So, your electric bill is lower, but if it is collecting that much heat in your basement enough to overcome its balance point on a consistent enough run rate to save ‘big bucks’, where is the heat energy coming from that gets to the basement for it to extract when it’s 30 degrees outside?

Your floors are providing the heat via your furnace heating the house. If you read my post I’m not giving hard numbers or saying they don’t have a use case, but the movement of heat energy is very complicated, so much so my work is done for the Department of Energy, ASHREA and ACCA and is only accepted when it’s corroborated with three other engineers work. If your loosing that much heat energy from the buildings thermal envelope, your biggest savings are insulating your house, in which case once you would, your heat pump water heater that has a high balance point of close to 50° would end up running almost entirely on its electric element.