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Hmm. The coefficient of a properly installed ground or water source heat pump can hit 4 or 5. Which means for each kw of power driving the contraption, up to 5k

Hmm. The coefficient of a properly installed ground or water source heat pump can hit 4 or 5. Which means for each kw of power driving the contraption, up to 5kw of heating or cooling comes out. They're not creating heat, but moving it from one place to another. Air source is rather less, not sure of the figures. There's no reason a heat pump can't heat a house and water as well as cooling it. Gas doesn't even run at 100% efficiency as some of that heat is disappearing out the flue. So unless gas is under a quarter of the price of electricity it should pay, and pay well...

lotsofpulp 7y ago
I found the source of confusion. I was under the assumption that a heat pump and electrical resistance heating were the same thing. But they are not, however, a heat pump is never used in actually cold places, because: >In most cases, an experienced HVAC technician will opt to install a furnace over a heat pump if they have access to natural gas. The exception to this is when a home is located in the coastal areas of California and the gulf states. >Because heat pumps are transferring heat from one area to another, what happens if it is -20 degrees outside in the middle of a North Dakota winter? Is there any heat to transfer into your house? That’s the catch. >A heat pump only works well if the temperature is above freezing, and is almost useless in the middle of a harsh northern winter. Ideally a heat pump is used when the temperature outside is over 40-50 degrees fahrenheit (and are VERY inefficient below 30-32 degrees), so heat pumps are out if you live in Montana unless you also have a supplemental means of heating your house. In fact, heat pumps are actually designed for coastal climates in the southern states. So what do people in Bozeman, Montana do? They use a furnace, or a wood-burning stove! https://asm-air.com/hvac/heat-pump-vs-furnace-pros-cons/ https://asm-air.com/hvac/heat-pump-vs-furnace-pros-cons/
- NeedMoreTea 7y ago
  That page is talking total crap. Must be trying to sell you a furnace! Heat pumps are pretty common in Scandinavia, and readily available in Canada and other cold places. I found this on a Canada gov website: "At –8.3°C, the COP is typically 2.3". So at 17°F in American money, that's 2.3kW out for every 1kW in, and air source is the least efficient type. https://www.nrcan.gc.ca/energy/publications/efficiency/heating-heat-pump/6831 https://www.nrcan.gc.ca/energy/publications/efficiency/heati... Heat pumps for heating do degrade in efficiency as temperature drops, but stay cost effective down to -15°C, or -20°C or so. Supposedly, newer ones go even lower still. With ground source you just dig a bit deeper, as assuming we're not talking permafrost it's fairly easy to reach efficient temperatures.
  - lotsofpulp 7y ago
    Huh, looks like I have more to learn. I’ve only ever seen gas furnaces used to heat wherever there is gas supply available in the US (Northeast/Midwest/Pacific Northwest). Heat pump is only used as air conditioner if gas available. I assumed this was because it’s not possible or efficient to operate a heat pump in colder temperatures.
    - NeedMoreTea 7y ago
      Mainly cost I'd say. 20 or 40 years ago, depending where you were, gas was cheap enough that it mostly wasn't worth caring that much, and electric anything was the expensive option. Aircon for cooling was a much easier choice. These days it's starting to look hugely attractive both ways, and I think will be ever more so. Cold areas usually have a mostly unused backup heater in heat pumps, for those few times record breaking cold arrives, and of course the nearer you get to a COP of 1 (1kW in = 1kW out) the longer it takes to pay back the extra cost.

lotsofpulp 7y ago

I found the source of confusion. I was under the assumption that a heat pump and electrical resistance heating were the same thing. But they are not, however, a heat pump is never used in actually cold places, because: >In most cases, an experienced HVAC technician will opt to install a furnace over a heat pump if they have access to natural gas. The exception to this is when a home is located in the coastal areas of California and the gulf states. >Because heat pumps are transferring heat from one area to another, what happens if it is -20 degrees outside in the middle of a North Dakota winter? Is there any heat to transfer into your house? That’s the catch. >A heat pump only works well if the temperature is above freezing, and is almost useless in the middle of a harsh northern winter. Ideally a heat pump is used when the temperature outside is over 40-50 degrees fahrenheit (and are VERY inefficient below 30-32 degrees), so heat pumps are out if you live in Montana unless you also have a supplemental means of heating your house. In fact, heat pumps are actually designed for coastal climates in the southern states. So what do people in Bozeman, Montana do? They use a furnace, or a wood-burning stove! https://asm-air.com/hvac/heat-pump-vs-furnace-pros-cons/ https://asm-air.com/hvac/heat-pump-vs-furnace-pros-cons/

NeedMoreTea 7y ago
That page is talking total crap. Must be trying to sell you a furnace! Heat pumps are pretty common in Scandinavia, and readily available in Canada and other cold places. I found this on a Canada gov website: "At –8.3°C, the COP is typically 2.3". So at 17°F in American money, that's 2.3kW out for every 1kW in, and air source is the least efficient type. https://www.nrcan.gc.ca/energy/publications/efficiency/heating-heat-pump/6831 https://www.nrcan.gc.ca/energy/publications/efficiency/heati... Heat pumps for heating do degrade in efficiency as temperature drops, but stay cost effective down to -15°C, or -20°C or so. Supposedly, newer ones go even lower still. With ground source you just dig a bit deeper, as assuming we're not talking permafrost it's fairly easy to reach efficient temperatures.
- lotsofpulp 7y ago
  Huh, looks like I have more to learn. I’ve only ever seen gas furnaces used to heat wherever there is gas supply available in the US (Northeast/Midwest/Pacific Northwest). Heat pump is only used as air conditioner if gas available. I assumed this was because it’s not possible or efficient to operate a heat pump in colder temperatures.
  - NeedMoreTea 7y ago
    Mainly cost I'd say. 20 or 40 years ago, depending where you were, gas was cheap enough that it mostly wasn't worth caring that much, and electric anything was the expensive option. Aircon for cooling was a much easier choice. These days it's starting to look hugely attractive both ways, and I think will be ever more so. Cold areas usually have a mostly unused backup heater in heat pumps, for those few times record breaking cold arrives, and of course the nearer you get to a COP of 1 (1kW in = 1kW out) the longer it takes to pay back the extra cost.