Commercial Kitchen Hoods: Type I vs. Type II Requirements (IMC)
The short answer: Commercial kitchen exhaust hoods come in two types under the IMC (Chapter 5). A Type I hood is required over equipment that produces grease and smoke — fryers, griddles, ranges, charbroilers, woks — and must handle grease-laden vapors with grease filters, a grease-tight duct, and (for most cooking) a fire-suppression system. A Type II hood is for equipment that produces heat, steam, and moisture but not grease — dishwashers, steam kettles, ovens producing only steam, certain warewashing — and has simpler requirements. The trigger is the byproduct of the cooking process: grease and smoke mean Type I; heat and moisture alone mean Type II. Getting the type wrong is a common and consequential plan-review comment, because it changes ducting, fire protection, and makeup-air design.
The distinction: what the equipment produces
The hood type follows the cooking byproduct, not the equipment category in the abstract:
Type I — grease- and smoke-producing: fryers, griddles, ranges, charbroilers, broilers, woks, tilt skillets, rotisseries. These create grease-laden vapor that must be captured, filtered, and exhausted through grease-rated duct, with fire suppression for most cooking operations.
Type II — heat/steam/moisture without grease: commercial dishwashers, steamers, steam kettles, some ovens, and similar. These need exhaust for heat and humidity but not grease capture or (generally) suppression.
Core Type I requirements
A Type I installation typically involves grease filters/extractors, a continuous grease-tight (welded) exhaust duct, clearances or enclosure from combustibles, an exhaust fan sized to capture the cooking effluent, and a fire-suppression system interlocked to shut down fuel/power on activation. Makeup air must replace what the hood exhausts so the space isn't depressurized.
Core Type II requirements
Type II exhaust removes heat and moisture and is comparatively simple — no grease filtration or suppression — but still must be ducted and exhausted properly and balanced with makeup air.
Makeup air: the piece that gets missed
Whatever a hood exhausts must be replaced. Inadequate makeup air is a frequent comment: it causes negative pressure, doors that won't open, backdrafting, and poor hood capture. Makeup-air design is part of the hood package, not an afterthought.
Common review comments
Type II shown over grease-producing equipment (should be Type I).
No fire suppression indicated on a Type I hood over cooking equipment.
Missing or undersized makeup air.
Grease duct routing/clearance not addressed.
Exhaust requirements for kitchen equipment appear on the equipment schedule and affect connected load calculations for the exhaust fans and makeup-air units.