Here's my train of thought on what you are doing.
A geothermal unit (or even an air to air heat pump) would heat your house for considerabally less than your propane. A geothermal would probabally make your electric bill go up by 100-150 per month, wich is about 600-1000 per heating season. At an inital cost of only about 5k more than the boiler. and if you still wanted to cut the wood each winter, 8-9cords a winter would easily sell for enough to heat your house for the entire winter. And without having to ever worry about about fixing a fire again. But if you want to heat another building that would be another issue.