Traditional Heat Pumps Struggle in Cold Weather
A traditional air-to-air heat pump extracts heat from the outside, even during the winter, and brings it in the house. When outside air temperatures reach about 37 degrees Fahrenheit, however, the heat pump works constantly to keep the inside air temperature warm, Ask the Builder states. When outside temperatures lower, auxiliary electric coils help the heat pump warm the house.
Geothermal Heat Pumps Require Less Assistance
Geothermal heat pumps use the warmth of the soil 3 or 4 feet deep to heat and cool the house. Even at 20 degrees, the outside air temperature hardly affects the constant temperature of deep soil. This reduces the need for supplemental electric heat.
Heat pumps, whether air-to-air or geothermal models, must have an electric heat coil backup system. This system helps heat the house when temperatures drop to 30 degrees and below. Heat pumps can't keep up with 20 degree temperatures without auxiliary heating, unless the system uses geothermal heat.