I checked into it, and it seems like a good deal, even here in PA. I'm no engineer but the concept seems pretty simple.
Liquid stored/circulated under the ground is always around 55 degrees. That 55 degree liquid goes through some type of compressor that bumps the temperature up even further, using properties of liquid that gets compressed/decompressed. This heated liquid is then run through a heat exchanger which warms the air that is deleivered into your home. If gets really cold, a backup heat source is used to help out.
The savings come in because of the difference. Lets say its 20 degrees out, and you like your thermostat set at 70. Your furnace has to constantly try to warm the 20 degree air to 70 degrees. But with the geothermal system, your getting 65 degree air at minimal cost, so the heating system only has to heat the air 5 degrees.
I've seen comparison charts where geothermal can save up to 75% over natural gas and electric, and 90% over propane.
Check around for different contractors. I talked with a couple of guys that quoted prices close to yours, then I found a guy with good references that charges around $12k. Does all the work himself except for the drilling, which he has a friend do. And he will just tie it into my existing system, so I already have the auxiliary heating system, and can always go back to it 100% if need be. With gas prices going up, I'm seriously considering it, because with what I'm spending now, vs what I will save, the system will pay for itself in less than 7 years, even faster if natural gas prices continue to rise. The only thing stopping me, is that we have talked about building a place, so we wouldnt be here long enough to get our money back. But if we build a place, I will definitely have it there.
I am like you, with an old house. Its a big old Victorian, built over 100 years ago, and is very drafty. If you havent done it already, get good windows, and attic insulation. I had new windows put in a couple of years ago, and had insulation blown into the attic floor, and my heating bills dropped by 60%. I got my money back in 2 years, which really surprised me. BTW, good windows dont have to cost an arm and a leg. I got mine through a place called Window World, which advertises full featured vinyl-clad windows (with screens) at $249 each, installed. I added the solar and gas options, and they were still only $300 each installed.
