What serves as the heat source for an air-to-air heat pump?

An air-to-air heat pump utilizes outside air as its primary heat source. This system operates by extracting heat from the ambient air, even in cold temperatures, and transferring it indoors to provide heating. Since the heat pump can absorb heat from the air, it functions efficiently across a range of outdoor conditions.

When the temperature outside is lower, the heat pump employs refrigeration principles to absorb heat from the outside air and deliver it inside. This process is made effective by using refrigerants that evaporate at low temperatures, allowing them to extract heat from the air efficiently. Thus, outside air is the key component that enables the system to provide heating to a building.

Other heat sources listed, like ground temperature, electrical resistors, and thermal panels, pertain to different types of heating systems or methods but do not apply to the operation of an air-to-air heat pump. Ground temperature relates to geothermal systems, while electrical resistors serve as a backup heating method, and thermal panels typically refer to solar heating systems.