Geothermal HVAC systems use the relatively constant temperature of the earth as a heat exchange medium. During winter, heat from the ground warms the fluid, and this warmth is extracted by a heat pump and transferred indoors. In the summer, the process reverses, with the system transferring heat from the building to the ground. Geothermal HVAC 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.