So we get nearly free air conditioning in the summer and supplementary heating in the winter? Of course we would be causing temperature changes and fluctuations below this frost line. What physical changes happen to objects or substances with heating and cooling? How about expansion and contraction? And what about vegetation that plants roots deep down into these areas we'd be monkeying around in? Will they tolerate theses changes? I also would have to think it take a more efficient heat exchanging system than just plastic pipe....which is actually more of an insulator. It would take metals or maybe some ceramics. This will surely drive up the cost and I don't think a 30 dollar bathroom fan that might help remove offensive odors in a bathroom is going to do much to bring heat into a house from a subterranean plumbing network.