Clearance: A minimum amount 450mm clearance is encouraged with the cooking surface towards the underside of any grease filter. Grease Exhaust Duct Welded Joints Canopy hoods have necessities to increase a minimum of 6” beyond cooking surface, That is to ensure the entrainment of any warmth and smoke. UL 2221 https://grease-tight-extract-duct12234.humor-blog.com/35748456/the-ultimate-guide-to-grease-tight-extract-ductwork