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)

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.

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...

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.

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.

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.

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...

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".)

What heat pump model did you install?

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.

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.

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.

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)