Retourplenum

Retourplenum, commonly referred to as a return plenum or plenum chamber, is a compartment within an HVAC system that collects air returning from occupied spaces and routes it back to the air handling unit for filtration and reconditioning. The term is used in various HVAC contexts to describe this dedicated room or ducted space.

It is typically located in ceiling voids, mechanical rooms, or under raised floors, connected to the return air ducts of the building's air handling equipment. Constructed from metal, often galvanized steel, the plenum walls are sealed to prevent air leaks into adjacent spaces and may be insulated or lined to control noise and thermal losses. Access panels allow inspection and cleaning.

During operation, air from rooms is drawn into the plenum through grille registers and diffusers and then transported by the return ducts to the air handling unit for filtration and conditioning. The plenum acts as a buffer that equalizes flow and helps reduce noise but must be designed to prevent contamination and to accommodate expected air volumes.

Design and safety considerations include fire resistance, acoustics, moisture control, and access for maintenance. Plenums must meet applicable codes and standards, such as local building codes and industry guidelines, and are often subject to inspections for cleanliness and leakage.

Maintenance typically involves periodic cleaning to remove dust, mold, and debris, inspection of joints and insulation, and verification that dampers and access panels operate correctly. Properly designed and maintained retourplenum systems contribute to efficient, safe, and quiet building ventilation.