Hi again - I've been doing research on 'ground tubes'. (Quick explanation...this is based on the principle that the soil underground remains at a pretty constant temperature throughout the year. So long tubes are installed and air is drawn through the tubes into the house (or furnace/AC area). So - as air is pulled through - the ground naturally heats/cools it closer to the ground temperature. Here in Upstate SC, the ground temperature is (supposedly) 61 degree Fahrenheit. So in the summer, I might pull in air when it's 90 degrees outside and the air will be cooled as it moves through the tubes. In the winter, the 40 degree outside air would be heated as it moves through the ground. Obviously, a lot depends on length/size of tube, etc. etc.) As I said, I've done research on this and am planning on trying it at my house. But has anyone here had actual experience with it and - if so - what did you think??