Air Handling Unit (AHU) is a machine used to circulate air as part of a heating, ventilating, and air-conditioning system. An Air Handling Unit is usually a large metal box containing a blower along with motor arrangement, cooling and heating coils, different types of filter chambers, and volume control dampers. Air handlers usually connect to the duct distribution system that distributes the conditioned air through the building and returns it to the AHU.