Geothermal Heating and Cooling Systems

Efficiency Maine offers incentives up to $3,000 through the Home Energy Savings Program for best in class geothermal systems that meet EPA Energy Star Tier 3 Criteria (also called ground source heat, ground source heat pumps, or geothermal heat pumps). Geothermal systems take advantage of the constant temperature of the ground below the frost line to heat in the winter and cool in the summer. Like all heat pump technologies, geothermal systems don’t create heat, they move it using the same process as standard air conditioners and refrigerators. In the winter, heat is drawn from underground and is transferred to the house. In the summer, the process is reversed to remove heat from the house and transfer heat to the ground.

Source: EPA (
  1. Water or a refrigerant moves through a loop of pipes.
  2. When the weather is cold, the water or refrigerant heats up as it travels through the part of the loop that’s buried underground.
  3. Once it gets back above ground, the warmed water or refrigerant transfers heat into the building.
  4. The water or refrigerant cools down after its heat is transferred. It is pumped back underground where it heats up once more, starting the process again.
  5. On a hot day, the system can run in reverse. The water or refrigerant cools the building and then is pumped underground where extra heat is transferred to the ground around the pipes.

This reversible refrigeration cycle process is one of the most efficient ways of heating and cooling your home. Geothermal heat pumps are typically more efficient than air source heat pumps because the temperature of the ground is moderate and closer to the desired indoor temperature year round than outdoor air temperatures. One unit of electricity translates into four or more units of heat with a geothermal heat pump. Like air source heat pumps, geothermal systems are good at keeping temperatures and humidity levels constant inside, making homes more comfortable and interior temperatures more predictable than with conventional heating systems.

Geothermal systems come in a number of different configurations. Typically, they are characterized first by the style of ground loop system and second by the heat pump unit. Geothermal systems transfer heat through loops of tubing called “ground loops.” Water or a glycol solution is circulated through ground loops warming the liquid to the consistent temperature of the Earth. Depending on your site and installation needs, loops can be configured in a shallow field, integrated with your water well, or more commonly in Maine, inserted into deep wells drilled exclusively for the geothermal system. Occasionally, a site’s water well may have sufficient depth, flow and volume to support geothermal heating. The cost of installing the ground loop system can vary significantly, and the size of the loop system will be determined by your home’s heating and cooling needs. Please note that ground loop installations in Maine must be sized to the heating load to avoid freezing the ground around the loops; this may reduce heat transfer efficiency during other times of the year.

Geothermal systems are also defined by the heat pump unit: the ground loop system delivers heat and cooling to your home via a heat pump unit that is typically located in the basement. The heat pump can deliver heat through a hydronic or forced hot air distribution system, and some heat pumps can also provide domestic hot water using a heat exchanger often referred to as a desuperheater.


  1. Low-cost heat — The cost of heating with a geothermal system is typically less than the cost of heating with oil, kerosene, electric baseboard or propane. Click here to compare heating costs of different heating systems.
  2. Low-cost cooling — Geothermal systems have low operating costs and meet heating and cooling needs with one system.
  3. Indoor comfort — Geothermal systems provide consistent indoor temperature and humidity levels and typically operate very quietly.
  4. Predictable energy costs — Geothermal systems can produce heating and cooling at a predictable rate of electric consumption. Some people couple PV systems with geothermal systems to offset this electric demand.
  5. Financing — Low-interest financing is available through Efficiency Maine for geothermal systems. Homeowners may also be eligible for a 30% Federal Tax Credit.
  6. Environmental Impact — Reduce the carbon footprint of your home or business by producing heating and cooling on site with the renewable resource of your yard.
  7. Safety — Because geothermal systems are electrically powered, there is no risk of combustion gas leaks.
  8. Durability — Geothermal systems are typically warrantied for 20 years or more. Loop fields can have a much longer life.


  1. Installation costs — Depending on your yard and the installation configuration chosen, geothermal systems are frequently more expensive to install than conventional heating or cooling systems. Pairing geothermal installations with air sealing, insulation, and other building envelope measures can reduce the size of the system needed and reduce installation costs.
  2. Siting — Not all buildings or yards are good candidates for geothermal systems. Ask a local professional for a site assessment to determine if you might be a good candidate for a geothermal system.

Taking Action

  1. Registered Geothermal InstallersClick here to find some installers in your area that sell geothermal systems.
  2. Get incentives and financing for energy upgradesClick here to find out about loans and incentives for projects that include energy assessments, air sealing, insulation, geothermal systems and more.
  3. Cost of Heating Comparison CalculatorClick here to find out how much you could save by switching to a geothermal system.