Geothermal heating (known as Ground Source Heat Pumps, or GSHP’s) at its most basic is just transferring heat energy between the Earth and your home. In the winter when you need to heat, you simply transfer the heat from the earth into your home. In the summer when you need to cool, it is just the opposite; heat is taken from your house, and put back into the earth.
Geothermal systems can be installed basically anywhere, and have no need for natural hot springs or geysers under your house. This system just uses a heat exchanger in the earth to transfer the heat energy.
The United States E.P.A. has called ground source heat pumps
The most energy efficient, environmentally clean and cost effective space conditioning system available.
Geothermal systems provide highly efficient, clean, quiet and renewable heating and cooling at a very low cost.