Commercial Cooking Hoods & Duct Clearances

• Commercial cooking hoods for collecting cooking vapors and residues must be constructed of and supported by steel not less than 0.048 inches in thickness.
• All seams, joints, penetrations, and duct-to-hood collar connections for exhaust duct systems require liquid-tight continuous external welds.
• Filters for exhaust duct systems must be 4 feet above the appliance cooking surface.
• Rooftop terminations need a minimum of 10 feet of clearance from the outlet to adjacent buildings, property lines, and air intakes.
• A vertical separation is allowed if space limitations prevent a 10-foot horizontal separation from an air intake: the exhaust outlet should be a minimum of 3 feet above any air intake within 10 feet horizontally.
• The air velocity through any duct shall be not less than 500 feet per minute.

Clearances for Hoods, Grease Removal, and Ducts

• Hoods, grease removal devices, exhaust fans, and ducts must maintain a clearance of at least 18 inches to combustible material, 3 inches to limited combustible material, and 0 inches to noncombustible, except where enclosures are needed.
• When the distance is less than 18 inches between a grease removal device and the appliance flue outlet, install a steel or stainless steel baffle plate located not less than 6 inches from the grease removal devices.
• The replacement air quantity in exhaust fan systems must be adequate to prevent negative pressures in commercial cooking areas from exceeding 0.02-inch water column.
• A duct system for removing cooking vapors (passing through six floors of a multi-story building) needs to be installed in an enclosure having a fire resistance rating of at least 2 hours.
• Roofing terminations should have exhaust flow directed up and away from the roof surface, and a minimum of 40 inches above the roof surface.
• A solid-fuel cooking device is not permitted within 3 feet of any deep fat frying unit.
• Grease filters must be installed at an angle not less than 45 degrees from the horizontal.
• Deep fat fryers in commercial establishments need a separate high-limit control to shut off fuel or energy when the fat temperature reaches 475 degrees Fahrenheit at 1 inch below the surface.
• The duct leaving the hood should be no less than 18 gage stainless steel.
• All deep-fat fryers need at least 16-inch space between the fryer and surface flames from adjacent cooking equipment.
• Replacement air quantity must be adequate to prevent negative pressures in the commercial cooking area(s) from exceeding 4.98 Pa.
• Deep-fat fryers should have separate high-limit controls to shut off fuel or energy when the temperature reaches 475°F at one inch below the surface.
• No solid fuel cooking device should be used for deep-fat frying involving more than 1 quart of liquid shortening.
• A range hood exhaust duct passing through six floors of a high-rise apartment building must be installed in an enclosure with a fire resistance rating of at least 2 hour(s).
• Hoods with dampers in the exhaust need an access panel to be located within 18 inches of the damper.
• A building 10 feet tall with a rooftop mount exhaust system should have a velocity pressure of 500.
• Wall terminations through a noncombustible wall should have a clearance of 10 feet from the outlet to adjacent buildings.
• All deep fat fryers should be installed with at least 16 inches of space between the fryer and surface flames.
• The closest point of any air intake above the plane of the exhaust termination should be a minimum of 10 feet.
• Replacement air should always be adequate to prevent negative pressures in commercial cooking from exceeding 4.98 Pa.
• Clearance from the duct to the interior surface of a limited combustible should not be less than 6 inches.
• The minimum clearance between a duct conveying grease and an outside air intake should be 10 feet.