A plenum is a chamber or box used to distribute conditioned air from the main HVAC unit to the branch ducts serving different areas of a building. Plenums act as pressure vessels that equalize airflow and reduce velocity noise before air enters the ductwork system. They are typically located in attics, basements, or mechanical rooms immediately downstream of the air handler.
Design and Construction
Plenums are fabricated from galvanized steel, fiberglass board, or rigid foam with R-6 to R-8 insulation on exterior surfaces. Return air plenums are often constructed as the space above suspended ceilings, using the cavity as an air return chamber. Supply plenums typically measure 12 to 24 inches in depth and maintain internal velocities below 500 feet per minute.
Installation and Efficiency
Sealed and insulated plenums prevent air leakage and temperature loss, improving system efficiency by 5 to 15 percent. Proper plenum design reduces ductwork noise and pressure drops. Regular inspection for air leaks and blockages maintains optimal system performance and indoor air quality.