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Comment by __MatrixMan__ | Hacker News Reader

I live in a colder climate where heat pumps are not popular. After talking with a number of HVAC people about this I was surprised to learn that despite being very similar to an AC system in principle, in practice converting an AC system into a heat pump system doesn't make economic sense--you end up just ripping one out and installing the other.

I don't fully understand why this is the case, but I hope that there's something that can be done to improve it. I'd love it if I could drive my AC unit as a heater for 95% of the winter, resorting to natural gas only during in the extreme cases.

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This persistent myth just needs to go away. People use heat pumps all over Scandinavia, including in the arctic circle. They are extremely popular there. They were early adopters of this technology there decades ago.

There are two popular varieties:

- Ground source heat pumps. Those work pretty much anywhere; just dig below the perma frost and you are good to go on the northern tip of Canada, Alaska, Norway, or wherever. Works great, ground temperatures tend to be very stable and it actually goes up the deeper you dig.

- Air source heat pumps. The expensive ones still work okish at extreme temperatures like -25-ish degrees C. Which is a reason these are actually more popular than ground sources even in places (e.g. most of Scandinavia) that reliably get such temperatures each winter.

I've been on zoom calls with two separate co-workers who are all bundled up because their heat pump can't handle the weather. It doesn't mean that the technology is inadequate in principle--probably their systems have some problem that competent HVAC installers know how to avoid.

But its an unfortunate fact that there are places in the US where installers that recommend heat pumps can't be found for 100 miles. It doesn't really matter if I'm technically correct about the merits of the tech in principle--if I can't find somebody to fix my system and my pipes start exploding, I've still made the wrong decision.

Also, heavy snows cause power outages in places where tree limbs fall on overhead lines. If gas outages happen... well I've never experienced one. Sure, if I lived in Norway I'd have a government that cares about updated infrastructure and I wouldn't have these problems, but since I don't, I do.

Given my local constraints, a dual-fuel system sounds pretty great.

Gas outages happened at a large scale in Texas when they were struggling with a bit of cold weather. When they needed it the most, it failed them. Coal plants also struggled. Both had challenges with supply of fuel and cooling water being disrupted. That kind of systemic infrastructure failures is on the rise in the US. There are all sorts of reasons why governance just isn't great in the US. But the reality indeed is that things are unlikely to improve on that front.

Which are all good reasons why the market for domestic solar, batteries, and heat pumps is so hot right now. The US is no exception to this.

Properly designed heat pump system includes backup for the coldest days - usually direct electric heating.

Most houses in Finland have a (decent) fireplace for heating in case of an electric outage.

> heavy snows cause power outages in places where tree limbs fall on overhead lines. If gas outages happen... well I've never experienced one.

If I lose power, my gas boiler does me no good. A gas boiler will use pumps (and likely a power vent). A gas furnace will use a fan and a power vent.

It's a lot easier to keep a gas furnace running on a generator for an extended period of time than a heat pump.

There are power outages in Norway too - though there are typically years between incidents, and years and years between incidents lasting a day instead of hours (with the exception of certain avalanche-prone areas where this happens much more often than people would like). So my home has a backup system - as do most houses. And that's a wood heater. But my house is so well insulated that it takes a day even in the coldest of winter before I actually need to use it if this happens. Newer houses are also quite much better than mine in this respect.

Air source heat pumps are super popular in Poland too, this winter it was about -20C for couple weeks straight and not had any problems, toasty house without any issues. The key is that the heat pump exchanger really needs to be huge(ours is taller than a person) to get the heat out of the air.

The myth exists because the US is probably 10-20 years behind Europe and China in terms of HVAC and insulation technology. I recently had some reasonably high efficiency heat pumps installed at my house, and I’ve been very unhappy with the low temperature performance. It doesn’t even get very cold here—rarely below 5F (-15C) and a record low of -8F (-22C). The heat pumps I got (recommended by the well-regarded local HVAC company) operate at just 40% of rated capacity at 0F.[1] Meanwhile, Chinese and Japanese-made inverter driven heat pumps will happily go down to -5F at 100% of rated capacity, and -22F (-30C) at 80% of rated capacity.

[1] You can of course get a much larger heat pump to compensate, but that leaves the unit way over-sized for cooling loads.

Can't you get backup heating in addition to a heat pump for the coldest days?

I live in FL and we have a backup resistive heating element that kicks in as needed. Mostly only comes on a few days in the year or for short bursts when there's a cold snap that the heat pump can't keep up with.

This is fine until everyone in your neighborhood has one and it causes a brown out. (Peak amperage for the heating strips on my heat pump are three times as high as for the heat pump itself at maximum cooling load.)

You can upgrade your home electrical service and the power company handles all that for you.

Sounds like the units you are describing don't have an efficient (read 'big enough') heat-exchanger which is why they aren't being effective in not-so-low temperatures. The temperature of the cold-side should not be below outside ambient temperatures if the heat exchanger coils are sufficient.

In other words heat-energy should be going into cold side of the heat-pump (even at a low temperatures) at the same rate as it is coming out the hot-side at high temperatures. Reduce the heat in, and you will reduce the heat out.

It’s a typical size for a heat pump in a US home: https://www.amana-hac.com/products/heat-pumps/18-seer-aszc18...

My understanding is that improved low temperature performance has something to do with varying the amount of refrigerant in the loop: https://www.mitsubishicomfort.com/articles/keep-warm-this-wi...

I recently saw a transport nerd claim that US and Canadian (though interestingly not Mexican) busses were substantially and objectively worse in build and ride quality than European busses, even when they share the same engine components.

Which I guess similarly explains a lot of weird conversations and people talking past each other where busses are concerned.

https://youtu.be/U3qeYRI34C8

In my local market, if you ask an installer for a heat pump, you get something from Japan or Korea. I’ve never encountered an American unit.

(I’m referring to normal air-to-refrigerant-to-air heat pumps. I know of a really weird system that is thoroughly American and an utter pain in the arse to replace because it’s specialized and undocumented. It’s quite loud, too, because it’s single-speed, and that single speed is waaaaay too high.)

Trane and Carrier are both US based and do heat pumps. They are more expensive than Mitsubishi or Daikin though.

Some (all?) Trane heat pump models are re-branded Mitsubishi units.[0] Not sure about Carrier.

[0]: https://www.metahvac.com/

The Asian brands make products for the US market—often through subsidiaries that were originally US companies, such as Goodman and Amana. Basically stuff that complies with US codes and standards, and that US HVAC installers can fix without learning anything new. Daikin makes a ton of stuff they don’t sell in the US. Owens Corning makes high density fiberglass batts you can buy in Canada but not in the US.

Sounds like they undersized your installation in order to quote you a lower price. The efficiencies of heat pumps are well documented as are the weather patterns in your area. So, they should/could have known better.

Two solutions to this problem:

1) get a bigger/better heat pump.

2) improve you building insulation and figure out where you are losing energy.

Ditto Australia.

We've been using 'reverse-cycle air-conditioners' for heating in Australia for decades. I'm puzzled as to why there is any debate at all on their use for heating. A heat-pump is far more efficient for obtaining heat than direct resistive heating using electricity.

Many houses here use no other form of heating at all. And then at the press of a button, we get cooling in summer too. What's not to like?

* I also have a heat-pump condensing clothes dryer. The overall heat thrown out into the room is extremely low. The hot-air comes out the hot-side of the heat-pump to dry the clothes. The warm-moist air then passes over the cold coils, condensing out the water from the clothes and returning the heat to the cold-side of the heat pump which then pushes that heat-energy out the hot-side, producing more hot air to complete the cycle. I've had this Miele heat-pump condensing dryer going strong since 2009 - 14 years.

Yeah, as a Kiwi, watching all the debate happening here is just super weird.

Meanwhile, I'm annoyed that heat pumps that dump the waste heat into the hot water cylinder aren't standard.

It's just the Yanks that have subsidised natural gas in many states, and a messed up energy infrastructure that gives electricity prices in the same range as what we have in Europe while being at war.

I was trying to find heat pump adoption rates for Europe and US.

Seems like its still pretty low in Europe outside some northern countries. Germany is less than 2000/100000 people.

https://www.theecoexperts.co.uk/heat-pumps/top-countries

Meanwhile this link says US has a 15% adoption rate across all income groups. That seems higher than I expected.

https://energypost.eu/u-s-heat-pump-adoption-is-evenly-sprea...

Is there a better source on heat pump adoption rate in Europe and US?

Not a source, but it's more common to have heat pumps in the southern States where winters aren't that bad. I'm born and raised in Arizona and they seemed to be common in houses after the 1973 energy crisis. My grandparents house in Tempe, AZ (was built in like 1950's) did no have one. A house I purchased in central North Carolina had a heat pump. I'm now around Washington DC area in Virginia, and we has gas. I think a simple explanation is that natural gas is almost a by product (certainly from landfills, which is how most USA disposes of trash) and is very cost efficient. Also the energy crisis changed the outlook of house building. I hope that helps explain it some, sorry I don't have any concrete facts I'm typing on a small keyboard.

I've seen heat-pump base water heaters, but never a clothes drier. That sounds interesting. Now I have something new to research, thanks! Personally, I'm always curious why there isn't a more unified heat-exchanger system built into the structure of a house. HVAC, Water, Refrigerator, they all need to move heat from one place to another, why not work together?

I've tried to make the idea work in my head many times but my conclusion has been that I don't think there's quite enough co-incident demand for heating and cooling in the average house. For example, yes, I could generate all my domestic hot water from heat from air conditioning in summer, but in winter I need to be able to generate it plus heat the house, so I need enough capacity to generate that heat from the outside air when I'm not using air conditioning (so I don't save on not needing as much capacity), and the efficiency gains probably aren't worth the extra complexity.

For applications like commercial buildings, public swimming pools, industrial sites, etc. can (and increasingly do) definitely benefit from that kind of combination though.

I think the big issue is the different "tuning" for each heat pump system. For example, a heat pump water heater needs a different maximum temperature than an air conditioner, and has much different cycling behavior. This leads to very different design decisions, including refrigerant choice, pressure, compressor type, whether the refrigerant loop is even serviceable, etc. (Some appliances operate at a refrigerant pressure so high that they require being fully assembled at the factory, which would be a non-starter for a manifold system like we're discussing.)

I think this might eventually become a thing once science gets us far enough that there's an "obvious" refrigerant choice for most applications, but we definitely aren't there yet. There are hundreds of different kinds that perform better or worse in different applications.

AFAIK all of the big commercial systems that do multiple different types of heat transfer use water to do it, thus bypassing the entire refrigerant selection issue. Right now the most advanced we can do is VRF ("Variable Refrigerant Flow") systems that can individually select air handlers for cooling or heating (i.e. move the heat from one room to another). These are still commercial units and not really available for residential installs.

There’s a reason new houses get built with geo based heat pumps in Finland.

This enables your hot water heater to use the same circuit to heat water - that decreases your hot water bill to around a third, even in winter as the necessary heat isn’t taken from the indoor air but from the ground.

Heat pump dryer system is state of the art for efficiency. I saw some complains by American that it takes too long time for drying, but I don't know why they need to dry things so frequently.

If I’m doing 3 loads of laundry for the family, I don’t want a 2.5-3 hour dry cycle to make laundry take all day (or make me do laundry of half the days of the week).

I don’t want a 2.5-3 hour dry cycle

??? That's excessively long. Our heat-pump dryer takes about 20-30 minutes to do one of our loads.* The dryer invariably ends up waiting for the washer to finish.

* Our loads aren't excessively tight in the machine. You have to allow room for the clothes to tumble loosely thus allowing lots of surface area for evaporation.

I quickly googled for “how long does a heat pump dryer cycle take” and got several answers in the 2.5-3 hour range, which is long enough to provoke complaints.

Obviously, if every heat pump dryer took 20-30 minutes, you would not hear complaints about that (that’s much faster than my gas dryer).

Power-input. US dryers would typically work on 110 volts mains. Those similar dryers in the EU or Australia are working on 220 volts mains. Took me a while to click on why the great differences in working-times. 15 amps wiring in the US means 1650 watts, the same wiring in EU is 3300 watts.

That's not it. Electric dryers in the US are overwhelmingly 240V and on a 30A breaker. At 80% of rated, that's 5.7kW available. (Gas dryers here are typically on a 120V, 15A circuit.)

Every heat pump dryer I looked at on the home center's website is 240V. (Edit: I found one Miele on another home center that was a 15A@120V.)

I like mine, but it has a small capacity compared to a standard dryer, and we find that over time water slowly condenses inside of it, so we have to drain it a couple times a year to stop it from shorting its control panel. Not 100% if it's design flaw, micro leak, or what. 8 or 9 year old LG unit I think.

I was thinking about this anomaly yesterday. Then I remembered that most US electrical outlets are at 110 Volts instead of the more usual world-wide standard of 220 volts. So most stuff in the US is under-powered by EU or Australian standards. Being under-powered, it would take longer to dry your clothes.

(That's also why they don't seem to use electric kettles in the US commonly as is normal in 220 volt countries)

Yes. Although I have noticed that some people here in Australia go from the belief that "air conditioners use a lot of electricity" so therefore have the misconception a (resistive) electric heater must be cheaper to use than the reverse cycle AC (heat pump). So there is a bit of an education gap even here where they are quite ubiquitous!

I also do want to get a heat pump dryer (it's next on the list after my recently installed heat pumper hot water system), but I don't have quite enough space in the laundry and apart from two or three wet weeks a year I'd mostly only use it to fluff up towels (which is why I don't have a dryer at all at the moment)...

> have the misconception a (resistive) electric heater must be cheaper to use than the reverse cycle AC

You'd think costs would educate. Do people not talk about living expenses much?

Electrical bills come every three months. ALL electricity use is lumped together. So it's a bit hard to disect out what each usage-type is costing, unless you use one of those meters and study up average use over a period. Even then, some things like water heating and even aircons, are directly wired into the mains switchboard, so you would need an electrician to separate out those circuits for measuring. So it just doesn't happen.

I switched in New England when my freon system hit end of life. I wouldn’t recommend doing it beforehand, but as a replacement it’s been incredible. All the ductwork and infrastructure largely remained the same. Pulled out the furnace, evaporator coils, and compressor of course.

It cools better than the old system, and the fact that it runs longer instead of in short bursts means it regulates humidity way better too.

For heat we did go dual fuel, which means the backup heating element uses gas, since we already had the line. This works really well in a cold snap where temps drop well below freezing.

Fellow New Englander here. We had a 4 unit heat pump system installed a few years ago, replacing a bunch of window air conditioners. Not only is it a vast improvement over the window ACs in terms of ease of use, sound levels, comfort, and electricity use, it has become our default heat source in the winter as well, greatly reducing our natural gas bills.

There's no reason you couldn't just switch a couple valves out in your AC and perhaps change the refrigerant to make it into a serviceable heat pump. However, you'd need to retrofit controls/electronics, which I don't think most HVAC technicians would know how to do. It's also not advisable to attempt to DIY something like this because it is very easy to accidentally vent the refrigerant, which is a very potent greenhouse gas.

Right. It's a problem best confronted by the AC manufacturer. Except they have no incentive to do so (because if they don't, they get to sell an entirely separate heat pump down the line). Which means it's perhaps a problem for the regulator.

There are tax breaks involved with installing "energy star" rated equipment. Perhaps we ought to start witholding the star from AC units that are not easy to convert to heat pumps (and from thermostats, etc, which are not ready to handle the conversion).

I think that would be an excellent regulatory solution. You should write to your representatives. Since heat pumps are getting a lot of regulatory attention, it might actually get considered.

By the time you do that, you might as well also put in a variable speed compressor and a variable speed fan, at which point there’s not much left.

(Seriously, where I live, you will likely pay $1k or slightly more to drain and refill the refrigerant. The hardware for an entire modern heat pump, indoor and outdoor components, is maybe $3-4k. Is it really worth it to drain an old existing unit, cut the pipes, add a reversing valve, retrofit in the controls, pressure test everything, deal with the fact that the outdoor unit (formerly the condenser coil) will start producing copious amounts of condensate that the manufacturer and installer did not anticipate, and refill the system?)

This is because HVAC companies wildly overcharge. It does not take $1,000 worth of labor to drain and refill refrigerant, but it does take a qualified technician, and there are not enough of those.

That’s absolutely true. But the same problem would exist, much worse, if everyone started modifying their old A/C systems to turn them into heat pumps.

To add to the list of why this whole idea seems dubious: a conventional air conditioner operates with its evaporator coil at a balmy 50F or so. If you reverse it, the outdoor coil will become the evaporator, and it will operate below freezing if it’s cold out (even if the outdoor temperature is a bit above freezing). As a result, condensate can form and freeze on the coil.

This is entirely manageable (any modern heat pump can operate in decently chilly conditions, and heat pumps equipped for low temperature operation can operate in very cold conditions), but I expect that at least some engineering is involved.

I live some 5 hours north of Montreal, we have few days at -40C and wall radiators (not sure about the name) are needed, but for most of the winter days we use the heat pump to heat the house (-21C and up). Some members in my family work in AC/Refrigeration industry and all of them have thermo pumps, which make economic and ecologic sense. On the other side I don't know about AC/heat pump replacements as it's not common to have AC for the just a handful of days that could be very hot.

Colder climate is exactly where you want to use heat pumps. The numbers for Norway in 2022 (https://www.novap.no/om-varmepumper) is 58% of Norwegian homes (houses) have a heat pump installed, 34% in service industries, 8% in other industries. For homes air-to-air dominates (more than 90%). And since then this has just increased even more (and older heat pumps are being replaced with newer and better ones as well).

As an aside, many have commented on the claim that heat pumps make more sense with a well insulated building, arguing that it should be the other way around. The reason that you do want a well insulated building is simply that air-to-air heat pumps are limited to typically less than around 8kW heating capacity, and with a well insulated house you can heat a large area with that, with bad insulation you can't, and you would need a much more expensive type - typically not those sold to home owners (or buy several pumps, exploding the costs). In addition to that, a heat pump is more efficient when it doesn't have to run at maximum capacity. The heat pumps sold in the Nordic countries are typically around $3000 including installation. And they're highly efficient.

The thing is (especially where I live) I'd still need a gas furnace. We regularly see -20F to -40F in the winter. While the 95% scenario sounds great, in practice still needing gas means we still need all the gas infrastructure. From my understanding natural gas burns pretty clean. The problem is leaks in infrastructure and drilling, which isn't going away because I buy a heat pump.

Although natural gas is "clean" compared to, say, coal, the advantage of a heat pump is that it uses less total energy than natural gas. That means it would be more efficient to run a heat pump off a natural gas power plant than to burn natural gas to heat your home directly.

Where I live, you can bank solar credits. If you cash them out you get the "wholesale" energy price for them (much lower), but if you spend them on electricity then you've avoided paying full price for that electricity. So if your system produces more than you consume, you've got this free energy budget to spend--a budget that applies to heat pumps and not to gas furnaces.

People's AC summertime electric bills regularly get into triple-digits - it's not uncommon to hear someone with a moderately sized home having a $200-400 electric bill in the summertime.

However, even in the midst of winter, gas heating bills rarely climb above $100 monthly.

What am I missing here? It seems a heatpump, while more efficient, will cost significantly more to operate. Natural Gas is cheap... and clean enough.

It's actually difficult to say what the cost would be if everyone switched over. The reason is that natural gas is subsidized, both on the production side (at least in the US, which wants energy security) and on the consumption side (because it's politically unpopular to let people freeze to death). Of course, electricity prices are also affected by subsidies. Figuring out the true operating prices would require some research. However, it remains true that, in terms of greenhouse gas emissions, it is usually preferable to heat a home with a heat pump than by burning gas directly (there exists a temperature below which any given unit will become less efficient than burning gas, but unless you live in a place where this temperature is common then heat pumps will still come out on top (and the fact that residential gas lines are notoriously leaky and basically just venting nonstop into the atmosphere makes the calculation even more favorable)).

It seems to me, there is no future where a heatpump can be the only source of in-home heating then.

1) Natural Gas is vastly cheaper in most/all of the US.

2) Homes still require an alternative heating source when temperatures drop to low levels (coincidentally when people need heating the most).

So, even if a heatpump is technically more efficient in terms of emissions, the technology does not solve all of the problems it's attempting to replace. Additionally, Natural Gas is vastly more clean in terms of emissions than some other alternatives still used around the country.

There's no way the average home is going to stomach 2-4x more heating expenses on average without some real tangible benefit (hand-wavy emissions numbers don't factor into the average homeowner's decision making).

I must be missing something here...

> It seems to me, there is no future where a heatpump can be the only source of in-home heating then. > > 1) Natural Gas is vastly cheaper in most/all of the US. > > 2) Homes still require an alternative heating source when temperatures drop to low levels (coincidentally when people need heating the most).

> ... > I must be missing something here...

Yes you are, your natural gas subsidized, i.e. government handout, i.e. you're not paying the real market cost.

Second, heat pumps do not have issues with cold temps, unless you're at like -40c. They're used all over the nordic countries - including above the arctic circle.

Your energy grid is shit, which is why your electricity price is so high.

> Yes you are, your natural gas subsidized, i.e. government handout, i.e. you're not paying the real market cost.

> Your energy grid is shit, which is why your electricity price is so high.

Adding a heatpump solves this issue, or makes it worse?

Heat pumps power consumption can be modulated by energy providers and improve grid power stability.

In Germany you get way cheaper electricity prices if you allow this.

I am not aware of any such system in the US.

What do you mean by "modulate"? Your utility provider decides how much heat your home gets? That's a very strange concept.

No, they decide how many energy the heat pump currently uses for heating.

That means they control how much heat you get. Otherwise, they would always run in a more efficient/lower-energy demand mode... think about it.

Its only for a restricted time frame

Heat pumps might work at -40c, but all the efficiency gains are lost and it's going to cost a fortune.

The best one reaches 1:1 when approaching -35C, which means that they're as efficient as resistive heaters. So you save nothing in electricity costs, and if all your days are that cold then the $3000 you invested in the heat pump is wasted (that's how much a quality pump with installation will cost you in the Nordic countries - it seems to be much more expensive in North America, at least that's what the comments appear to indicate).

If you have warmer days now and then then you'll start saving money, and eventually it'll pay for itself. Where I live (cold winters), the cost was covered in only two years.

2-4x seems like a stretch, and would only apply in areas with very high electric rates. My last house was heated with a builder-grade heat pump (HSPF around 8), and my winter electric bills were around $150-200/mo. My current house has natural gas heat, and similar level of appliances/EVs/lighting, and winter bills electric bills are around $100/mo. This is the same town and the electric rate didn’t change, so the net cost of heating my old house with a heat pump was only $50-$100/mo. Meanwhile my winter gas bill in this house, subtracting baseline summer usage, runs more than that.

The only backup heat I had with the heat pump was electric resistance heat, which I needed to use only once or twice each winter for a few hours at a time.

You can also use resistive heating (like baseboard heating or space heaters) as a backup for the heat pump when it's too cold out. They're expensive to run off the grid, but if you have solar power and battery storage (for operation at night), they're essentially "free".

Obviously you wouldn't install solar panels and a battery just for this, otherwise it's very much not free, and probably a lot more expensive than burning gas. But if you already have the solar+battery install, and have enough capacity, it could even be cheaper to operate than a gas furnace.

You’re talking about the future but only consider the present. You’re one government decision from your calculation to have an opposite result. Estimating probability of any such decision (ban on fracking, tax incentives, etc) is the hard part.

I'm with you here. I replaced a gas water heater with a hybrid water pump and I'm paying more for my troubles. The thing is, I do plan on installing PV panels in a few years--I can't generate my own gas so once I make that happen, I'll be a happy camper.

That was my plan; install solar panels and then slowly switch things from gas to electric as they need replacement. Unfortunately solar installer I was in contract with canceled on me for seemingly-bogus reasons, and I didn't have time to find a new one before California's new, unfavorable net metering rules went into effect.

Most hybrid water pump heaters do not fully use their heat pump by default - their should be an "Eco" or "heat pump only" setting somewhere on your device which will make it much more efficient.

I'm fairly certain we're near - or even past - the point where burning natural gas to run a generator to power a heat pump will use less gas than burning the gas directly for heat.

Perhaps you live in a warm climate? A heatpump (or heatpump + gas for a very cold climate) should cost always cost less than gas

You need a backup heat source, but it doesn't necessarily mean you need full infrastructure of gas lines, ducting, and gas furnace. You could have an electric backup connected to ducted heat pump (e.g., non-efficient, pure electric) or could use electric strip heating, electric portable heaters, wood stoves, etc.

We have electric baseboard. It would cost hundreds more per month to utilize something like that instead of gas when it is -30F. In fact if we just leave it on over night a single time we notice it on our bill.

They make heat pumps with backup gas systems now.

Replaced our entire system (furnace, a/c) mid last year. Heat pump with backup oil for colder days.

We cut the amount of gallons we used by over 50% compared to last year. Sure the oil infrastructure is needed to get it delivered (I wish we didn't need it) but I'm very happy that our heating (oil+electricity) bills are so much lower, even with the increased oil prices.

We went with a mid-range system but now I kind of wish we sprung for the "Cadillac" version.

I suppose this would be true if gas is expensive where you live. It's really cheap here, our heating bill is like $80/mo in the coldest of months for a 3k sq ft house. A heat pump even with the efficiency gains would be on par with that (unless we jumped into solar, which I have considered).

Converting an A/C to a heat pump is a bit like upgrading an old Lenovo laptop to a modern CPU. It’s surely doable, and the parts are unlikely to be terribly expensive, but as a practical matter it’s pretty specialized and no one does it.

What you do is wait for the A/C to hit end of life (or end of efficient life if new systems are enough more efficient) and replace it outright.

(I once got a quote, in an expensive market, to add an A/C to an existing furnace and, separately, to remove the furnace and add a three-head multi-split heat pump. The two quotes were almost the same price. The equipment is not especially expensive.)

It's a $300 part that allows swapping the direction of heat flow. This tiny upfront cost is enough to block tons of good practice.

Nate the House Whisperer is a guy who has been trying to build a new generation of HVAC practice, and though he says he's usually a libertarian, he advocates for adding a tax to AC-only units that would eliminate this price difference (or some similar practice, I forget the exact details...)

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