Abstract: The air-to-air split system or packaged heat pump system is used to heat and cool buildings. In the heating mode it extracts heat from the outside air for space heating. Heating and cooling with this type of heat pump is achieved by reversing the flow of refrigerant through the outdoor and indoor refrigerant coils. In the heating mode the outdoor coil acts as an evaporator and extracts heat from the air, the indoor coil acts as a condensor and gives off heat to the air handling system for the building. The reverse action takes place in the cooling mode. The operation of the reversing valve is controlled by a heating and cooling thermostat inside the building.This invention relates to the use of the described heat pump system in the heating mode in combination with the exhaust system for the building to extract heat from the building exhaust air, which is normally exhausted to the outside air without any heat removal.