How Heat Pumps Work: The Refrigeration Cycle in Reverse
A heat pump is a device that moves thermal energy from a lower-temperature source (outdoor air, ground, or water) to a higher-temperature destination (indoor air or water) using a refrigeration cycle. Unlike electric resistance heaters (which convert 1 kWh of electricity into 1 kWh of heat — 100% efficiency), heat pumps move existing heat using electricity as the 'pump' driving the cycle — achieving Coefficient of Performance (COP) values of 2.0–5.0, meaning each kWh of electricity delivers 2–5 kWh of heating energy. The cycle: a cold low-pressure refrigerant (typically R-410A or the newer lower-GWP R-32 or R-454B) flows through an outdoor heat exchanger (evaporator) where it absorbs heat from the source and evaporates. A compressor increases the refrigerant's pressure and temperature. The now-hot high-pressure vapor flows to the indoor heat exchanger (condenser) where it releases heat to the indoor air or water and condenses back to liquid. An expansion valve drops the pressure, completing the cycle. The cycle reverses for cooling: the indoor coil becomes the evaporator (absorbing indoor heat), and the outdoor coil releases heat — exactly how air conditioning works. Modern heat pumps perform both heating and cooling functions with a single system, replacing both furnace and AC.