Geothermal Heating Systems

Geothermal heat represents about two percent of the total heating market in the U.S., with more than 1.3 million systems installed. A geothermal system does not burn fossil fuels to create heat. It transfers heat. And that's its charm: To transfer heat takes less energy than to produce heat.

How Geothermal Systems Work
To harness the heat stored in the earth, a geothermal system captures and converts that heat for use in the home. System components include a loop of pipe, a liquid to absorb and transfer heat, and a heat-pump unit to process the heat for use. To capture heat, liquid circulates through a pipe buried in the ground. As it circulates, it absorbs the earth's stored heat, which remains constant at 50 to 60 degrees Fahrenheit 10 feet below ground level.

The heated liquid enters a heat pump unit. In this unit, the heat from the piped liquid is absorbed by a liquid refrigerant sealed in the unit. That refrigerant evaporates and is compressed, which raises its temperature to about 100 degrees Fahrenheit.

Now a gas, the refrigerant passes through a heat exchanger where the heat is removed and pumped into the house. With the heat removed, the refrigerant cools. It returns to its liquid state and continues to circulate, continually absorbing and using the heat transferred from the earth through the piped liquid.

Efficient, Low-Maintenance Heating
Geothermal heat pumps have become quite efficient. Their heating efficiency is indicated by the coefficient of performance, or COP, the ratio of heat provided per British thermal unit (Btu) of energy input.

Energy Star-rated heat pumps have a heating COP starting at 2.8, meaning for every unit of energy used to power the system, 2.8 units of heat are supplied.

Geothermal systems are simple to maintain. A properly installed and buried loop can last nearly 50 years. The mechanicals are installed indoors and typically require only periodic checks and filter changes.

Closed-Loop Systems
Geothermal heating systems operate as either closed-loop or open-loop configurations. Determining which loop to use depends on site factors like soil composition, landscaping, and underground utilities.

A closed loop uses the liquid solution in a sealed piping loop installed horizontally or vertically underground. 

Horizontal loops are used when there is enough usable land available. Pipes are installed in trenches dug about six feet deep and 100 to 600 feet long, depending on the size of the system. 

Vertical loops are the only choice when there is limited space available, if the homeowner does not want landscape disturbed, or where many rocks would be encountered when digging. To install the pipe, small-diameter holes 100 to 400 feet deep are bored using well-drilling equipment. Vertical loops are connected to the house via a horizontal underground pipe. When boring for vertical loops, well-drilling codes apply.

A sealed system can also be placed at the bottom of a pond if there is a pond available on the property. Pond loops may be the most economical option because much of the excavation cost can be eliminated.