iDEAL 31" Center Solid Duct Section for Semi Downdraft Paint BoothiDEAL 31" Center Solid Duct Section for Semi Downdraft Paint Booth PSB CNTRDUCT 31X36 iDEAL Semi Downdraft Paint Booth 31" Center Solid Duct Section extends 31" diameter Exhaust Duct Kit an additional 36" length. Recommended maximum of 3 sections for stability purposes. If customer needs more length, we would recommend the customer to locally source a longer 'spiral type' center ducting, which provides much more duct stack stability. For Use With