worried about optimizing the loss through the exhaust/extractor systems, i.e. the intermittent fans used to remove steam or bad odors by dumping conditioned air to the exterior.

With a central HVAC, there would of course be some kind of return to take from inside the house and send it back through the system again. I think others in the thread are taking it for granted that any system will be an inherently recirculating design.

Some modern houses might have return ducts in many or all rooms. But, it is relatively common to just have a few centrally located returns, relying on open floor plans and/or leaky interior doors to allow circulation from rooms back to the return vents.

For example, our ~45 year old house has a gas furnace with heat vents near the outside walls of each room, and air flows back through hallways to reach centrally located return vents on each level. The return vents are in a stack quite close to the furnace which is also centrally located.

It's -22C here this morning (-8f), and both of my heat pumps are working fine (currently 20.5C indoors). I have an LG, and a Fujitsu. The LG has an element inside the central air-handler as well, so if it gets too cold, you can switch that on to provide backup heat. I expected to need it last night, but the heat pump did fine without it.

What pisses me off about this article is how it keeps talking about "degrees" and about Europe, but then you find out it's F degrees and not C degrees if you look at the graphs.

Please use SI units, but in any event, please place units next to numbers!

Very confusing indeed.

Minor thing: Celsius isn’t SI either.

Degrees Centigrade is an SI derived unit, just like Joule and Watt

https://en.wikipedia.org/wiki/SI_derived_unit

They also don't give units for the price of natural gas.

Over the last 10 years we've had to replace our furnace twice, and happen to have both gas and a heat pump (a hybrid system). Each time, we had a different contractor do the installation...but both guys told us that they like to run gas below like 30 degrees. The second guy said he runs gas exclusively - no heat pump installed in his home. I asked what the primary differences were in terms of efficiency, and both claimed that temperature at the register is significantly hotter, producing more heat with less effort and therefore more efficiency.

I haven't done any scientific testing; the only data I have to measure the difference is my energy bill (which of course is subject to rate changes). But I have indeed observed that with gas, our bill is lower during the very cold months, and I'm able to see this because I have years of data on what we spend each month on energy.

I have a aux heater that kicks in when the heat pump can't keep up, and I have noticed this. When the heat pump is running, the air coming out of the vents is barely warmer than ambient. Definitely less than 70F. When the aux heater kicks in, the air is actually hot.

A side effect is that the heat pump needs to run a lot, because heating a house to 62F takes a long time with air that it 65F.

This[1] diagram from the article is really the crux of why many homeowners skip the heat pump option when fitting out a home.

Notice how the promised specs, a COP of 3 at 17F outdoor and rated power, aren't achieved by a single real user?

The real users get between 1.0 and 2.3 COP.

That means the cost of your system will be approximately double to run what the manufacturers specifications claim.

The government needs to step in and force companies to measure their heat pump systems in conditions more representative of a typical installation.

[1]: https://lh5.googleusercontent.com/05uL7FR8oHB3leKUvLABRMZTJ4...

> That means the cost of your system will be approximately double to run what the manufacturers specifications claim.

Wait, seriously? That's (a) disappointing, because I thought heat pumps were pretty great. And (b) you're absolutely right: it's misleading advertising.

Typically these systems underperform because they are tested in ideal lab conditions, but then the actual installation has lots of non-idealities (long pipes with lots of bends, dirt, dumb thermostats, wrong flow rates, poor airflow, blocked filters, things cycling on and off, etc).

The full report that the (uncited!) diagram is from is here: https://acep.uaf.edu/media/290488/Air_Source_Heat_Pump_Poten...

The report describes a few other heat pump models which do meet the advertised specs.

Thanks, that's reassuring.

Thanks for the link! I have Fujitsu which I run when outside air is above 40F. Looks like it gets an amazing COP of 5 to 6, far exceeding the spec. I have tankless hydronic heating using natural gas for most of the winter, but it couldn’t quite heat my house when temps dropped to 5F.

realistically considering equipment available today most people thinking about heat pumps in cold climates would be better served by geothermal systems than air source

How's your Finnish? https://cooperandhunter.com/split/files/docs/support_2019020... magazine review from 2019 I think. Says at -20F you still get around 3x COP energy ratio. On the other hand the air to air heat pumps they are testing cost three times as much as a regular one. Unfortunately they say the worst temperature is just above freezing where the air can still hold plenty of damp but quickly be cooled below freezing to turn the damp to ice... Cold but damp being the description of British winter. The American idea of winter air cracking with dryness and running a humidifier indoors doesn't really exist here. They are currently free of sales tax in the uk though. Tricky to work out which models are designed towards heating rather than cooling. Hopefull though but still begs the question if they are so great why are most people still buying night storage heaters and such? Just a lack of skills? Annoyingly they are only £600 for a decent japanese one and connected a £90 vacuum pump for half an hour, look at the guage to see if its holding a vacuum and then turn an allen key to release the gas. It looks not too hard but we are not allowed to buy them incase we pollute the enviroment with refrigerant, just out of reach...

In the US the department of energy is having a challenge to heatpump manufacturers to manufacture a heatpump that will work all the way down to -20F (-29C).

Both Trane and York have prototype models that meet this requirement and should be on sale in less than 2 years

Here is an article discussing it https://electrek.co/2022/12/26/us-companies-are-producing-he...

It would be nice if they step up their game. The US has been clobbered over the last 15 years by the Asian heat pump/mini split brands like Mitsubishi, Fujitsu, Midea, and Gree. Most of the myths in this article come from experience with crappy American heat pumps that are as technologically out of date as a cell phone from the early 2000s.

I have both a larger return air unit which provides hot water for taps and radiators, and a smaller pump/AC on the wall which doesn't need to work at all in winter, but is useful for providing AC on the hottest days. The AC style pump heats OK down to very cold temperatures but I'm not sure what the efficiency is at -20, probably not great.

A return air heat pump has no problem with cold temperatures because its not pulling heat from outside air, it's pulling heat from warm air that's sucked from the air about to be ventilated out of the house (what's drawn from vents in bathrooms and kitchens). So it cools it from say 20 to 0 deg and exhausts it on the roof, transferring that heat to the hot water system both for radiators/heated floors and tap water. This is similar to how a ground-heat pump works too. It also doesn't need to worry about freezing temps because the ground doesn't get that cold, especially with a deep enough hole.

Those two forms (return heat and ground heat, are probably 95% of the heating solution for single family homes in my Swedish suburb). Very few would heat a home with either anything combustible OR with an outside air unit. Many have them, but mostly like I do as a complement or summer AC.

I'd not recommend an outside-air heat pump for heating anywhere where it's regularly very cold. Much better to just set up a proper heat pump and connect it to a water based radiator system. You need to have some kind of ventilation in the house so no point wasting that heat by blowing hot air out the roof.

I don't like the article because it starts with a question that answers through a lot of jumps trying to essentially sell you the specific solution. Probably that is how they write articles in general from a couple others that I've seen but it would have been more fair to just answer the question in a simple way, yes because here are the specs sheets showing that

Expanding a bit more on my comment, the factor in sell stats from Scandinavia where home insulation is on another level and especially in Norway they just move away from fossil fuels in general - while they sell them elsewhere - regardless if for example EV batteries keep half the charge in winter time, just because they have money. Then the factor of house insulation in general, sure a much better insulated house can do with a not very efficient solution. And while they only touch a bit that every case is different, they don't discuss all the factors just the ones that can elevate the heat pump case. Doesn't it matter if this is a new installation with fan coils for example or a heating replacement case ? Electricity costs also, or this is a US specific sale ? and etc. etc.

I have a heat pump in New England, and it works but damn is it expensive right now. I think I need to upgrade to a bigger pump. My aux heat is kicking on semi regularly, and the heat pump is running it's reverse cycle pretty regularly.

I think heat pumps are an absolute no brainier. They work great for AC during the summer, and they heat my house really cheaply in the fall. I'm disappointed in my pumps winter performance, though.

Unrelated, but Florida Code requires landlords to ensure working heat, but not cooling.

Most heat pumps installed in Florida default to heating mode, and to switch to cooling mode a constant 24V needs to be sent to the heat pump's reversing valve. So if that valve, or voltage, ever fails when supposed to be in cooling mode you get cooked to 100F+ temps while you sleep, and burn out your heat pump while you're at it.

Most heat pumps made in the last 2 decades are computer controlled with a wide array of temp and pressure sensors. Stuck reversing valves do happen, but it's likely the unit will shut down due to an ambient outdoor temp, cool temps, or refrigerant pressures that are too high for heating mode.

Not much different from a gas furnace. If somehow the computerized safety controls went bad and the unit ran without the blower fan, it would quickly overheat and destroy itself and possibly catch the house on fire.

Luckily, these failsafe systems are well engineered with multiple redundancies. They aren't hacked together React apps.

Does anyone have experience choosing/installing/using a heat pump for both cooling and heating? The weather at our house gets just below freezing in winter and very hot (38C/100F) in summer. Currently, heating is via wood burner, solar thermal, and random space heaters, and we don't yet have a cooling solution. House has thick stone walls and a tiled roof (southern Europe).

Check out ground source heat pumps.

A one sentence summary of them is that they use the thermal mass of the ground to provide you the annual average temperature.

We have such a thing (some Mitsubishi model I will check later on if needed\) at home in Catalonia. Works OK, but the house despite being well isolated in general has a weak spot: dark external blinds. Without some external shading these warm up in no time, so the air between blinds and windows goes probably +45C or more. To combat this the heat pump in the air condition mode has to work way harder.

So a bit like with a Victorian house in winter where isolation is the key: one has to start with making sure that the house interior gets as little heat from sun in the summer as possible.

Thanks! Sure if you get a chance I'd be interested to know your model and when you got it. (We're in Portugal - Alentejo).

Does anyone know if they work in old houses?

We have a stone house built in ~1800. We have upgraded with insulation in the floors, walls ceiling, but of course it is still fairly draughty if it is windy.

It's damn expensive to heat, and have considered an air source heat pump, but always thought that it wasn't really a good idea for old houses.

There's no reason why it won't work, its just another (more efficient) source of heat.

It might work theoretically but that doesn't mean it should be done in many cases. Where I live electricity is nearly 3x the price of gas. While some heat pumps can achieve this in certain conditions it eliminates most of the affordable options which raises the question of how long are you willing to wait before a £10k-50k+ investment pays itself off?

They typically operate at lower output temperatures than existing systems. For example, swapping out a gas boiler for a heat pump will often require replacing all the radiators with much larger ones as well.

IIRC they're also less responsive. You might find yourself keeping the house at 18-20c all day rather than turning off rooms you aren't using. The effect is that you use more energy than you would have otherwise.

Right, it is decision that depends more on the economics of where you live and your usage than the age or construction of your house. Where I live, gas is not an option and there are subsidies to change over to electric and off of heating oil.

I lived in such a house once and it was permanently cold, even with heating left on all day. In this instance the problem wasn't just the draughts but also the fact that it was connected to the old standard sized radiators that never got hot, they were always just above tepid, at best.

The landlord will happily bore you senseless about how much money he's saved though.

They often operate at much lower temperatures than gas central heating. In older houses especially this will often require much larger radiators and/or UFH.

From my research a couple of years ago:

Replacing gas central heating with air source heat pumps was a waste of money, they're more energy efficient but the cost worked out the same due to gas being so much cheaper. If you have rooftop solar and batteries already and are overproducing electricity it might be a viable choice but without those you'd be spending a lot of money replacing radiators for no financial benefit.

Ground source heatpumps offered a decent cost saving but were extremely expensive to install. You also need space available to sink them or a lot of lateral space if you want to save a fair bit on the install. Before the energy crisis my estimates for breaking even on installation costs were on the order of decades.

> due to gas being so much cheaper.

I'm curious where you live. The OP suggested that gas and electricity prices vary a surprising amount throughout the US, and that gas is not usually cheaper than electricity, but is sometimes. They did suggest if you are in a place where gas is a lot cheaper than electricity, that might be the one thing to make heat pumps not cost effective, but that this was not typical.

I personally do not know much about this. (I don't even know how to know if my own gas is "cheaper" than electricity, since they are metered/measured in different units!)

I'm in the UK. Our gas is metered in m^3 but our energy suppliers typically bill and advertise based on the converted kWh price. My current prices for electricity and gas are 33.76p/kWh and 10.28p/kWh respectively. That's after a government price cap has been applied without it it's 49.15p/kWh and 14.00p/kWh

Based on those prices a heat pump would need to have at least an efficiency of 3.28 (3.5 uncapped) just to break even. Given that the total cost of installation is in the range of £3k-40k there really needs to be a compelling reason to retrofit an existing house.

Some of this is due to the vagaries of the UK energy markets. The outcome is that we often end up paying renewable providers of electricity based on the cost set by gas powered stations. At the moment that price has been grossly inflated due to profiteering, we're far less reliant on imported gas than mainland Europe.

I'd like to note that the price savings and break even point have probably gotten better compared to when I last checked. If we go back to much warmer, happier times - like September 2020 - I was paying 15.999p/kWh and 2.915p/kWh for electricity and gas respectively. Prior to that it was 14.150p/kWh and 2.920p/kWh. At that point I believe an air source pump resulted in a net increase in my bill and a ground source heat pump would have taken around 30 years to pay off. I should probably recalculate when things have settled down a bit.

Very interesting!

I wonder what leads to the gas/electricity price relationship being usually (but not always) inverted here in USA from UK. A good reminder that we think of these prices as being set by "the market", but there is so much policy and subsidy that actually effects them, probably in both/all countries.

Here my electricity is charged in kWh, but gas is charged in `therms`! I'm not sure if I can just convert one to the other to compare, or if differences in efficiency in various places matter, or what.

Let's see what I can figure out...

On my last bill, in Baltimore, Maryland, USA, from BGE. (I use standard BGE supply, I don't try to choose a different supplier on "the market", which is possible here in a confusing way)....

OMG looking at my bill, it's a mess. The first so many therms of gas were charged at a different rate than subsequent, then there's also a separate delivery charge per therm, then other fees... But let's just take my actual total bill and divide by therms... gives us $1.88813/therm... which I think google dimensional analysis tells me is $.0644/kWh for gas? Which is GBP 0.053/kWh for gas? Double what you are paying?

Electricity, doing the same with their crazy 5-part itemized bill and just dividing total charge by kWh used, I get $0.177/kWh. Which if I've done my numbers right is in fact 3x what I pay for gas, hm. GBP 0.15 -- same as you are paying?

I am confused and may not have done proper arithmatic.

OP suggests:

> In Connecticut, electricity costs a little more than $0.20 per kWh. Those same electrons cost $0.10 per kWh in Louisiana.

So my electricity rates are right smack dab in the middle there.

OP says of gas:

> In Florida the average price of residential natural gas is about $2. In Idaho it’s $0.65.

If those are therms, my gas rates are to the top end of that but within range: $1.80. Ok that makes sense.

Hm, so OP is suggesting at these prices heat pumps should still work out, which is not what you found...

> which I think google dimensional analysis tells me is $.0644/kWh for gas? Which is GBP 0.053/kWh for gas? Double what you are paying?

You're paying about half of what I am for gas and electricity, almost 1/3 of the unsubsidised price. I'm paying GBP 0.1028/kWh for gas and electricity is GBP 0.3376/kWh. We usually list energy in pence(£1/100) as it's a bit easier to read.

It's interesting that you have additional consumption based supply charges. We have an additional daily "standing" charge that's independent of use. Currently those are GBP .2256/day(GBP 93.294/year) for gas and GBP 0.4669/day(GBP 170.4185) for electricity.

> Hm, so OP is suggesting at these prices heat pumps should still work out, which is not what you found...

The ratio between electricity/gas prices has reduced since I last looked into it. Based on 2020 energy prices in the UK a heat pump would have been more expensive to run unless it had a cold weather efficiency greater than 4.85. At the time this necessitated a much more expensive heat pump which is probably where the 10k came from.

If we look at the Energy Saving Trust's current projections[0]. Someone with a relatively new boiler would expect to save £115/year. My energy provider offers a relatively cheap installation package starting at ~£3k[2]. It would take 26 years to pay off the air source heat pump at that rate. Their projections based on April's price data.

Many people require extra insulation and larger radiators to offset the reduced output temperatures of a heat pump. Radiators add an additional £200-300 each (£500+ if you're splurging) and a 4 bedroom family home will have a minimum of 6, more likely 8. If you end up spending £5000 overall it'd take 43 years to recoup the cost of changing your system.

On the bright side! If you're on an older boiler you could pay it off in under 10 years and if you're unfortunate enough to be on resistive electric heating, as far too many people still are, you'd break even in just over 3.

If we look back to March 2022 when energy prices were still inflated, Which[1] estimated that replacing your combi-boiler with a heat pump would cost you an extra £80/year. Should energy prices stabilise we'd expect to see the savings offered by a heat pump decrease. Which also estimates a much higher installation cost at £7,000-13,000. At the top end it'd take 113 years to pay for itself based on energy costs at what appears to be the peak of the gas crisis.

Ground source heat pumps are more efficient but the time to pay it off is similarly dire. The Energy Saving Trust estimates £24k to install one in a horizontal trench[3]. If you don't have the space or don't want bury a grid of pipework across your entire garden they estimate closer to £49k. They estimate a saving of £195/year. You'll break even in 123 years.

The issue with them is that they're a large capital investment that doesn't result in equally large cost savings. Until gas prices rise much closer to that of electricity, heat pumps will either cost more to run or will take longer than their expected lifespan to pay for themselves.

[0] https://energysavingtrust.org.uk/advice/air-source-heat-pump...

[1] https://www.which.co.uk/reviews/ground-and-air-source-heat-p...

[2] https://octopus.energy/get-a-heat-pump/#heat%20pump%20cost

[3] https://energysavingtrust.org.uk/advice/ground-source-heat-p...

> You're paying about half of what I am for gas and electricity, almost 1/3 of the unsubsidised price

Ah, maybe that explains it.

And that matches my assumptions about US vs UK and EU -- US makes energy really cheap for consumers.

That could explain the OP, the cost-benefit might make more sense with US energy prices? Or is that right, should it be the opposite? The OP seemed to know what they were talking about, do you think they were wrong? I'm figuring they were right for US prices but maybe not UK.

> It's interesting that you have additional consumption based supply charges.

So it's complicated, and has to do also with the fact that my state in the USA, Maryland, has a complicated "market choice" thing where you can choose your "energy supplier" from a number of different companies with different complicated rate structures (most of which float in some way, and change month to month). But of course you still get the gas and electricity through the same pipes and wires. So you still pay the traditional legacy companies for "distribution" to pay for the infrastructure, while (if you choose) paying different companies for "supply". then there are various other fees and taxes (some based on usage) on my bill that I have no idea what they are.

My impression is that the "supply choice" thing is all a neoliberal scam. The price structures are super confusing, and a LOT of people, especially poorer people who can't afford it, get really taken for a ride. Often there's a cheap "teaser" rate, then the rates balloon to something hypothetically "market-based" but who really knows where the numbers on your bill come from. I have stuck with the traditional/legacy supplier myself.

At least once a week people knock on my door (in a not very wealthy neighborhood), salespeople trying to get me to switch my energy supply. Except they don't say that, they usually are very misleading about what they are selling, trying to imply (or outright lying and saying) that they are from the government or the traditional utility company, or are here to "check that you've done things right on your energy bill" -- they never have written materials to leave with you or a brochure, just a patter. Which only reinforces my belief that it's just a giant market for scamming people. (I think the salespeople themselves often don't really know what's going on, they're young people desperate for work recruited for commission-based door-to-door and being scammed themselves!)

So USA -- cheap subsidized energy prices, but a system still set up to screw poor people and enrich scammy corporations (and screw the environment).

> And that matches my assumptions about US vs UK and EU -- US makes energy really cheap for consumers.

It's hard to judge, prices here spiked 3-5 times in two years; I'm pretty sure they more than doubled last year alone. I don't think the US was affected as seriously by the Ukraine situation. Government negligence has allowed a lot of price gouging by energy companies. Further incompetence has led to renewable suppliers being paid a rate based on the inflated costs of running a gas power station.

> That could explain the OP, the cost-benefit might make more sense with US energy prices? Or is that right, should it be the opposite? The OP seemed to know what they were talking about, do you think they were wrong? I'm figuring they were right for US prices but maybe not UK.

Cheaper energy makes capital intense investments a less sensible. As an extreme example, if your energy bills are only $50/year spending even $1k on a device that cuts your bills in half would be a poor financial decision.

The other major factor is the ratio of electricity to gas prices. It sounds like in some places they're nearly equal. Heat pumps are a much more sensible option in those places. If a heat pump is 3x as effective as heating with gas, 1kWh of electricity needs cost you less than 3x that of gas before you begin to see a financial saving.

Another is that UK homes are almost universally heated by circulating hot water through radiators in each room. Comments from others seem to indicate that these setups are typically more expensive than the air based systems typical of the US.

> My impression is that the "supply choice" thing is all a neoliberal scam. The price structures are super confusing, and a LOT of people, especially poorer people who can't afford it, get really taken for a ride. Often there's a cheap "teaser" rate, then the rates balloon to something hypothetically "market-based" but who really knows where the numbers on your bill come from. I have stuck with the traditional/legacy supplier myself.

Private energy companies feel like a joke. Cheap energy is fundamental to the health of the economy and the population's quality of life. Seeing as any kind of shock require government intervention, I don't see the benefit of allowing private companies to siphon off profit when times are good.

We have similar-ish systems. The majority of people are on a fixed tariff with top rate capped by the regulator. "Agile" tariffs allow people to opt in be billed at half-hourly market rates. If you can shift your usage to the cheapest hours you'll sometimes find yourself being paid to use electricity. In a stable market with battery storage and solar you can save a lot of money. During the crisis there were 2-3 months periods where people were paying 1-3x more than the capped rate though.

New refrigerants will make a big difference here. The main theoretical restriction is the pressure delta required to go from a low enough pressure to transfer heat into the system at a low ambient temperature, then to a high enough pressure to transfer heat out of the system at a high ambient temperature. That’s what causes the loss in COP at low temperatures—the increased work the compressor has to do.

It’s definitely theoretically possible. There are refrigerants that can do this now with a relatively low delta, but generally they are flammable, toxic, or have high global warming potential.

There are other ways around this like booster systems, but it becomes a $$$ issue at that point.

My dad builds houses in northern Ontario and heat pumps seem to be getting more popular on new builds. This is a place that regularly gets below -30C in the winter. The heat pump (usually a heat pump/AC combo unit) by itself doesn't work in these conditions, you'll always pair it up with another system like a natural gas furnace, or resistive heat electric.

My personal heat pump is an older unit, it works down to -10C then then forced air electric (resistive) furnace kicks in. That thing is pricey to run, so I also light up the wood stove at that temp to reduce the costs.

Would the resistive furnace would be about the same cost as running electric baseboard heaters?

I don't understand why anyone would be worried their heat pump isn't going to work in winter. I've never seen a heat pump installation that didn't include an emergency resistive heater.

It's not so much a worry as an efficiency thing. If your in a cold climate that needs resistive heat its a lot less efficient to burn natural gas at power plant at 50-60% then turn to heat with a resistor in your house, than to burn it in your house at 80-90% efficiency.

Thing about a heat pump is it basically turns into a resistive heater once it can't capture any outside heat, then you just have heat of compression.

This changes with a lot of renewable and nuclear power, but also heat pumps that can keep operate rating above unity in those cold temps really start making sense.

In my house we only have electric heat available. When it gets too cold, the heat pump no longer keeps up and the resistive heater in the furnace turns on. It is more expensive to use the coils than the heat pump. It is important to understand the environment it is running in to accurately predict your energy costs. The previous owner should have installed one that could run in colder temperatures.

Mine cuts off at 35F and I have to manually switch on the oil. I live where winter is normally below 35 at night. Very annoying system. (I didn’t pick it)

So there are two problems as I see it:

Firstly you see analyses like these where the author goes "see, heat pumps work fine in cold climates, look at these success stories!", and then proceeds to list a bunch of places that aren't particularly cold. People think Norway is cold, but if you look at Wikipedia then the average daily low for Tromso (a random northerly Norgewian municipality) in January is -5.6C, with a record low of -18C. Compare this with Calgary, a relatively southerly prairie city with an average low of -13.2C and a record low of -44C.

The second problem is that they say "don't worry, if it actually gets cold it switches to resistive heat!" The problem here is that the extremes absolutely matter, because this is when demand is highest. If a prairie province/state switches everyone to heat pumps, then your grid had better actually be designed for everyone to be using resistive heat for weeks at a time, because that's exactly what's going to happen when you need it most.

Yeah but there are other solutions as well. When these articles come up people seem so obsessed about finding some gotcha! and why it won't work for them in certain situations, its strange to me. Heat pumps are absolutely a better technology that will recoup their higher costs within 10 years for just about everyone (yes, not everyone... just about everyone). Find me a guaranteed 10% return in the market these days please, I will thank you enormously.

I am looking into this right now in the NYC area. My ~13 year old HVAC system has a refrigerant leak in the AC component. Heat pumps that work in the very cold are considerably more expensive. Except... I have a perfectly fine gas powered furnace that will likely last another 20 years, if not more. So we are going to leave the furnace in, only have it kick on if the temps get too cold and... done. This may not be true in all environments, but in the Northeast, electrical demand is far far higher in the summer than the winter.

Yeah, in the super cold north, maybe they aren't a home run- yet- but they get better every year, but this whole ludditeism and resistance to change is very strange for a place like HN.

I had a heat pump that seemed to work well above 10-20f (which was <10% of the heating days), but you could see the aux heat cost in your electric bill if you had a bunch of really cold days!

Surely your last sentence answers your question if most heat pumps come equipped with a backup heat source that uses a different mechanism.

Why wouldn’t people ask questions then about the limits of the heat pump?

Great system.

The advantage of running gas to homes is to avoid the single point of failure in the event either the gas or electric delivery fails.

Also, creating heat from electricity requires either a) massive amounts of sustainable energy b) nuclear or c) burning fossil fuels to create electricity, then sending it down the wire to become heat again. Under any condition except b), is massively inefficient. Trying to run a ton of electric heat off green power sources in a deep freeze would be a disaster.

> The advantage of running gas to homes is to avoid the single point of failure

I had a 10 minutes blackout today and my gas boiler heating radiators in all my house went off. I think that I'd need a UPS for the boiler if I don't want main power to be a single point of failure.

If you have gas and heat running to your home you will have one if the other fails. We just had a 24 hour blackout at my house. The fact that we had gas allowed us to remain in the home with hot water, stove and heat without too much inconvenience. One day without that wouldn't have been terrible, but other people nearby lost their electricity for days, which would be very hard without gas.

My point is that I would have no heat. I could cook and have some hot water because I could warm it up in a pot.

we switched to a heat pump last year and we’ve been mostly pleased. that said in the last cold snap when wind chill temps fell to -30 (we live in chicago) the entire system shut down! we talked to the installers and they said that when articles like this way “works down to -10” you have to understand that it’s the wind chill temp. also i’m sure there are other pumps on the market that would have faired better. we have a mitsubishi mini split.

What has changed in air source heat pump design that they work better in cold climates than they used to? I know they do, curious what the engineering is.

more powerful compressor, bigger heat exchanger, measures against snow and frost, better defrost implementation to avoid stop heating.

I’ve been wondering for a while now if it would be worth coupling a heat pump coils to the heat sinks of a battery, inverter or other building electronics to help offset the diminishing returns at the lower extremes.

The simplest example would be a heat pump with its own built in UPS style battery, but I also see it being built with coupling to a power wall style house battery.

In summer yes, but efficiency is not a problem then. In winter those are providing ambient heat within your property anyway.

This equipment would be installed outside, the difference being to position it near, or coupled to, the compression loop of the heat pump. When the pump is running, it draws from the battery, which will need to dissipate heat through its operation. Why not capture that heat and redirect it where desired.

In summer, you could decouple it and use standard separate heat dissipation mechanisms.

A black body catching some rays would give a decent boost (for part of the day at least) - https://www.youtube.com/watch?v=FtfaZMahSUU - just putting the split unit somewhere that catches the sunshine would probably be a non negligible positive!

Once we go down the heat extraction / transfer path some interesting efficiencies should crop up - any waste heat (higher than ambient temperature) exiting a property could reasonably be captured and used.

if carnot diagram is drawn, it will show nothing cheap. try to recall thermal dynamics taught many years ago. heat pump works well when the exterior temp differ not much from interior temp. Namely for places like Cal and Tex, still the winters need heating. if it is freezing temperature, much energy will be spent on the mechanical part. Literally an electric heater but maybe less efficient than an interior heater by your knee. Not very logically coherent. Recall the professor's words.

thermal dynamics is a very chilling subject, basically demysterifying fundamnetally and establish a solid view of engineering. Its experiments were repeated by millions of engineering students, the rules derived still hold firmly on earth so far.

The Carnot limit of heat pump heating from -25C (-13F) to 20C (68F) is over 6.5. That's 650% efficient. There's a lot of heat in our 'cold' air. If you're going to try to claim 'thermal dynamics' [sic] you should at least do the math on it first:

1 / (1 - (248.15/293.15))

They work pretty well, I live in the 2 hours north of Quebec City and it works most of the winter. Today is the first day that I turn it off as it's -22C outside, but as soon as it's -19C it could work again.

This tech has gone mainstream very, very quickly. PBS just ran a report on the pace of new installs in the US

https://youtu.be/RdzjrVwWz4o

More than half of all homes in Norway have had an air-to-air heat pump retrofitted. It is mandatory for all new construction. Case closed.

The writer is insultingly bad. In the first paragraph, they talk about temperatures dropping below -20, then immediately pivot to talking about -10.

A pump that works below -20 would be extremely interesting, IF the article was about that. It's not. It's standard heat pump salesbabble with catchy opening line, which happens to be 100% deceptive about what will follow.

It's so obvious and hackneyed, I want to sit the writer down and discuss their life choices with them.

> A pump that works below -20 would be extremely interesting,

Like this one?

https://www.mitsubishielectric.ca/en/hvac/professionals/fs-s...

Source live in cold country. Heat pumps work lovely till -5 to -10. Then most folks start using extra heating.

F or C?

Probably F. New heat pumps are usually good to -20C or -25C, which matches -5F to -10F. My heat pump is 11 years old and is good to -15C.

Mine is cheaper to run than my 97% efficiency gas furnace down to 5 degrees F.

Of course if you can have a in ground coolant loop, you can do even better.

> modern cold-climate heat pumps can heat a home efficiently even when the temperature drops below -10 degrees.

-10F is -23C.

Edit: I first put "-10 f to c" to google, and google converted it to "10 fahrenheit is -12 celcius".

-10F is -23.33C

Also 249.817 K

Also f'ing freezing.

As an electronics engineer, I always prefer millivolt to kelvin, so 21.528 mV instead of 249.817 K.

Special units for temperature are no more useful than yards or pints.

The unit here should be meV/k_B instead of mV btw (the latter is proportional to the temperature but doesn't have the unit of a temperature).

The convention used by SI to give the name "kelvin" to the unit of temperature and to set its value by giving a certain value to the Boltzmann constant is completely artificial and its only justification is to ensure continuity with a certain historical tradition.

A completely equivalent convention would be to give the name "volt" to the unit of temperature and to set its value by giving another value to the Boltzmann constant, numerically equal to what is currently named as the ratio between the Boltzmann constant and the elementary charge.

The fact that "volt" is also the name of the unit of electrical voltage does not matter. The name of an unit does not identify the physical quantity measured with it. For each SI unit, there may be many distinct physical quantities that may be measured with it. (This is a very desirable feature of the system, which avoids the proliferation of many arbitrary universal constants in the formulas.)

This is actually a fallacy not infrequent at computer programmers, to believe that storing the measurement unit together with a number is enough to unambiguously determine its meaning. In reality, also the measured physical quantity must be known. In many cases the intended physical quantities can be deduced from the context, but there are cases when you have old tables or graphs whose meaning is hard to guess, even when having the measurement units.

The unit eV (electron-volt, used for energy) does not belong to the SI, even if its use along SI units is officially tolerated.

The same is with the volt as a temperature unit. Like the Fahrenheit degree, it is not an SI unit, but it is possible to use a system of units that differs from SI only by measuring the temperatures in volt.

Such an SI alternative has two advantages over SI. One is that in many frequently used formulas a multiplication with an universal constant can be omitted. The second is that it is much easier to have an intuitive understanding of the effects of various temperatures when comparing their magnitudes in volts with the values of some voltages or of some energies expressed in eV.

Moreover, the use of the kelvin is not well justified by backward compatibility, because few people are accustomed to think about temperatures expressed in kelvin.

Replacing the Fahrenheit degree with the kelvin brings a computational simplification, but if that is the target, going directly to the volt achieves more.

But yards or pints are really useful units!

Like also the Celsius and Fahrenheit degrees, all such traditional units can be useful, but only as long as their use does not involve computations more complex than comparisons, subtractions and additions.

OP must have accidentally put in 10°F, which is -12°C.

These are "Split Systems", yes?

From a technical engineering perspective the -22F claim in the article is amazing. When I was a kid that number was +40F and we walked up hill both ways to school in the snow.

As cool it is as an engineering story, its AWFUL as a marketing article.

Heat pumps have the same problem as EVs, its been pounded into the general public for decades that some number isn't enough for some people and the number improves every year, every decade.

So the "general public" shitpost on the internet around the turn of the century that an EV that only goes 100 miles is useless and once someone sells an EV that runs more than 100 miles the entire world will convert en masse. Non marketing people do NOT understand that it doesn't matter that people only need 0.1X or 0.5X or whatever if you market a continuously improving number they'll ALWAYS demand they are not buying until that number improves to 1.25X or 1.5X. And as technology improves, we get there in a decade or two, but it'll be the same reluctance. I absolutely guarantee that 90% of the people on the internet will be disappointed in EVs in 2030 because range will only be 750 miles and if only someone would sell an EV with a range of 1250 miles THEN they'd buy it. It doesn't matter how many well intentioned people point out that the average driver only goes 30 miles a day or whatever. You don't fix a marketing problem by screaming math equations at people. Not most people. Actually works with engineers, sometimes LOL. You sell EVs buy demonstrating they plug in anywhere in ten seconds vs some poor bastard walking uphill thru a blizzard carrying a heavy gas can because he ran out of gas.

The other marketing problem with heat pumps is handled horribly by the article. Everyone knows they work like shit when its cold. Exactly when you want to be the toastiest they don't work. Its like marketing a spare tire for a car guaranteed to be flat when you need it the most. You can't gaslight people into wanting to be cold during a winter storm. The solution to this marketing problem is obvious. Instead of bitching at people that they would be holier than thou if they enjoyed being cold in the winter after spending a huge amount of money to avoid being cold, market (not sell) a heat pump model that has a 100KW electric space heater that requires special permission from the electric company to connect and flood video commercials of people in the arctic circle turning their houses into saunas by turning up the thermostat during a blizzard and they're all in towels and sweating while snow blows by the window. Everyone who actually lives up north knows its warm when it snows and cold when its not snowing but most of the people selecting a furnace for their house in Florida don't understand or care but they don't want to feel cold when its cold outside so they don't buy heat pumps, at least not now. After the new meme sets in that heat pumps turn your house into a sauna, don't buy a heat pump unless you want to sweat in the winter, the regular general public will start buying heat pumps. "Well I don't want all the hassle of installing the 100KW one, I'll buy a cheaper appropriately sized on instead"

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