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Heat pumps based on air do not work economically below 40F. Neighbor has one and his electric bill is out of control in the winter. Drop below freezing and th

Heat pumps based on air do not work economically below 40F. Neighbor has one and his electric bill is out of control in the winter. Drop below freezing and the system will pump heat out of the house to de-ice the external unit, and electric resistance heat will kick in. We have dual fuel, so we burn oil below 40F. Works great. If you can afford it, putting in a heat pump that works off of ground will eventually pay for itself.

vvanders 8y ago
How new is the heat-pump? We put one in our house this year and been in the 20-40F range for the last 2 months. So far we haven't seen resistive heating kick in more than when it's above 40F.
Robotbeat 8y ago
Doesn't work below 40F? That's just not true unless you're using a very poor, cheap heat pump. Modern, high efficiency air source heat pumps can work well even below 0F.
willvarfar 8y ago
Outside temperature definitely affects an air heat-pump's performance, but the ones common in sweden stop being effective at -10c or even -15c. I have a ground-source pump and its brilliant. But plenty of my neighbours are happy enough with air-source pumps.
- bklyn11201 8y ago
  Recent conversations with net-zero builders indicate that ground-source pumps are being pushed away for most single-family residential projects in favor of the new-generation, highly-effective, cold-climate air-source heat pumps. Mitsubishi and Fujitsu seem to have a large lead in cold-climate air-source heat pumps that are rated effective to -13F (anecdotal reports greenbuildingadvisor.com indicating effectiveness down to -20F). Yet, talking to builders, contractors, friends, and family, you will often still hear old tales about how "heat pumps aren't effective below 40F". Heat pumps come in a wide range of flavors. It's clearly possible to heat your house exclusively using an air-source heat pump in most USA climates.
  - fastbeef 8y ago
    There's a huge difference between air-source heat pumps and rebranded AC units running in reverse. We have a Mitsubishi FH35 6kw heat pump that easily heats 80 m2 (800 sq feet) down to -13 C this winter.
    - toomuchtodo 8y ago
      Do you recommend the model you quoted in your comment?
      - fastbeef 8y ago
        I do, it's fantastic! Just make sure to get a good installer for it.
        jjtheblunt 8y ago
        As a fellow northern climate person, now in Arizona, have you any idea its efficacy in the 45 celsius normal summer heat, for cooling?
alekq 8y ago
They do work, but with decreased efficency, which in the end line has an effect on total power output (not enough to satisfy heating capacity/needs of user’s installation) and increased energy consumption. Most of modern heat pumps (air to water) can work without issue all they way to -15/20* C.
- jhallenworld 8y ago
  Yeah, they have two-stage pumps for cold weather. I thought about it when I upgraded my heat: gas furnace and electric heat pump had about the same running cost, but heat pump was much more expensive to install and much less reliable / more expensive to service.
aoner 8y ago
Modern heat pumps are still highly efficient at 40F (4C) the coefficient of performance is 4+ at this temperature. We switched from an hybrid set to a full-electric setup (also PV and solar thermal) and are super happy with (live in Amsterdam, so regularly goes below 40F/4C). There's probably something wrong with your neighbors setup. I'd say practical limits of current models are probably around -20C (-4F) If you're interested here is an example datasheet[1] of an air to water heat pump (2018) (using Celsius here): Mitsubishi PUHZ-SHW112YAA Guaranteed operating range (outdoor): Heating: -28 to +21 Domestic hot water: -28 to +35 On page 108 you can find the actual co-efficient of performance (COP) for different outside temperatures and inside water heating temperatures. As an example: at -10 and an water temperature for heating at 25 you still get a COP of 3+. That means that 100% electricity moves 300% of heat into your house. [1]: https://www.mitsubishi-les.info/database/servicemanual/files/201803_ATW_DATABOOK.pdf https://www.mitsubishi-les.info/database/servicemanual/files...

vvanders 8y ago

How new is the heat-pump? We put one in our house this year and been in the 20-40F range for the last 2 months. So far we haven't seen resistive heating kick in more than when it's above 40F.

Robotbeat 8y ago

Doesn't work below 40F? That's just not true unless you're using a very poor, cheap heat pump. Modern, high efficiency air source heat pumps can work well even below 0F.

willvarfar 8y ago

Outside temperature definitely affects an air heat-pump's performance, but the ones common in sweden stop being effective at -10c or even -15c. I have a ground-source pump and its brilliant. But plenty of my neighbours are happy enough with air-source pumps.

bklyn11201 8y ago
Recent conversations with net-zero builders indicate that ground-source pumps are being pushed away for most single-family residential projects in favor of the new-generation, highly-effective, cold-climate air-source heat pumps. Mitsubishi and Fujitsu seem to have a large lead in cold-climate air-source heat pumps that are rated effective to -13F (anecdotal reports greenbuildingadvisor.com indicating effectiveness down to -20F). Yet, talking to builders, contractors, friends, and family, you will often still hear old tales about how "heat pumps aren't effective below 40F". Heat pumps come in a wide range of flavors. It's clearly possible to heat your house exclusively using an air-source heat pump in most USA climates.
- fastbeef 8y ago
  There's a huge difference between air-source heat pumps and rebranded AC units running in reverse. We have a Mitsubishi FH35 6kw heat pump that easily heats 80 m2 (800 sq feet) down to -13 C this winter.
  - toomuchtodo 8y ago
    Do you recommend the model you quoted in your comment?
    - fastbeef 8y ago
      I do, it's fantastic! Just make sure to get a good installer for it.
      - jjtheblunt 8y ago
        As a fellow northern climate person, now in Arizona, have you any idea its efficacy in the 45 celsius normal summer heat, for cooling?

alekq 8y ago

They do work, but with decreased efficency, which in the end line has an effect on total power output (not enough to satisfy heating capacity/needs of user’s installation) and increased energy consumption. Most of modern heat pumps (air to water) can work without issue all they way to -15/20* C.

jhallenworld 8y ago
Yeah, they have two-stage pumps for cold weather. I thought about it when I upgraded my heat: gas furnace and electric heat pump had about the same running cost, but heat pump was much more expensive to install and much less reliable / more expensive to service.

aoner 8y ago

Modern heat pumps are still highly efficient at 40F (4C) the coefficient of performance is 4+ at this temperature. We switched from an hybrid set to a full-electric setup (also PV and solar thermal) and are super happy with (live in Amsterdam, so regularly goes below 40F/4C). There's probably something wrong with your neighbors setup. I'd say practical limits of current models are probably around -20C (-4F) If you're interested here is an example datasheet[1] of an air to water heat pump (2018) (using Celsius here): Mitsubishi PUHZ-SHW112YAA Guaranteed operating range (outdoor): Heating: -28 to +21 Domestic hot water: -28 to +35 On page 108 you can find the actual co-efficient of performance (COP) for different outside temperatures and inside water heating temperatures. As an example: at -10 and an water temperature for heating at 25 you still get a COP of 3+. That means that 100% electricity moves 300% of heat into your house. [1]: https://www.mitsubishi-les.info/database/servicemanual/files/201803_ATW_DATABOOK.pdf https://www.mitsubishi-les.info/database/servicemanual/files...