3 ms·

It depends on your definition of efficiency. Electric heat is considered 100% efficient as 100% of the watt hours that go into the device eventually get turned

It depends on your definition of efficiency. Electric heat is considered 100% efficient as 100% of the watt hours that go into the device eventually get turned into the same amount of heat. A heat pump moves heat from outdoors to indoors. The outdoor heat lost is ignored in the efficiency calculation (as it should be), and thus the efficiency question is how many watt hours of electricity does it take to move a watt hour of heat (joules) from outside to inside. Depending on the temperatures involved, it's usually a multiple, for example, 1 wH of electricity moves 4 wH equivalent of heat indoors, ie: 400% efficient. If you consider the whole system, much of the electricity for a heat pump may come from burning natural gas elsewhere, which involves losses along the way. This is still usually better than 100% overall efficiency. Direct natural gas heating is less than 100% efficient too. Most furnace systems are about 20% loss in exhaust, though they can be much better. This is still usually better than burning the gas at a plant, converting to electricity and then heating with resistive electrical in your home.

syshum 5y ago
Most modern gas furnaces are 95% AFUE, the minimum in northern US states is 90% And comparing AFUE efficiency to HSPF is not really a thing, you can not look at a gas furance that is 95% AFUE, and a Heat Pump that is "400%" claim that the gas furnace is must less "efficient" that is not how any of those works. To be clear a heat pump at temps above 25 degrees Fahrenheit is more efficient but comparing the metrics in this manner is a bit misleading Further heat pumps are good to 25 to 30 degrees Fahrenheit, under that a gas furnace is normally used to supplement a heat pump in colder climates. Most heat pump manufacturers do not recommend operating a heat pump in below freezing conditions
- dieortin 5y ago
  Then how would you say it should be compared?
- rudedogg 5y ago
  > Further heat pumps are good to 25 to 30 degrees Fahrenheit, under that a gas furnace is normally used to supplement a heat pump in colder climates. Most heat pump manufacturers do not recommend operating a heat pump in below freezing conditions Just wanted to chime in that they do make a lot of low-temp heat pumps, going down to -30f now. The efficiency drops dramatically at temps that low, the best site to look at cold-weather models is https://ashp.neep.org/#!/product_list/ https://ashp.neep.org/#!/product_list/ If you look though, the "COP @ 5 degrees F" for a lot of models is above 2.0, which from my understanding means you'll be using 1/2 the electricity someone with baseboard (resistance) heat would. And above those temps the COP gets much higher.

syshum 5y ago

Most modern gas furnaces are 95% AFUE, the minimum in northern US states is 90% And comparing AFUE efficiency to HSPF is not really a thing, you can not look at a gas furance that is 95% AFUE, and a Heat Pump that is "400%" claim that the gas furnace is must less "efficient" that is not how any of those works. To be clear a heat pump at temps above 25 degrees Fahrenheit is more efficient but comparing the metrics in this manner is a bit misleading Further heat pumps are good to 25 to 30 degrees Fahrenheit, under that a gas furnace is normally used to supplement a heat pump in colder climates. Most heat pump manufacturers do not recommend operating a heat pump in below freezing conditions

dieortin 5y ago
Then how would you say it should be compared?
rudedogg 5y ago
> Further heat pumps are good to 25 to 30 degrees Fahrenheit, under that a gas furnace is normally used to supplement a heat pump in colder climates. Most heat pump manufacturers do not recommend operating a heat pump in below freezing conditions Just wanted to chime in that they do make a lot of low-temp heat pumps, going down to -30f now. The efficiency drops dramatically at temps that low, the best site to look at cold-weather models is https://ashp.neep.org/#!/product_list/ https://ashp.neep.org/#!/product_list/ If you look though, the "COP @ 5 degrees F" for a lot of models is above 2.0, which from my understanding means you'll be using 1/2 the electricity someone with baseboard (resistance) heat would. And above those temps the COP gets much higher.