7 ms·

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 -

by Tor3 4y ago

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.

HPsquared 4y ago
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)
- iso1631 4y ago
  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.
  - Jochim 4y ago
    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.
    - monkeynotes 4y ago
      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.
      - Jochim 4y ago
        > 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_source_heat_pump.jpg https://solarthermuk.co.uk/wp-content/uploads/2020/12/air_so...
- Tor3 4y ago
  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.
  - bitexploder 4y ago
    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.
- jghn 4y ago
  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.
  - space_fountain 4y ago
    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
    - jghn 4y ago
      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.
buran77 4y ago
> 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.
- Tor3 4y ago
  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.
  - buran77 4y ago
    > 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.
    - Tor3 4y ago
      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).
ajross 4y ago
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.
- xenadu02 4y ago
  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.
- philips 4y ago
  What heat pump model did you install?
- ericpauley 4y ago
  This is just a matter of pump size. People in colder climates size their pumps larger in expectation of these cold temperatures.
  - ajross 4y ago
    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.
    - shkkmo 4y ago
      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.
iamthepieman 4y ago
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+.
- monkeynotes 4y ago
  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.
  - fnbr 4y ago
    Were you able to install it with your existing furnace or did you have to replace the furnace?
    - zucked 4y ago
      They mention mini splits, which could very well be installed in addition to or even in lieu of a traditional central HVAC.
- EricE 4y ago
  Ductless mini splits are perfect for your use case.
User23 4y ago
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.
- flakeoil 4y ago
  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.
- PragmaticPulp 4y ago
  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.
  - monkeynotes 4y ago
    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.
- monkeynotes 4y ago
  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.
- chongli 4y ago
  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.
rawgabbit 4y ago
Who makes your heat pump? Want to know for my future potential purchase.
- bitexploder 4y ago
  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.
  - rawgabbit 4y ago
    Thank you.
- Tor3 4y ago
  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.
  - rawgabbit 4y ago
    Thank you.
yencabulator 4y ago
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)

by Tor3 4y ago

HPsquared 4y ago

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)

iso1631 4y ago
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.
- Jochim 4y ago
  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.
  - monkeynotes 4y ago
    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.
    - Jochim 4y ago
      > 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_source_heat_pump.jpg https://solarthermuk.co.uk/wp-content/uploads/2020/12/air_so...
Tor3 4y ago
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.
- bitexploder 4y ago
  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.
jghn 4y ago
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.
- space_fountain 4y ago
  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
  - jghn 4y ago
    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.

buran77 4y ago

> 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.

Tor3 4y ago
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.
- buran77 4y ago
  > 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.
  - Tor3 4y ago
    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).

ajross 4y ago

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.

xenadu02 4y ago
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.
philips 4y ago
What heat pump model did you install?
ericpauley 4y ago
This is just a matter of pump size. People in colder climates size their pumps larger in expectation of these cold temperatures.
- ajross 4y ago
  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.
  - shkkmo 4y ago
    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.

iamthepieman 4y ago

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+.

monkeynotes 4y ago
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.
- fnbr 4y ago
  Were you able to install it with your existing furnace or did you have to replace the furnace?
  - zucked 4y ago
    They mention mini splits, which could very well be installed in addition to or even in lieu of a traditional central HVAC.
EricE 4y ago
Ductless mini splits are perfect for your use case.

User23 4y ago

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.

flakeoil 4y ago
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.
PragmaticPulp 4y ago
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.
- monkeynotes 4y ago
  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.
monkeynotes 4y ago
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.
chongli 4y ago
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.

rawgabbit 4y ago

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

bitexploder 4y ago
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.
- rawgabbit 4y ago
  Thank you.
Tor3 4y ago
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.
- rawgabbit 4y ago
  Thank you.

yencabulator 4y ago

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)