One of the most energy-efficient options for heating and cooling your home draws on another form of renewable energy—geothermal energy, or heat from the earth. This is not the hot steam and heat that comes from deep underground (discussed here). Rather, geothermal heat pumps draw on the relatively stable temperatures of the ground surrounding your home as a source of heat in the winter and cooling in the summer.
Geothermal heat pumps are usually installed when a house is built, because they require the installation of a large loop of tubing at least several feet under the surface. For some systems, narrow trenches are dug to install the tubing; other systems use vertical loops that can be installed much like drilling a well—a simpler process for retrofits to existing homes.
Some models also use geothermal energy to heat water for your home. These so-called “hydronic” systems save you money by eliminating the need for a separate water heater and save energy by heating water efficiently.
Just as a refrigerator uses electricity to keep the inside cool, while releasing heat into your kitchen, a geothermal heat pump can keep the inside of your home cool while releasing heat into the cool earth. In the winter, this process is reversed, so the geothermal heat pump draws heat from the earth and releases it into your home.
Because geothermal heat pumps actually move heat between your home and the earth, rather than creating heat by burning fuels, they operate very cleanly and efficiently. In fact, geothermal heat pumps are at least three times more efficient than the most energy efficient furnaces on the market today.
The relatively stable temperatures of the ground allow geothermal heat pumps to operate more efficiently than conventional air-source heat pumps, which exchange heat from the home with the outside air rather than the ground. During hot summer days, it’s much easier to release heat into the cool earth than into the hot air. Likewise, during frigid winter days, it’s easier to draw heat from the ground than from the much colder air. For these reasons, geothermal heat pumps operate efficiently even in harsh climates.
Airsource heat pumps and high-efficiency gas furnaces can heat homes efficiently while minimizing air pollution. These options are often twice as efficient, and much cleaner, than older boilers and furnaces.
Look for the Energy Star®label when buying new heating and cooling equipment, and also check the EnergyGuide label. Although the minimum furnace efficiency is set at 78% by U.S. law, some models can achieve efficiencies as high as 95%.
There is another abundant source of renewable energy that might work for your home: wood heat. Today’s modern wood stoves can generate heat efficiently from wood with low emissions.