Highest efficiency available
What makes geothermal heat pumps so outstanding is their efficiency. For example, the very best natural-gas furnaces provide about a 95% efficiency rate—meaning that for every dollar you spend on electricity and gas to heat your home, the furnace is able to return about 95 cents worth of heat. A geothermal system will give you more than four times that rate.
“You would have to look a long time before you get a fossil-fuel rate that would be competitive with geothermal,” says Terry Munyon, a director of the Iowa Geothermal Association. “It kicks butt. You are getting four units of energy out for every one that you buy.”
That efficiency translates in to savings. According to the U.S. Department of Energy, a geothermal system will save 50% to 70% of home energy usage for heating and cooling.
Warmth down below
A geothermal heat pump works by taking advantage of the naturally stable temperatures that occur a few feet below ground level—typically a steady 50-65°F all year long. In winter, when the temperature of the air is colder than the earth, a geothermal heat pump borrows heat from the earth to heat your home. In summer, the reverse is true. The heat pump uses the relatively low temperature of the earth to cool your home. A heat pump moves heat one direction or the other, which is how it gets its name.
The key component of a geothermal heat pump system is the loop field—a long length of plastic pipe that is buried underground either horizontally or suspended vertically in a series of holes drilled at least 200 feet deep. In winter, a pump circulates antifreeze fluid through the loop field where it picks up heat. Coils inside the pump extract the heat and use it to warm air. A fan blows this warmth through ductwork into your home. In summer, the cycle is reversed as the system extracts heat from inside a home and deposits it underground.
Despite its advantages, there’s still one major drawback to geothermal heat pumps. For an average 2,000 sq. ft. house, a geothermal heat pump system will cost in the neighborhood of $20,000—more than twice as much as a conventional heating and cooling system. Much of this steep upfront investment is due to the costs of installing the loop field. However, the system pays for this additional cost through energy savings in about a decade.
At least Uncle Sam is there to help you over the hump. Geothermal heat pumps qualify for the Residential Renewable Energy Tax Credit, which automatically knocks 30% off the installed price. Further deals may be available from energy utilities or your state government; check with the Database of State Incentives for Renewable Energy.
Geothermal systems are extremely quiet. Because there are so few moving parts, they are durable, reliable, and maintenance-free. Once installed, the loop field lasts indefinitely. The pump itself will last about 25 years; a replacement will set you back between $8,000 and $10,000.
Comparing various geothermal heat pumps can be a bit of a puzzle. Pumps come with separate performance ratings for their cooling and heating functions. Your best starting point is the Energy Star Geothermal Heat Pumps page, which lists certified products, and the Energy Efficiency and Renewable Energy guide published by the U.S. Department of Energy—which delves into the ratings in detail.
Owing to the complexities of properly sizing and balancing the system and ductwork—not to mention burying the loop in the ground correctly—geothermal is not a do-it-yourself project. Contact the International Ground Source Heat Pump Association or the Geothermal Heat Pump Consortium to find lists of contractors in your area.
Note that you don’t need a huge level area to be a candidate for geothermal, provided you have an area accessible to a well-drilling rig. An average home will need four bores, each about 15 feet apart, about 200 feet deep. Be sure to have all gas lines and other utilities marked beforehand. The drilling takes about half a day.
There’s another reason to consider geothermal heat pumps. Because they require only a trickle of electricity to power the pump and fan, they produce no CO2 emissions and help reduce demand for fossil fuels.