Plenum Box

Truestar Air Systems

Plenum Box

In HVAC (Heating, Ventilation, and Air Conditioning) systems, a plenum box is a crucial part that aids in distributing air from the main duct to several branches or diffusers. It’s a junction box that acts as a bridge between a building’s numerous distribution points and the main ductwork. Plenum boxes have the following important characteristics and things to keep in mind:

Plenum Box

Function: A plenum box’s main job is to maintain a constant airflow rate and pressure by distributing air from the main duct to several branches or diffusers in an even and uniform manner. It makes sure that conditioned air efficiently reaches every part of the building and assists in balancing the airflow inside the HVAC system.

Construction: To provide strength, longevity, and corrosion resistance, plenum boxes are usually made of sheet metal, such as stainless steel, aluminium, or galvanised steel. Depending on the needs and application, they could include an insulating liner to reduce heat loss or condensation.


Design: To accommodate varying airflow requirements, duct sizes, and installation conditions, plenum boxes are available in a variety of designs and combinations. Based on the distribution layout and the main duct’s design, they can have a round, square, or rectangular shape. The HVAC system’s noise levels, air velocity, and pressure drop are all impacted by the plenum box’s design.

Connections: To accommodate the main duct, branch ducts, diffusers, and grilles, plenum boxes usually include several inlet and outlet connections. To make installation and connecting to other duct components simple, these connectors can be fitted with flanges, collars, or slip-fit connections.


Access: To facilitate the examination, cleaning, and upkeep of the inside components—such as dampers, filters, or insulation—some plenum boxes may have doors or access panels. Over the course of its life, effective servicing and maintenance of the plenum box are ensured by proper access.

Dampers: To control airflow to various branches or zones within the HVAC system, plenum boxes can come with dampers or louvres installed. These dampers aid in controlling the temperature distribution throughout the building and balancing the airflow.