Word of the Month: VAV Box

VAV box

With the temperature fluctuating quite a bit this Winter season, buildings are not immune to the need for frequent temperature adjustment. Luckily, our word of the month, the VAV box, will help explain what's going on inside the buildings. 

How does a VAV box work?

It is usually not cost effective to have one Heating, Ventilation, and Air Conditioning (HVAC) system to condition each zone or room in a building. Instead, larger HVAC systems will serve several zones or rooms. However, not every room in a zone has the same desired set point. This is where a VAV box comes in handy. Some rooms have a variable air volume terminal unit (aka VAV Box) that allows different volumes of air into a space to provide better control of the room temperature and air flow.

john in PES
John explains how the VAV boxes work in the Plant and Environmental Sciences building. 

Inside the VAV box, there is a damper that opens and closes to control the amount of air entering the room. If a room needs to cool further, the damper opens to its maximum position to allow high airflow and cool the room down to the appropriate temperature. Once the room reaches the desired temperature, the damper returns its minimum position.


vav components


Some VAV boxes have a reheat coil. If a room needs to be heated, a valve opens to allow heating water to flow through the reheat coil which reheats the air that passes through the coil. The controls that monitor air flow and heating coil are normally linked to the room’s thermostat. The controller communicates with the damper to determine the position and the amount of air that goes to the room. The controller also communicates with the reheat coil to determine if the air from the air handler needs to be heated to meet the thermostat’s set point for the room.


It is important to remember that there are several factors besides the VAV box that influence temperature and comfort.

  •  airflow and temperature into the room
  • outside temperatures
  • your level of physical activity


Although the VAV box is a key factor in maintaining airflow and temperature, your feedback is just as important. By using TherMOOstat, you can let us know how stuffy, hot or cold your space feels.