Oh... you said "PV" in both sentences, which is specifically converting light to electricity; that's what threw me. For heating a house with solar (not PV) --

Oh... you said "PV" in both sentences, which is specifically converting light to electricity; that's what threw me. For heating a house with solar (not PV) -- it would depend on insulation level, I'd imagine. I do know people who use it for "most of the time" water heating, with good results.