During the winter months fluid dissipates cool from the house to the ground, then before returning to the home the fluid is warmed by relatively constant ground temperatures. Even when the temperatures dip below freezing, a heat pump can extract heat from the ground and use it to warm your home. The warmth from the fluid is converted to hot air by circulating it through water-to-refrigerant and refrigerant-to-air heat exchangers (similar to a car radiator).

Reliability and efficiency are good reasons to buy a heat pump, but it is also the choice for environmental reasons. The U.S. Environmental Protection Agency (EPA) ranks ground source heat pumps as having the lowest overall environmental cost, and highest "source performance."