What is Plenum in HVAC?

A plenum in heating, ventilation, and air conditioning (HVAC) systems is a box or volume in the building structure that connects to the HVAC system. It has a critical function and that is to bring in, distribute, or remove air.

 

Each HVAC system typically uses two plenum boxes: a supply plenum and a return plenum.

 

A supply plenum works by taking in the new cool or warm air from the heater or air conditioning system and, in turn, distributes it throughout the building using the HVAC’s ductwork.

 

A return plenum takes in that used room air and, using the ductwork sends it back to the core HVAC system. That air is filtered, cooled, and returned to the space.