The technical guidance on this page reflects these published codes and standards, which your local authority (AHJ) adopts, amends, and enforces. It is educational, not engineering or legal advice — confirm the current requirements for your jurisdiction.
A Type I hood handles grease and smoke from fryers, ranges, griddles, and charbroilers; it needs grease filters, grease-rated ductwork, and a fire-suppression system. A Type II hood handles only heat, steam, and moisture from dishwashers, steamers, and some ovens, with no grease duct or suppression required.
Under the International Mechanical Code (IMC) Section 507, commercial kitchen hoods are classified by what the appliance beneath them produces. A Type I hood is required where cooking equipment produces grease or smoke. A Type II hood is used over equipment that produces heat, steam, or moisture (or products of combustion) but no grease or smoke.
That single distinction — grease versus no grease — drives everything else: filters, duct construction, fire suppression, cleaning schedules, and cost. Getting the classification wrong is not just an inspection failure; a heat-only Type II hood installed over a fryer would have no grease filters and no fire-suppression system over a serious fire hazard.
Type I hoods go over grease- and smoke-producing appliances: deep fryers, open-flame ranges, griddles, charbroilers, woks, rotisseries, tilt skillets, and most non-microwave ovens used for high-volume cooking. Because they capture airborne grease, Type I systems are built for containment and cleaning.
Required features of a Type I system include:
Type I hoods also carry the heaviest maintenance obligations, including scheduled exhaust-system cleaning under NFPA 96 based on how much grease the kitchen produces.
Type II hoods are for appliances that give off heat and moisture but not grease: commercial dishwashers, booster heaters, steam tables, steamers, pasta cookers, and ovens or kettles that produce steam or products of combustion without grease-laden vapor. There are two common subtypes in practice — condensate (dishwasher) hoods for steam, and heat/fume hoods for combustion products.
Because there is no grease to capture, Type II hoods are much simpler: they generally do not require grease filters, grease-rated welded duct, or a fire-suppression system. The IMC still requires the interior to have smooth, cleanable, water-tight joints and seams, and some heat-and-moisture loads can be handled by the building's HVAC design instead of a dedicated hood where the code allows. This is why Type II systems cost meaningfully less to install and maintain than Type I.
The reason Type I hoods are expensive is what happens above them. Grease duct under NFPA 96 must be liquid-tight and continuously welded, sloped to drain, provided with access panels for cleaning, and kept clear of combustible materials or protected by rated enclosure/wrap. The exhaust fan, duct, and hood plenum must all be cleanable and inspected on a schedule tied to grease volume.
Fire suppression is equally strict. A Type I hood typically carries a pre-engineered wet-chemical system listed to UL 300, with nozzles aimed at each appliance and at the plenum and duct, fusible-link heat detection, a manual pull station, and automatic shutoff of gas and electric power to the appliances when it discharges. These systems require semiannual inspection under NFPA 96 / NFPA 17A. None of this applies to a Type II hood — which is exactly why the classification matters so much.
Some electric appliances can be used without a ducted hood if they use a factory-built recirculating system listed and labeled to UL 710B. These "ventless" units pull cooking effluent through built-in grease filtration and often catalytic and HEPA/charcoal stages, then return cleaned air to the room instead of ducting it outside. When listed to UL 710B and installed per the IMC, such systems are permitted without a separate NFPA 96 hood-and-duct system.
Important limits apply: recirculating systems are for electric appliances only, because their filters do not remove the products of combustion from gas equipment. Local authorities do not always accept ventless cooking, listings restrict which appliances and menu items are covered, and the units still demand diligent filter maintenance. Always confirm acceptance with your local code official before relying on a ventless solution.
| Factor | Type I | Type II |
|---|---|---|
| Produces | Grease and smoke | Heat, steam, moisture (no grease) |
| Typical appliances | Fryers, ranges, griddles, charbroilers, woks | Dishwashers, steamers, booster heaters, some ovens |
| Grease filters/baffles | Required | Not required |
| Ductwork | Welded, liquid-tight, NFPA 96 grease duct | Simple, no grease-duct rules |
| Fire suppression | Required (UL 300 wet chemical) | Not required |
| Governing code | IMC 507, NFPA 96, NFPA 17A | IMC 507.3 |
| Relative cost | High | Low |
When in doubt, classify by grease: if the appliance can throw grease into the airstream, plan for a Type I system.