A heat pump is a mechanical-compression cycle refrigeration system that can be reversed to either heat or cool a controlled space. Think of a heat pump as a heat transporter constantly moving warm air from one place to another, to where it’s needed or not needed, depending on the season. Even in air that seems too cold, heat energy is present. When it’s cold outside, a heat pump extracts what outside heat is available and transfers it inside. When it’s warm outside, it reverses directions and acts like an air conditioner, removing heat from your home.