Geothermal HVAC systems use the relatively constant temperature of the earth as a heat source in winter and a heat sink in summer. A network of pipes (a ground loop) circulates fluid underground, absorbing heat from the earth in winter and transferring it into the building. In the summer, the process reverses, A heat pump extracts heat from the home and transfers it to the cooler fluid, which is then dissipated into the ground. Geothermal heating and cooling is highly energy-efficient, although installation costs can be higher due to the ground loop installation. Geothermal systems reduce energy use and have a smaller carbon footprint.