Galvanized Plenum We stock pre-fabbed plenums in 3 and 4 foot lengths that are designed to fit our line of Armstrong / AirEase equipment. SKU PLENUM1420 Product Details | Specifications | Check Inventory Please select 13.5 X 19.75 4' FLANGE PLENUM 16.5 X 19.75 4' FLANGE PLENUM 20"X19.75"X4' PLENUM (4PC) 23.5"X 19.75" 4' FLANGE PLENUM16.5 X 20 PLENUM 4' LENGTH 16 X 23.5" PLENUM 4'W/ END CAP19.5"X20"X4' PLENUM (2PC)L-SEC14X20 PLENUM 2 PC 16X20 PLENUM 2 PC 20X20 PLENUM 2 PC Log in to view price