Ground Source Heat

Ground source heat (geothermal heating) is a heating system that harnesses solar energy stored in the ground by using a heat pump to extract low-grade heat from the earth and upgrade it to temperatures suitable for building heating and domestic hot water. The heat is collected through a closed-loop pipe system filled with a water-glycol mixture, installed either in a vertical borehole (100 to 300 meters deep) or a horizontal ground loop (buried 1 to 2 meters deep over a large area).

Ground source heating offers the highest efficiency of any heat pump technology because the ground temperature remains relatively stable year-round — typically 5 to 8 degrees Celsius at borehole depths in Finland — providing a consistent heat source even during the coldest winter days. This stability gives ground-source systems a seasonal COP of 3 to 5, meaning they produce 3 to 5 kilowatt-hours of heat for every kilowatt-hour of electricity consumed.

The main barrier to ground source heating is the high upfront investment, particularly the cost of drilling boreholes (which can account for 30 to 50 percent of the total system cost). However, the lower operating costs compared to direct electric heating, oil, or even air-source heat pumps result in payback periods of 7 to 15 years. The system's expected lifespan is 20 to 30 years for the heat pump and 50 or more years for the ground loop.

Ground source systems require minimal maintenance once installed — there are no outdoor units to keep clear of snow, no defrost cycles, and the ground loop is maintenance-free. The heat pump unit itself should be serviced every 2 to 3 years, including checking the refrigerant circuit, compressor operation, and control system. If heating output declines, the issue is usually within the heat pump unit rather than the ground loop.