I currently have a heat pump which is approximately 7 years old. Although it works well, I am considering replacing it when the time comes with a geothermal type pump. Anyone have any experience with these units? Is the installation cost prohibitive over regular heat pump equipment? Is there substantial savings by changing to this system? I understand that there is some federal money available for changing to these systems, but is that enough to make it worth it with the new higher SEER ratings of modern equipment?