We get geothermal energy, which is clean sustainable heat, from the earth. This resource of energy ranges from shallow ground hot water to hot rock found miles below earth’s surface. As we go deeper, we find molten rock of extremely high temperatures called magma. About ten feet of earth’s shallow ground maintains a constant temperature of about 16 degrees C (60.8° F). Geothermal heat pumps are used to warm buildings from a network of heat exchanger pipes buried adjacent to buildings. This process is reversed in the summer to cool the buildings. This system provides a free source of hot air in winter and cool water during summer.