I really wanted to install one when I built my house @ 7years ago. Since, I am not planning on moving anywhere the higher initial cost vs payback was not an issue. The problem I ran into was with the township rocket scientists. I wanted to install an open loop or pump and dump system. The extraction well would have been a rather shallow well 30-40 feet would have been plenty deep enough as I am 75 feet from the local ground water discharge point....resting atop a weathered schist that can really make some water. I was wanting to discharge into the local groundwater discharge point (stream) and was willing to install the discharge line as if a drunken sailor installed it from the house to the stream. This was to help alleviate any "perceived" thermal discharge issues into the stream. That however, was not the stroke of true ignorance that killed it. Nope...the morons insisted that I re-inject my discharge water back into the formation from where it came. Now I understand in certain parts of the country and in certain conditions...this is the best option for an open loop system....but hello I'm 75 feet from where it is headed???? After several attempts at educating the twp rocket scientists, stopping just short of producing a MODFLOW groundwater model, out of frustration and timing issues I bagged it. Ended up with a traditional heat pump with a propane back up unit.
Good luck and hopefully thing have progressed in the last 7 years. Also, you won't have to go through this execise with a closed loop system.....they seem to like those better.