The indoor HVAC unit is typically referred to as an air handler. An air handler is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. It is usually connected to a ductwork system that distributes the conditioned air through the building and returns it to the air handler. The air handler contains a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers.