What is the definition of an air handler? An air handler, also known as an air-handling unit, is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler consists of a blower, heating and/or cooling elements, filters, sound attenuators, and dampers. The blower is used to draw air into the air handler, which is then moved through the system components. Heating elements, such as electric heaters or a gas furnace, are used to heat the air. Cooling elements, such as an evaporator coil, are used to cool the air. Filters are used to remove airborne particles such as dirt, dust, and pollen from the air. Sound attenuators are designed to reduce the sound of the blower and other components. Dampers are used to regulate the flow of air in the system. An air handler