Geothermal heat pumps (sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat pumps) have been in use since the late 1940s. The application of geothermal heating/cooling has been named the most energy-efficient and environmentally sensitive of all space conditioning systems, by the Environmental Protection Agency. The system's basic concept takes advantage of the earth's constant temperature and can save homeowners 40 to 70 percent in heating costs and 30 to 50 percent in cooling costs compared to conventional systems. You can also realize a 30% tax credit from the federal stimulus program. The shallow ground, the upper 10 feet of the Earth, maintains a nearly constant temperature between 50? and 60?F (10?-16?C). Like a cave, this ground temperature is warmer than the air above it in the winter and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to heat and cool buildings.