Geothermal technology is a new take on a recognizable process—the coils at the back of your fridge are a mini heat pump, removing heat from the interior to keep foods fresh and cool. In a home, geothermal or geoexchange

• pumps use the constant temperature of the earth (a few feet below the surface) to cool homes in summer and warm houses in winter—and even to heat water.
• Geothermal systems can be initially expensive to install but typically pay off within 5 to 10 years. They are also quieter, have fewer maintenance issues, and last longer than traditional air conditioners.