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Comment by VWWHFSfQ | Hacker News Reader

A heat pump just makes no sense whatsoever for me in my northeast town. The electric bill alone would outpace the old propane bill, not to mention installation.

And it won't even work during some of the coldest winter weeks when you _really_ need it to work.

Maybe I would consider it if I was in, like, Nevada or somewhere.

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The notion that heat pumps don’t work at low temperatures hasn’t been true for years. I think you may be surprised to find that just about any heat pump you look at has good efficiency down to very low temperatures.

Define low temperatures.

Mine struggles if it gets below 30, and might as well not exist below 10. They're not great at low temps.

I’m not sure what yours is but it doesn’t sound appropriate to your application.

Mitsubishi hyper heat is indicative of a contemporary inverter design - 100% efficiency to -5f: https://www.mitsubishicomfort.com/articles/mythbusters-heat-...

100% efficiency is terrible for a heat pump. Electric resistance heat is 100% efficient.

I should have said 100% performance. COP is typically 3-4:1 with mitsu

Typical seasonal average? Sure.

At -5°F? Hell no!

At +5°F, they rate their own equipment to have a 2.0 CoP.

https://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.c...

Here's a Trane/Mitsubishi unit that has a COP of (at least) 3 at -13F/-25C:

* https://ashp.neep.org/#!/product/156605/7/25000/95/7500/0///...

An LG unit with 2.4 at -4F/-20C:

* https://ashp.neep.org/#!/product/29688/7/25000/95/7500/0///0

Searchable database of cold climate air source heat pumps (ccASHPs):

* https://ashp.neep.org/#!/product_list/

Correct (and thanks for the link to that unit).

Though it’s worth noting that that first 2 ton rated unit is putting out 0.5 tons (6k BTU/hr) at that temp and rating.

That’s not going to be particularly helpful for a structure that needed 24k BTU/hr during warmer temps, meaning the owner of the unit is likely mixing in a lot of 1.0 BTUs to meet the heat loss at -13°F.

> Though it’s worth noting that that first 2 ton rated unit is putting out 0.5 tons (6k BTU/hr) at that temp and rating.

I just did a quick search for "all" units and sorted the result list/table by COP@5F. If one was actually shopping/designing a solution then a more nuanced search criteria would be used.

Further, you'd probably want to do a (US ACCA) Manual J calculation to first determine how much energy is needed (j = joules)

* https://www.youtube.com/@HomePerformance/search?query=manual...

Then the (US ACCA) Manual S (select) to figure out your equipment:

* https://www.youtube.com/@HomePerformance/search?query=manual...

One can lookup the 1% (or 0.4%) of coldest/hottest days for your area, which would help determine what one actually has to typically worry about:

* https://ashrae-meteo.info/v2.0/

* https://www.airequipmentcompany.com/2021/what-does-design-da...

I've got one about 8 years old, and it does just fine down to 0°F (it hasn't gotten colder than that here). It doesn't even have any kind of auxiliary heat.

It's fine. The only difference when it's super-cold is that the air coming out of it isn't as warm, so the heating cycle stays on for a longer proportion of the time. But it keeps it 70°F inside no problem at all.

That's one of the older style units. Starting in 2007 when Mitsubishi introduced their "Hyper-Heating Inverter" heat pumps, and continuing with Fujitsu and Daikin following with similar technology in the 2010-12 timeframe, and others a few years later, heat pumps got way better in the cold.

Mitsubishi's maintain 200%+ efficiency down to -4℉ (-20℃) and 150% down to -22℉ (-30℃) [1]. Only a few towns in the continental US get below that, and even those aren't going to get cold enough long enough to make it worth it an an all electric home to switch to your emergency electrical resistance heating.

Their capacity doesn't start dropping until you get down to 23℉ (-5℃), dropping to 76% at -13℉ (-25℃).

[1] https://www.coolingpost.com/world-news/study-proves-heat-pum...

> Mine struggles if it gets below 30, and might as well not exist below 10. They're not great at low temps.

What percentage of the (US) population gets temperatures like that? That's generally mostly IECC Zone 7 (though cold snaps in Zone 6) can happen:

* https://basc.pnnl.gov/images/iecc-climate-zone-map

ASHRAE—an HVAC organization—has data on the coldest and hottest days for areas so that you can design things for the coldest or hottest 1% of the year (4 hottest/coldest days):

* https://ashrae-meteo.info/v2.0/

I think that if you have an older, leaky/ier, less-insulated house you may need to 'brute force' heating your (probably older) domicile. But if you have a <4 ACH@50 air tightness, and reasonable insulation levels, a good portion of the US population could make do with a heat pump.

Mitsubishi publishes data were they have 100% heating capacity at -15C, which some models being 100% at -20C and -23C:

* https://www.mitsubishielectric.ca/en/hvac/home-owners/zuba

At -25C they have 80% capacity:

* https://www.mitsair.com/wp-content/uploads/2024/10/MEM-20240...

> What percentage of the (US) population gets temperatures like that? That's generally mostly IECC Zone 7 (though cold snaps in Zone 6) can happen:

A lot? e.g. Chicago gets it every year

>>> Mine struggles if it gets below 30, and might as well not exist below 10. They're not great at low temps.

>> > What percentage of the (US) population gets temperatures like that? That's generally mostly IECC Zone 7 (though cold snaps in Zone 6) can happen:

> A lot? e.g. Chicago gets it every year

[citation needed]

Per historical weather data:

https://ashrae-meteo.info/v2.0/index.php?lat=41.960&lng=-87....

It is warmer than -16C/3F at Chicago (O'Hare) for 99% of the time (i.e., except for 4 days a year), and warmer than -18.7C/-2F for 99.6% of the time (2 days).

ASHRAE are the folks that publish the heating/cooling standards that are used in building codes for estimate heating/cooling equipment capacities (Manual J) and selecting the right equipment (Manual S).

Here's a PDF with a lot of locations in the US and CA (and other countries further down), and if you look under the "Heating DB" column, you'll find very few US locations that have -30F under the 99% (or even 99.6%) sub-columns:

* https://www.captiveaire.com/catalogcontent/fans/sup_mpu/doc/...

So unless you're in AK, MN, or ND, long runs of temperatures colder than -20F/-30C don't happen too often. Of course if you have a leaky house with little insulation, you're throwing money out the window/door, so the first consideration for a good ROI is better air sealing and insulation.

I think the comment was saying below 30F and below 10F. Much warmer than you're saying.

Also..

> It is warmer than -16C/3F at Chicago (O'Hare) for 99% of the time (i.e., except for 4 days a year), and warmer than -18.7C/-2F for 99.6% of the time (2 days).

If my heat doesn't work for those days, I'm kind of boned. Four days per year without a working heat pump? That's a mess.

At face value, then in the worst case that's just 4 days per year of using resistive heat to keep a home warm.

Which is, of course, very expensive to use -- but it's only expensive for those 4 days. Resistive heat can be avoided for the other 361.2425 days in a year.

In the US (as of August of 2025), the average price of residential electricity per delivered kWh is $0.1762 [1].

If using resistive heat averages 4kW during each of those 4 days (it's probably either more than that, or less than that, but ballparks are ballparks), then that's about $16.92 for each of those days. Or: $67.66, per year.

Not so bad, right? Or at least, not "boned."

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

> At face value, then in the worst case that's just 4 days per year of using resistive heat to keep a home warm.

The design philosophy for using 1% is that you may end up having to run your heating (or cooling) 24/7 to keep up with temperature delta between outside and desired inside, but it will keep up with the demand.

The rest of the time (99%) the mechanicals only run intermittently. Also note that the 1% would not necessarily occur every year: it is just the historical average. The charts also have the 0.4% extremes if you want to be extra conservative, but most building codes specify 1% because that is what experience has shown is a good trade-off.

Part of the process (in the US) is to use what is called the Manual J to determine/estimate/calculate how much energy is needed to maintain a particular temperature (typically ≥70F/21C in winter, ≤75F/24C in summer):

* https://www.acca.org/standards/technical-manuals/manual-j

* https://www.youtube.com/@HomePerformance/search?query=Manual...

> The Cooling Design Day is effectively the "worst case" day for your air conditioning loads. The "worst case" hour of this day determines equipment capacity, fan sizes, and subsequently duct sizes. This largely impacts first cost. The Design Hour also impacts peak KW demand which often has a huge impact on the utility bill.

* https://energy-models.com/blog/hvac-what-cooling-design-day

* https://hvac-blog.acca.org/sizing-selecting-hvac-equipment-p...

* https://www.airequipmentcompany.com/2021/what-does-design-da...

Here's an overview of the design process for one particular municipal jurisdiction:

* https://www.suffolkva.us/DocumentCenter/View/7362/Understand...

I understood all of that when I wrote my comment.

The choir's appreciation towards this unnecessary lesson is not very good.

So gas hash higher reliability and is cheap for the times you need heat the most, whereas heat pumps might not work and are not cheap at the times you need them the most?

I’ve had a gas furnace keep me and the water heated multiple times in a cold weather power outage.

How did you run the fans on your gas furnace without electric power?

If you have a backup generator, is it too small for your AC in the summer?

Gas generator. I think it would be too small for my air conditioner in the summer (5 ton).

I would never use the generator in the summer though, doesn’t get that hot in the Pacific Northwest.

> So gas hash higher reliability and is cheap for the times you need heat the most, whereas heat pumps might not work and are not cheap at the times you need them the most?

The major manufacturers have systems that will use the heat pump when the temperatures are not 'crazy', and kick in fossil at a certain point:

* https://www.trane.com/residential/en/resources/glossary/dual...

* https://www.carrier.com/residential/en/ca/homeowner-resource...

* https://www.lennox.com/residential/buyers-guide/guide-to-hva...

Depending on the cost of power and fossil fuels, you can program it to switch over once the COP becomes too low to justify running up kWh on your meter.

But whereas in the past heat pumps would have their COP drop around 40F/5C, modern systems can be fairly efficient at much lower temperature nowadays:

* https://neep.org/heating-electrification/ccashp-specificatio...

You have heat pumps running in Alaska:

* https://www.adn.com/business-economy/energy/2024/09/01/energ...

* https://alaskarenewableenergy.org/wp-content/uploads/2024/10...

That’s true, but still doesn’t always make heat pumps the most cost effective choice to operate. For example, last winter I paid an average of $0.24/kWh for electricity vs $0.05/kWh for natural gas. Even if a heat pump had a perfect 4.0 COP all winter, gas would be ~15% cheaper. Electricity prices really need to come down before it will be viable for everyone.

Yeah. Sadly the trend does not seem to be heading that direction what with the current admin’s … policies and the whole … AI … thing.

Get solar.

I’ve tried. For it to be at all viable on my property, I’d need to cut down a bunch of trees. I’d rather keep the trees and pay someone else with solar panels.

That makes sense. Is that legal?

I mean, in many countries, often either the government or a company closely allied to the government has been granted a legal monopoly on selling electrical energy, so buying electricity from other people is illegal.

Not to mention, lots of places have time of use electricity pricing which makes it even worse. This is the problem with running my heatpump when its cold, some of the coldest times (right before dawn) coincide with peak time-of-use prices

where do you live that the highest electricity prices are before dawn?

Does your 0.05/kWh include the distribution costs? The thing to do once you go to heating with gas is to just switch completely to electricity and turn off gas. In my experience (admittedly not in the US, but several other countries) distribution cost often more than double the $/kWh for natural gas (especially if you only heat part of the year).

This varies quite a bit based on location for instance here in Florida natural gas is $0.13/kWh while electricity is about $0.12/kWh, also where I live there is no piped NG so it would be propane delivered to a storage tank which is even more expensive.

Also the winters are mild here so basically everyone has either a heat pump or the further south you go it's just heat strips because heat is rarely used so not worth the cost.

So any kind of blanket statement about heat pumps vs gas heat would be folly, but due to improvements in cold weather heat pumps and solar power are allowing them to make much more sense in more places.

There are many advantages to decoupling fuel combustion from its energy use, burning NG at a power plant relatively efficiently with much better emission controls, then distributing on electric grid for use more than just heating, while allowing the home to heat from many different energy sources and allow for grid down backup as well.

https://www.eia.gov/dnav/ng/ng_pri_sum_a_EPG0_PRS_DMcf_m.htm

https://www.eia.gov/electricity/monthly/epm_table_grapher.ph...

They have good heat output down to very low temperatures, but not good efficiency.

The CoP is often around 2.0 at those very low temps, though (and of course the heat energy demanded is higher).

My heat pump, in Colorado, kept the house warm at -18°F last winter. Without firing up the backup resistance heating strip. I think it works.

(It is more expensive to operate than the natural-gas furnace was, though).

Insulation matters as well and I’m guessing your Colorado house is far newer and better sealed than most New England homes.

I don't know what sort of heat pump systems are common in the US, but Sweden (and AFAIK Norway and Finland as well), are probably >%80 heat pump for single family homes (most apartments are community heating at least in the larger cities). So it's absolutely now problem to run a heat pump even if it is very cold outside, but if you want to improve efficiency in areas that are super cold you can drill into the ground for a heat sink (those are called Bergvärme in Sweden).

Regarding cost, in most of the countries I've lived in a large fraction of the cost in the gas bill was the distribution cost. So once you switch to a heat pump, you also switch to electric cooking and even if heating with electricity would be significantly more expensive you would still win. Is that different in the US?

It varies significantly by locale. I've seen people post online about how it made little sense to keep just one gas appliance because of significant savings. I'm in Iowa, which typically heats on natural gas in urban areas. I have a natural gas central furnace and water heater. My clothes dryer is electric, and I have a 3 head heat pump which I use for comfort in a couple rooms. The house is an early 2000's standard builder-grade home.

For September, $12.31 of my $27.01 gas bill was variable based on my consumption.

In December, $84.82 out of my $99.65 total was consumption driven.

I've run numbers on whether it'd make financial sense to go electric for heating, and the break even point is in the 30-40 degree vicinity. With temperatures 20 and under a healthy chunk of the year, unfortunately the added expense doesn't make financial sense.

It works just fine during winters if you do it properly and couple them with ducts that are a couple of hundred meters deep.

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