An Air handler, or air handling unit, is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning system. An air handler is usually a large metal box containing a blower, furnace or A/C elements, filter racks or chambers, sound attenuators, and dampers. The air handling unit (AHU) is the heart of central air conditioning. It collects outside air and room air, removes dust and other particles from the collected air, adjusts the temperature and humidity and then supplies comfortable and refreshing air-conditioned air into the rooms through ducts.

An Air handling unit (AHU) is a machine that conditions (i.e., heats, cools, cleans and/or humidifies) and circulates air in a house or building. AHUs are components of complete heating, ventilation, and air conditioning (HVAC) systems.