I installed six geothermal loops to assist w/ floor heating back in 2000 on a 5/1. This was not an actual geo system w/ a compressor. I was pre-heating the floors to 50, then the gas heater would take over. In the evening, the heater would shut off, and I would simply run the circulator over night to maintain 50 . I was saving about about $300/month. But as the Winters have become milder, I found I am only running floor heat about 20-24 days per year. So in 05, I installed a geothermal heat pump and used the loops for that. That gets used about 9 months out of the year for heating/ cooling, and it has been a great use for the loop field. A true geo for floor heat will be expensive, and probably does not make sense for the amount of time floor heat is typically used.