My first thought on Geothermal.....head for the hills. Unless you have a huge place, and live in a climate that does not routinly get down to butt a$$ cold, you will never recoup the cost. The installs I've done are 25k and up. And, depening if you go with a trench or well syetem, your yard is gonna get jacked up in the process, so there is the added expense of repairing it. Then, you have reapirs......A geothermal sysem is not like any other HVAC system......not to many cheap fixes. When it breaks down, it;s gonna cost ya! a typical system is designed to last 15 years. So, lets put you on the low end at 25k for initial. In that 15 years add a couple three service calls, at god knows how much. Then, 15 years later.....time for new equiptment. another 10-15k. sure, it is a good idea, and green, But until the price comes way down, it is just not worth it.
My advice, heat pump. In the last few years, they have come a LONG way. They will extract heat from the outside air down to 15* before the back up comes on. Get a ahold of a Bryant dealer in your area. These tihngs are great! By far, the best I have installed. They now have variable speed drive blower motors. The thermomstat senses the temp difference in the house, cmpared to what it is set at, and will ramp the blower speed up and down a wide range, to efficently heat the home. They are amazing if you have a two story, especially for cooling. When you back up heat does kick on, below 15*, the furnace is very efficent. Close to 98%. Basically, that means for every one dollar you spend on propane, you are getting 98 cents worth of heat, and only losing 2 cents out the flu pipe.
I did a job for a guy that had 3 90% furnaces in his house. We took all 3 out and replaced them with the heat pumps. His gas bill was over 900$ a month. We took it down to a little under 200$, and raised his electric bill only 90$. Tell me that is not saving! You can expect to pay around 7k for a good system. But campared to a regular furnace and a/c at 5k, you will easily get your money back.