What is the definition of a VAV unit? VAV stands for Variable Air Volume, and it is a type of heating, ventilation, and air conditioning (HVAC) system. VAV systems use a single control device, such as a thermostat, to regulate the temperature in multiple zones within a building, rather than relying on separate systems for each room or area. A VAV unit typically consists of one or more air-handling units, or AHUs, that draw in outside air and filter it to provide clean air to the building. Inside the AHU, the air is heated or cooled before it is distributed through ductwork that runs throughout the building. Each zone has its own VAV box, which controls the amount of air delivered to that area. The VAV box is attached to a controller, usually a thermostat, which communicates with the AHU to adjust the temperature in the zone.