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I understand the principle of heat pumps, and it makes sense that a heat pump / AC split system is more efficient then for example resistive heating for heating a house. In this case, the heat pump moves heat between inside and outside the conditioned space.

But all the heat pump water heaters I have seen are a packaged unit, with the evaporator coils just above the water heater tank. Since water heaters are normally installed inside the conditioned space, this setup just pumps heat that has been heated by the furnace or whatever else heats the home, and pumps it into the water. So it's not like you are using the "free" heat from outside, you are just using your normal house heat source to heat the water in a roundabout way. Obviously, during AC season, this would be an advantage. But am I seeing this right that the advantage is rather minimal during heating season, or am I overlooking something?

PhilippNagel
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  • Relative cost of fuel, unless the house is heated with electric resistance. There are (a few, even more expensive) split units that heat from outside air, and some of the packaged units claim to work with ducted outside air in non-freezing climates. In a "primarily A/C climate" they would still be a win, I think. Personally, I punted since none of the options look great for my application (cold climate) yet. Eventually I'll supplement with (a clean-burning) wood boiler. – Ecnerwal Mar 22 '21 at 14:29
  • basements get heat from the ground in the winter; I saw people in texas camping in basements as they were the warmest place in the power-less house. – dandavis Mar 23 '21 at 19:30

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