The refrigeration system within the heat pump is made up of a compressor and two coils of copper tubing, surrounded by aluminum fins aiding in the transfer of heat. The coils resemble a car radiator. As with refrigerators or an air conditioner, the refrigerant flows through the pipes, back and forth from the outdoor coils.
In heating mode, it extracts heat from the outside coils and moves it into the home as it evaporates into gas. The indoor coils transfer heat as it condenses back into a liquid. A reversing valve, located near the compressor, changes the direction in which the refrigerant flows for cooling in the summer or defrosting the outdoor coils in the winter.