Drilling is about half the cost. It's fairly cost efficient if they do it when building the house, much less so otherwise. It's basically "free" if your house

Drilling is about half the cost. It's fairly cost efficient if they do it when building the house, much less so otherwise. It's basically "free" if your house needs a well anyway. (this assumes a lot about the ground under your house but it's relatively true ;P) If you live in a mild climate, you are just not going see a lot of payback because as you said, you don't spend a lot. Note: Most of them also provide hot water, not just heating and cooling But all told, the path to making it popular would be to make it part of new construction. I understand why they want to try to make retrofitting cheap, but it's just not even close right now.