I looked into a geothermal unit, gave that idea up for a wood stove.
Geothermal is an expensive option, and works best in slightly cooling dominated climates, not heating dominated ones. First, they're expensive. To be practical they need to save you money in winter and summer so you get double duty return on your investment to cover their initial costs. The reason they do better in cooling dominated climates is that as they cool your house you get more returns as the heat generated from cooling can be used to heat your domestic hot water so it performs double-duty in cooling mode. Whereas heating mode the cold created isn't used for anything so you get more return running in cooling mode than heating. In the north our ratio is like, 6000-8000 heating degree days and 400-600 cooling. In summer, it would hardly be used for cooling your house much in the north, which means in summer you need another source for domestic hot water. It also means you will only get less than half the payback of someone in the south. The next reason is soil temperature. If it's 30 outside and you live in the south your soil temperature is probably 60. A little more efficient for the geothermal to transfer that heat into the living area. Whereas, in the North you soil temperature may be 50. Not as efficient pulling the heat out of the 50 degree earth. Up north that makes it great for cooling, however you don't cool very often up north. It is more efficient than an air heat pump but also more expensive. Geothermal uses a decent supply of electricity which hinders payback time since electricity is expensive (but not as much as an ac unit or electric heat).
I did a payback of a geothermal unit, I live in the north. Cost for installation, convert my house over to HVAC, drill 9 holes into the ground, installation was estimated to be $24,000 IF they didn't hit rock which I live on rock. Doing a heating degree cost analyses vs. cooling my estimated savings/payback going to geothermal was 211 years! I then looked into Solar, which is the best form of heating, but like geothermal not cheap. Sure, the solar panels are cheap and use little electricity, but you need to have a new roof, radiant floor heating, new efficient windows, well insulated attic, floors, and should have insulating window shades so although a solar heating system is cheap the other stuff that you have to do for it to be feasible is not. But, at least with solar those things are things you should do anyway and I'm about 65% there to being able to heat with solar.
So, if you live in the north I wouldn't consider geothermal. Maybe put in another wood stove, think about solar, put in radiant floor heating, the do-it-yourself strap up kind, maybe consider a solar hot water heater which doesn't require all the things to your house solar heating does. If you live in the warmer middle-states, or south, then geothermal may be practical. Last month I saw someone on the web building a house in Canada very excited about the Geothermal heating system they decided to have installed in it, I felt bad for the couple, it's not going to work like they think it will, of all places Canada.