I think with multiple houses, yur gunna have to go with wells.   Our bank built new about 3 years ago, they put around 30 wells for their geo requirements.

My December heating bill was 40 bucks, Jan, and Feb have both been around 120.........not sure whats up, but looking forward to this next months, weve averaged about 30 degrees warmer, even though its still too cold for end of March............(like to get the wheat it)

Good luck