The minimal duct thickness is outlined by whatever code jurisdiction the project is situated in. Beneath are two code references related to the expected thickness and product variety for grease ducts. Overhang: The extraction canopy should overhang the cooking machines by not less than 250mm within the front and sides. https://grease-tight-extract-duct68900.onzeblog.com/37030218/details-fiction-and-grease-tight-extract-ductwork