How air handling units work

window air conditioner image by Aaron Kohr from

HVAC (Heating, Ventilation and Air Conditioning) systems refer to systems used to provide heating and cooling systems to buildings. Air handling units are an integral part of HVAC systems, and are designed to circulate and condition air.

Air Handling Unit Design

An air handling unit is typically comprised of a metal box containing heater or cooler elements, a blower, dampers and filter chambers or racks. Air handling units often connect to the ductwork system used to send conditioned air through a building and then return it to the handling unit. .


Air handling units often use a squirrel cage blower powered by the AC electric motor to circulate air. The air flow rate is controlled by vanes or dampers on the fan. Small air handling units also contain a fuel-burning heater or heat pump which is placed in the air stream to heat it. Larger air handling units use coils to circulate hot steam or water for heating, and circulate chilled water for cooling purposes.


Small air handling units, called terminal units, often contain only a blower, air filter and heater, and are used for local use. Larger air handling units that condition outside air are called make-up air units A packaged unit refers to an air handling unit exclusively designed for outside use, and is typically found on roofs.