i have a geothermal system in my house so i know a bit about how they work. the ground temperature of whereever you live at about 8 to 10 feet down will be aproximately equal to the average yearly temperature at your location. for example the ground temp here in south central wisconsin is about 55 degrees. the geo unit at my house extracts heat from the ground all winter, at about the 300 to 400 percent efficiency that was stated in the earlier post, and dumps heat into the ground in the summer when we need the ac. i cant remember what the seer rating of my unit is when doing ac but it was about 4 times higher than the new efficient unit i had installed on my last house. the only disadvantage to the units is they need to be put down deep and that horizontal placement needs alot of room. the trench for my exchange tubing was 10 feet deep and near 300 feet long.