An air plenum is a chamber or duct section designed to distribute, collect, or regulate airflow within an HVAC system. Common types include supply plenums that distribute conditioned air to multiple outlets and return air plenums that collect air from spaces back to the system. Properly designed plenums reduce air velocity, minimize noise, and improve system efficiency by 5 to 10 percent.
Design Specifications
Supply plenums typically maintain air velocities of 400 to 600 feet per minute to reduce turbulence and noise generation. Return air plenums operate at slightly higher velocities, around 500 to 700 FPM, depending on duct sizing. Plenum volume should be sized at 3 to 5 times the supply duct diameter to allow proper air settling.
Performance Benefits
Well-designed air plenums reduce pressure drop across the HVAC system, lowering fan energy consumption and operating costs. They also help equalize air temperature distribution and reduce noise transmission through ductwork. Proper plenum sizing is essential for achieving design airflow rates and maintaining indoor air quality standards.