To everyone saying this is impossible. This is proven tech and it's actually not uncommon to heat your house like this already today. Depth of a hole in your backyard is around 100-200m and one such hole provides more than enough for one big house.

Payoff for such investment to break even with more basic forms of heating is around 5-10 years in cold northern europe climates. Sadly most people have shorter foresight than that when it comes to economic planning.