Geothermal heat pumps use the constant temperature of the earth as the exchange medium instead of the outside air temperature. A few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F to 75°F. This ground temperature is warmer than the air above it during the winter and cooler than the air above it in the summer. A geothermal heat pump takes advantage of this constant temperature by exchanging heat with the earth through a ground heat exchanger.