And never mind ground-source heat pumps [1] (although I know the topic was specifically solar).

[1] https://en.wikipedia.org/wiki/Ground_source_heat_pump

You don't even need to go that far, put 100m of tubing 2m underground and plug it in your heat recovery ventilation system, bam free winter freeze protection/pre warming and free summer cooling, all you need is a 30w pumps and you will save hundreds of kw per year

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a_random_name 4 hours ago | parent [-]

uh no... You still need a heat pump. The water coming from that system would be like 50 degrees, far too cold for heating.

	▲	benlivengood 10 minutes ago \| parent \| next [-]
		Heat recovery ventilation systems exchange inside air for outside air through an air to air heat exchanger (modern energy-efficient houses are built too tight for natural air exchange). If you make the incoming outdoor air an even 50°F (except when the outdoor temperature is between about 50° and 70°) then you spend less on heating and cooling.
	▲	toasty228 4 hours ago \| parent \| prev [-]
		I think my comment is pretty clear about the use case, this is obviously not water for your floor heating. You shouldn't even have that in a properly insulated house, way too much inertia. There are electric floor heating graphene foils that put out 20w per sqm, they're more than enough, no moving part, no maintenance, no bs, not even 20% of the price of a hydro floor heating, you can even install them yourself