Sure, but the max frost-line even in Anchorage, Alaska is like 10-feet down. A 5-foot deep hole is gonna get you temperatures that a heat pump can function at

Sure, but the max frost-line even in Anchorage, Alaska is like 10-feet down. A 5-foot deep hole is gonna get you temperatures that a heat pump can function at 365 days a year in all of the continental United States, and most of Canada and Northern Europe.