[KMag]

My dad had a heat exchange loop buried in his back yard. I believe he had it buried below the frost line.

In any case, unless you're building on permafrost, you can bury your heat exchanger deep enough to have your heat source at least 0 C in the dead of Winter. Though, for most of the US, the time to recoup the extra cost of the heat exchange loop is pretty high/never (counting the time value of money).

[voisin]

I think there’s a bit more to this where you need to ensure the ground makeup can handle the exchange so that it is effective. My previous discussion was all about air heat pumps rather than ground based. As I understand it, air is around 1/3 - 1/4 the price and today’s technology is more efficient, but I am not an expert.