Geothermal heating is a method of heating and cooling a building. It takes advantage of the natural stable warmth stored in the earth. Normally the earth is around 55°F (12.8°C). This is accomplished by one of a number of methods. A heat pump uses the extracted water or transfer fluid as a heat source in winter and a heat sink in summer. Some systems use part of the heat to heat the building's hot water.

Types of geothermal systems

• Long, shallow loops buried in the ground
• Pipes circulating fluid through or drawing water from a nearby body of water
• Deep wells - usually two or more wells over 200 feet deep

Either of these systems can be either open-loop or closed loop. In a closed system, water and antifreeze (or other tranfer fluid) is circulated through the heat exchanger and back out through the loops continuously. In an open system, water is drawn from depth in a deep well system or from a body of water in a shallow system. Once this water passes through the heat pump, it is released back to its source, generally as far from the intake as possible. Some closed loop systems bled off a portion of their working fluid to keep the source temperature stable.

Geothermal heating is one of the most efficient ways to heat a building but it has high initial costs for drilling the wells deep enough into the earth to take advantage of the earth's temperature. It also has ongoing costs for the electricity to power the pump and heat pump.

See also geothermal energy, Deep lake water cooling

Some actually useful information, including DIY cookbooks: http://geoheat.oit.edu/pdf/pdfindex.htm