If you are looking to reduce your energy costs and consumption, a geothermal HVAC system may be right for you: Most geothermal systems function using a ground-source heat pump. Loop piping is generally run underground either in vertical loops or horizontal loops. The system uses the Earth as a heat source in the winter and a heat sink in the summer. Since the soil below 6 feet is generally at a constant temperature between 40 and 60 degrees in this area, it can be used year round to help cool or heat a home. The system uses a heat pump to transfer the temperature of the fluid running through the underground piping to the air running through your HVAC system.