Grease duct

A grease duct is a duct that is specifically designed to vent grease-laden flammable vapors from commercial cooking equipment such as stoves, deep fryers, and woks to the outside of a building or mobile food preparation trailer. Grease ducts are regulated both in terms of their construction and maintenance, forming part of the building's passive fire protection system. The cleaning schedule is typically dictated by fire code or related safety regulations, and evidence of compliance must be kept on file by the owner.

Vapors are created when grease is heated to and beyond its vaporization point. As the vapors cool down, the grease condenses and settles on colder surfaces. It is thus important for occupational safety and health, as well as compliance with local fire codes, to vent such vapors outside the kitchen and outside the building where the kitchen is located.

Grease is not only slippery, but also a highly flammable hydrocarbon. Regardless of what state it is in, vapor, liquid or solid, it ignites easily and burns very rapidly. A fire-resistance rating is intended to certify resistance to an internal grease fire as well as an external fire. Any adjacent firestop must be compatible with the grease duct system.

In North America, grease ducts must be in compliance with NFPA 96 as well as the local building codes and fire codes. Grease ducts should be kept as short as possible to minimize grease build-up.

Internationally, grease ducts must be protected against weathering to prevent corrosion, and must be composed of specific materials based on the hood type. For example, commercial kitchen hoods should be of steel no thinner than .0575 inches. Duct joints must be welded flange joints, butt joints, or overlapping joints.

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