So I am looking into replacing existing forced air heating system in an old 2500 sq. ft. house. I want to put in cooling (either by replacing entire HVAC or by adding on cooling to existing system with additional returns). Since gas is not going to get any cheaper and electricity is not going down any time soon, I am thinking about possible alternatives. I live in Boston area. I have been looking into geothermal information, but I am not finding any average system costs out there. I have enough of a back yard to put in vertical closed loop system.