Jet Cowl

Jet cowls for spiral ducting, available in 16 diameters from 250mm to 1000mm. A jet cowl is a discharge terminal, not a weather cap: its geometry throws the extract plume vertically upward at speed — carrying solvent-laden air, fumes and process discharge clear of the roof, away from windows, air intakes and neighbouring buildings — while still resisting rain entry.

Why a jet cowl for spray booths and LEV

Local Exhaust Ventilation (LEV) systems — including spray booth, finishing and paint-mixing-room extract — must discharge to atmosphere so the contaminant disperses rather than falling back to ground or re-entering the building. HSE guidance HSG258 is explicit that a traditional capped cowl, which deflects discharge downwards, should not be fitted to an LEV stack: it prevents dispersion and risks contaminated air re-entering through openings and intakes. The jet cowl is the alternative it points to — vertical, high-velocity discharge with weather protection built into the shape. As the terminal on extract ductwork specified to the BESA DW/144 standard, it completes the stack at roof level.

When to specify one

Choose a jet cowl for any discharge you actively want dispersed: spray booth and finishing extract, commercial kitchen extract stacks, fume and process extract, and dust extraction returns. The size run — 250, 280, 300, 315, 355, 400, 450, 500, 560, 600, 630, 710, 762, 800, 900 and 1000mm — covers serious commercial and industrial stacks.

Complete the roof penetration with a Master Flash roof flashing and support the stack with matching bracketry. Every size is made to order — despatched in 3-5 working days up to 500mm, and 5-7 working days above.