Earth is brimming with a limitless source of energy -- geothermal. Deep inside the planet is a lot of hot water and steam. The deeper you go, the hotter it gets. But you don't have to dig too deep to take advantage of this energy. Only a few feet below the surface, the temperature of the water remains constant year round, generally about 42 to 80 degrees Fahrenheit (5.56 to 26.67 Celsius) depending on where you live. A geo-exchange system can use this energy to heat and cool almost any kind of building [source: Minnesota Geothermal Solutions].
Geothermal systems do not directly tap into the heat inside the Earth. Instead, geothermal homes use heat pumps to take advantage of the constant temperature of geothermal wells under the ground. The heat pump can cool a house in the summer and warm it during the winter. Heat pumps have a fluid inside, which could be water or a refrigerant. When it is cold outside, the fluid absorbs Earth's heat and brings it inside to warm the air. In the summertime, the heat exchange works in reverse, cooling the house [source: APH Geothermal].