A central air-to-air heat pump outside your home can remove heat from the ambient air and apply that heat to your home. Historically, below 20 degrees, air-source heat pumps drop in efficiency to 100 percent (no better that electric radiant heat). They do not drop below 100 percent efficiency.
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Do heat pumps really work in cold weather?
Heat pumps use the heat in the air or the ground around them as their main source of energy. The refrigerant can absorb heat even in extremely low temperatures of -20 °C, which is why heat pumps are able to work in cold climates. This evaporated refrigerant is then compressed, which increases the temperature further.
What temperature is too cold for heat pumps?
Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.
The COP continues to drop until we reach an outdoor temperature of -4°F (-20°C). -4°F is the lower limit of our air source heat pump effective temperature range. In temperatures lower than that the heat pump shuts down and electric backup heat takes over. The backup heat protects the compressor and preserves the longevity of the machine.
Heat Pump Temperature Lift