alt Hacker NewsThere's a pretty significant upfront cost in getting them drilled, and many homes need the vertical drilling if they don't have sufficient yard space for a horizontal system. It gets harder if you have your own septic drain field too, as that will complete for yard space.
The cost difference is pretty massive- 3-10x for a vertical system. If you live in a city or a suburb with tiny lots, that's your only option though.
Nat gas and central AC are way cheaper.
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Although if you needed a new septic field, I would think ground source thermal would be significantly deeper than a drain field which is only like a foot or so down so you could stack them.
Air source heat pumps are insanely more efficient and just plain better these days too. It used to be that if the air was below 40F you couldn't heat your house with a heat pump. Now, you can heat your house even when it's -10F
I paid about EUR 4500 for a 114 meter drill hole including installation of brine (ethanol in my case actually) and removal of spoils. My 8kW heat+water pump was about EUR 7000.
I can spec out a gas burner for about EUR 4000 and a central AC for EUR 5000, but I bet the efficiency of the ground source heater would quickly trump the cost of buying gas regularly.