When a Type 1 Grease Hood Is Required
A Type 1 grease hood is required wherever a commercial cooking appliance produces grease-laden vapors or smoke. That covers most of the hot line in a full-service restaurant: fryers, griddles, charbroilers, open-burner ranges, woks, tilting skillets, salamanders and rotisseries. If grease can condense out of the cooking plume, the code expects it to be captured by a Type I hood, separated by listed filters and carried away in a grease duct.
The trigger is the cooking process, not the size of the restaurant. A small café with one countertop griddle cooking burgers needs a grease hood over that griddle. A large bakery running only convection ovens might not. When an appliance is in a gray area, such as a conveyor pizza oven or a combi oven that roasts fatty proteins, the manufacturer documentation and the authority having jurisdiction (AHJ) decide. Designs are prepared with NFPA 96 and the locally adopted mechanical code in mind, and the AHJ has the final say.
If your equipment only produces heat and steam, a Type 2 hood may be the better fit. The side-by-side breakdown is in our Type 1 vs Type 2 hood guide.
Anatomy of a Type I Grease Hood
A Type I hood is more than a stainless canopy. Each part has a job, and inspectors check most of them by name.
Capture area and canopy
The canopy forms a reservoir that holds the rising plume long enough for the exhaust to draw it through the filters. Depth, front height and the internal volume all affect how well the hood handles surges, such as a basket of frozen fries dropped into hot oil.
Filter bank and plenum
Grease filters sit in a sloped bank at the back of the canopy. Behind them is the exhaust plenum, a sealed chamber that collects filtered air and feeds it to the duct collar. The filter bank is set at a steep angle so captured grease runs down into the trough rather than dripping back onto the cooking surface.
Grease trough and cup
A trough along the base of the filters gathers grease and drains it to a removable cup or container. Kitchen staff empty and clean it on a routine schedule.
Lights and penetrations
Light fixtures are enclosed and gasketed. Any penetration through the hood, such as for suppression piping or wiring, must be sealed with a listed device or welded so grease cannot escape into concealed space.
Duct collar
The exhaust collar on top of the hood is welded liquid-tight to the grease duct. This joint is where the hood stops and the duct system starts.
Grease Filters for Type 1 Hoods
Type I hoods use listed grease filters, and in most kitchens that means stainless steel baffle filters. A baffle filter forces the air to change direction several times; grease droplets are thrown against the metal, collect and drain to the trough. Baffles also act as a flame barrier between the cooking surface and the plenum.
Mesh filters of the kind found on residential range hoods are not accepted as the primary grease filter in a Type I hood. They load quickly, hold grease in the media and can feed a fire instead of stopping it.
| Filter or device | Where it fits | Trade-off |
|---|---|---|
| Stainless baffle filter | Standard choice for most Type I hoods | Durable, dishwasher-cleanable, moderate grease removal on fine particles |
| Aluminum baffle filter | Budget installations | Lighter to handle but less resistant to harsh cleaners |
| High-efficiency or multi-stage filters | Heavy grease loads, long duct runs, odor-sensitive sites | Better capture of small particles, higher pressure drop and cost |
| Water-wash extraction section | Large, high-volume kitchens | Automatic cleaning cycle, needs water, drain and controls |
Filter count and size are chosen so the air velocity through each filter stays inside the listing range. Too few filters raises pressure drop and noise. Too many filters at low velocity lets grease pass through without impacting the baffles.
Fire Suppression Built Into the Grease Hood
Every Type I hood protects appliances that can ignite, so the hood is designed around a fire suppression system from the start. The common choice is a pre-engineered wet chemical system that meets UL 300. It covers three zones: the appliance cooking surfaces, the hood plenum behind the filters, and the entrance to the exhaust duct.
When the system detects a fire, through fusible links or electronic detection, it discharges agent through fixed nozzles and shuts off gas or electric power to every appliance under the hood. A manual pull station is mounted along the egress path so staff can trigger the system without reaching across the line. Gas supply is interrupted with a mechanical or electrically operated shutoff valve.
A few design points we settle before fabrication:
- Nozzle locations matched to final appliance positions, since moving a fryer later can leave it unprotected.
- Space and a mounting location for the agent tank cabinet, usually on the end of the hood or a nearby wall.
- Interlocks so the exhaust fan keeps running during a discharge (unless the system design calls otherwise) and make-up air stops if required.
- A portable Class K extinguisher near the line, which most fire marshals expect alongside the fixed system.
The suppression system is installed and certified by a licensed contractor authorized by its manufacturer. Ongoing inspection is covered on our hood service and maintenance page.
Exhaust Rates and Appliance Duty for Type I Hoods
The exhaust rate of a Type I hood is set by the hottest, greasiest appliance beneath it and by the hood style. ASHRAE 154 sorts cooking equipment into duty classes, and both listed hood data and code tables build on that idea.
| Duty class | Typical appliances | Plume character |
|---|---|---|
| Light | Gas and electric ovens, steam kettles, pasta cookers | Low heat, little grease |
| Medium | Fryers, griddles, open-burner ranges, tilting skillets | Steady heat with moderate grease |
| Heavy | Gas charbroilers, upright and chain broilers, wok ranges | Strong, turbulent plume with heavy smoke and grease |
| Extra-heavy | Solid-fuel equipment burning wood or charcoal | Very hot, smoky, often with sparks |
These groupings are typical; confirm them against the edition of the code adopted locally and the appliance manufacturer data. Listed hoods are tested at specific airflows, so the listing may permit lower exhaust than the default code tables. That saving carries through to a smaller fan and less make-up air.
Solid-fuel appliances have extra requirements, including separate exhaust in many cases and more frequent inspection. We treat them as their own design problem rather than adding them to a shared hood.
Listed vs Code-Built Grease Hoods
A Type I hood can be approved in two ways: as a listed hood tested to UL 710, or as an unlisted hood built to the prescriptive construction rules of the mechanical code and NFPA 96.
Listed hoods carry a label from a testing laboratory. The listing documents tested exhaust rates, clearance to combustibles and installation instructions. Inspectors generally accept those values as long as the hood is installed exactly as the listing describes.
Code-built hoods follow the material, joint, clearance and airflow requirements written into the code. They are common for very long hoods, unusual shapes and retrofits where a listed product will not fit. The exhaust rate usually comes from the code tables, which can mean more airflow than a comparable listed hood.
Either path can pass inspection. The choice depends on the AHJ, the shape of the space and how much exhaust air the building can afford to move. Unusual geometry is where custom hood fabrication earns its keep.
Connecting the Grease Hood to Duct, Fan and Make-Up Air
The grease hood only performs if the system behind it is right. From the collar up, the duct carries hot, grease-laden air that can ignite, so it is built to a stricter standard than any other duct in the building.
- Duct construction: commonly at least 16 gauge carbon steel or 18 gauge stainless, with continuously liquid-tight welded joints.
- Velocity: a minimum of 500 fpm is the commonly referenced floor, with many designs in the 1,500 to 1,800 fpm range to keep grease moving.
- Clearance: commonly 18 inches to combustible construction, reducible with listed wraps or enclosures.
- Access: cleanout doors at changes of direction and along horizontal runs.
Confirm these values against the edition adopted locally. Duct routing details are covered on the grease duct systems page.
Many jurisdictions now expect the exhaust fan to start automatically when cooking appliances turn on, usually through temperature sensors at the hood collar. Make-up air is interlocked with the exhaust so the kitchen stays slightly negative to the dining room without pulling hard on doors.
Daily Care That Keeps a Type I Hood Passing Inspection
Most grease hood failures at inspection trace back to housekeeping, not design. A few habits make the difference:
- Pull and wash baffle filters on a schedule that matches the cooking volume, often daily for fryer and charbroiler lines.
- Empty the grease cup before it overflows into the trough.
- Never run the line with filters missing; the plenum is not designed to be exposed to open flame.
- Keep the suppression nozzle caps in place and the pull station clear.
- Book professional cleaning of the hood, duct and fan at the frequency NFPA 96 sets for your cooking volume.
Ready to price a grease hood? Send your equipment list and floor plan through the quote request and an engineer will size the hood, filters and exhaust.
Type I Grease Hood Questions
- Does a countertop fryer or griddle need a Type I hood?
- In most jurisdictions, yes. Fryers and griddles release grease-laden vapor regardless of size, so they typically need a Type I hood with listed filters and fire suppression. Some electric countertop units are listed for use with recirculating or ventless systems, but that approval depends on the specific product listing and the local AHJ.
- Can I install a Type I hood myself and add suppression later?
- It is not a good plan. The hood must be built with openings, piping routes and space for the suppression system, and the nozzles must be laid out for the final appliance positions. Inspectors usually check hood, suppression and gas shutoff together. Adding suppression after the fact often means field modifications to the hood.
- How often should Type I hood filters be cleaned?
- Filter cleaning depends on cooking volume. Kitchens running fryers and charbroilers all day often wash baffle filters daily or every other day, while lighter operations may manage weekly. Heavy grease on filters raises pressure drop, reduces airflow and increases fire risk, so check them often during the first weeks and set a schedule from what you see.
- What is the difference between a listed and an unlisted grease hood?
- A listed hood has been tested by a laboratory to UL 710 and carries a label with tested airflows, clearances and installation instructions. An unlisted hood is built to the construction rules written in the mechanical code and NFPA 96 and usually uses the code table exhaust rates. Both can be approved by the AHJ.
- Why does my grease hood need so much exhaust air?
- Heavy duty appliances such as charbroilers and woks produce a hot, turbulent plume that rises fast and spreads wide. The hood needs enough airflow to contain the surge before it rolls out of the front. Listed hoods, side panels, good make-up air placement and putting the heaviest appliance in the middle of the line can all reduce the required airflow.
- Can two restaurants share one grease duct and fan?
- Shared grease exhaust between separate tenants is restricted under NFPA 96 and many local codes, and where it is allowed it requires specific design measures and AHJ approval. In food halls and multi-tenant buildings each cook line usually gets its own hood, duct and fan, or a carefully engineered shared system reviewed in advance.