Looking at building a shop in New York, and had planned all along to put in floor heat in it.  I can get propane, fuel oil, wood, or coal, so no real problem in getting a heat source.  Then last week I saw a video about using geothermal tubes to keep a greenhouse at a minimum of 52 in Nebraska, and it got me thinking about using geothermal to heat the shop.  If everything, including the floor is well insulated, could it keep a shop at 50 or so, with a furnace of some kind to add a little heat?  My memory is that 50 isn't bad in the winter, but that was twenty years ago, and maybe I'm a little hazy.  For what it's worth, I can do the install myself, so the main cost will be materials and machine time.