What type of cooking equipment will the hood cover?
What sits under the hood determines the exhaust hood you need. The hood type, airflow rate, and filter selection all change based on whether the equipment produces heavy grease, high heat, smoke, steam, or just dry warmth. Matching the hood to the cooking process keeps the air clear and stops the ductwork becoming a fire risk.
Appliances fall into three broad categories for ventilation purposes. Heavy-duty grease and smoke producers demand a Type I hood with a fire-rated grease extraction system. Medium-duty cooking that generates steam, heat, and moderate grease also calls for a Type I hood, but with a lower airflow allowance. Light-duty equipment producing only heat and moisture can often use a simpler Type II hood.
- Open-flame charbroilers, griddles, and deep fryers produce the most grease-laden smoke and require a Type I hood with high-velocity capture and UL-listed baffle filters.
- Ranges, woks, and tilt skillets generate intense heat along with grease and steam. A Type I hood with a deeper capture area helps contain the thermal plume.
- Combi ovens and convection ovens release bursts of heat and steam but far less grease. A Type I hood is still standard, though airflow can be calculated at the lower end of the range.
- Pizza ovens and bakery deck ovens produce dry radiant heat with minimal grease. A Type II hood designed for heat and moisture removal is often sufficient.
- Dishwashers, pasta cookers, and steam kettles create mostly steam. A Type II condensate hood, or a dedicated heat-and-moisture hood, handles this without grease-rated filters.
- Induction cooktops and holding cabinets emit low heat and no grease. They may not require a dedicated hood at all, depending on local code and the volume of units in one area.
How do I calculate the required exhaust airflow?
You size the exhaust fan using one of two accepted methods. The simpler approach multiplies the hood length by a standard capture velocity, typically 200 to 400 CFM per linear foot for wall-mounted canopy hoods. A 10-foot hood over medium-duty equipment therefore needs 2,000 to 4,000 CFM.
The more precise method assigns a CFM requirement to each appliance based on its duty rating and surface temperature. Gas charbroilers and solid-fuel equipment demand the most airflow, often 400 to 600 CFM per linear foot, while electric fryers and ranges fall into the 200 to 300 CFM range. You add the individual appliance loads to get the total exhaust volume.
For a mixed cooking line under a 12-foot hood, a worked example helps. Suppose you have a gas charbroiler (3 ft at 400 CFM/ft), a gas range (4 ft at 300 CFM/ft), and a deep fryer (3 ft at 250 CFM/ft). The total is (3 × 400) + (4 × 300) + (3 × 250) = 1,200 + 1,200 + 750 = 3,150 CFM. You then compare this figure against the linear-foot method for the same 12-foot hood. At 300 CFM per foot, that gives 3,600 CFM. Most engineers specify the higher of the two numbers, so the fan would be sized at 3,600 CFM minimum.
How do I size the hood to fit the kitchen layout?
The hood must extend at least 6 inches beyond the cooking surface on every open side. If your range is against a wall, you need overhang on the front and both ends. An island installation requires 6 inches of overhang on all four sides. This catches the thermal plume as it spreads outward while rising.
Measure the total width of the equipment line the hood will cover, then add 12 inches minimum to that figure. A 36 inch griddle against the wall needs a hood at least 48 inches wide. Depth follows the same rule. A freestanding 30 inch deep charbroiler calls for a hood at least 42 inches deep. Standard canopy depths run 48 to 54 inches for heavy cooking lines.
Mounting height above the cooking surface typically ranges from 72 to 78 inches to the bottom lip of the hood. Lower placement captures effluent more effectively. Higher placement keeps the hood out of the chef's line of sight. The right balance depends on your tallest piece of equipment and the space available under ceiling obstructions like beams or ductwork.
What filter type works best for my menu?
The filter inside the hood captures grease before it coats the ductwork. Your choice affects fire risk, how often you clean and the fan power needed. Three types dominate commercial kitchens, each suited to a different workload.
- Baffle filters use staggered stainless steel panels. Grease hits the metal, condenses and drains into a trough. They handle high-volume charbroilers and wok stations well, impose a moderate pressure drop and go straight into a dishwasher.
- High-velocity cartridge filters force the airstream through a tight metal maze. They strip finer particles than baffles do, which helps with wood-fired ovens and smokers, but the pressure drop is higher so the exhaust fan must be sized to match.
- Single-layer mesh filters are common in light-duty hoods. They catch large droplets from fryers and griddles but clog quickly with solid grease, so a busy kitchen ends up cleaning them constantly. Their pressure drop starts low and rises fast as they load.
- A mixed cookline often pairs baffle filters over the heavy section with a separate hood using a different filter type over the bakery or pastry zone, keeping the ductwork cleaner where grease load is low.
Match the filter style to the grease volume your menu produces. A diner with a flat top and fryers can run baffle filters indefinitely with routine dishwasher cycles. A steakhouse with a live-fire grill needs the deeper capture of a cartridge system or a high-efficiency baffle bank to stay ahead of the buildup.
How much makeup air does the kitchen need?
Every cubic foot of air the exhaust hood removes must be replaced, or the kitchen goes into negative pressure. Negative pressure fights the exhaust fan, cuts its effective CFM, and pulls in unfiltered outdoor air through door gaps, bringing dust, humidity, and pests. A slight negative pressure keeps cooking odors from drifting into the dining room, but too much makes doors hard to open and can backdraft flue gases from gas appliances.
A safe working rule: supply about 80 to 90 percent of the total exhaust volume as conditioned makeup air. The remaining 10 to 20 percent comes from transfer air, the air that naturally moves from the dining room into the kitchen through pass-through windows or under doors. If you exhaust 4,000 CFM, plan for roughly 3,200 to 3,600 CFM of dedicated makeup air delivered directly to the hood or the immediate cooking zone.
Where you introduce that air matters as much as how much you supply. A short-circuit hood with an integrated makeup air plenum works best. It discharges outside the capture area, so fresh air does not blow across the cooking plume and disrupt capture. If the hood lacks an integrated plenum, ceiling diffusers placed at least six feet from the hood face can work, but avoid placing them directly above the cooking line. In cold climates, heat makeup air to at least 50°F before it reaches the hood. This prevents grease from congealing in the ductwork.
- Size makeup air units for 80 to 90 percent of total exhaust CFM.
- Deliver air through the hood plenum or diffusers placed away from the capture zone.
- Heat incoming air to a minimum of 50°F in cold seasons to avoid duct blockages.
- Balance the system so kitchen pressure is slightly negative relative to the dining room.
- Interlock the makeup air fan with the exhaust fan so one cannot run without the other.
What fire safety and code requirements apply?
Your hood classification depends on what is underneath it. You must install a Type I hood over any equipment that produces grease-laden vapors: charbroilers, fryers, woks, griddles and solid-fuel appliances. Type II hoods handle heat, steam and odors only, making them suitable above dishwashers, pasta cookers and ovens without exposed flames.
You cannot compromise on clearance to combustible materials. NFPA 96 requires an 18-inch minimum gap between the hood and any uninsulated combustible surface. For single wall duct passing through a combustible wall or roof, that clearance jumps to 18 inches as well. If the duct is insulated to the standard specified in the code, you can reduce the gap to 3 inches.
Automatic fire suppression turns a hood from a passive canopy into an active safety system. The trigger is a fusible link rated at 360°F or higher, installed in the capture area directly over each cooking appliance. When that link melts, the suppression system discharges wet chemical agent through nozzles aimed at the cooking surface, the plenum and the exhaust duct. The same action must simultaneously cut off the gas or electric supply to all equipment under the hood. This means your gas valve or shunt trip breaker must be wired into the suppression control panel and tested at installation.
FAQ
Can I use a residential range hood in a small restaurant kitchen?
No. Residential hoods lack the fire-rated construction, listed grease filters and capture area required by commercial codes. An inspector will flag it immediately, and your fire insurance may be void.
What happens if the hood is too small for the cooking line?
Smoke and grease escape into the kitchen, which means poor air quality, greasy walls and a higher fire risk. The exhaust fan also works harder, raising energy costs without solving the capture problem.
Do I need a Type I or Type II hood?
Type I hoods are for equipment that produces grease and smoke, such as fryers, griddles and charbroilers. Type II hoods handle heat, steam and odors only, so they suit dishwashers, ovens and steamers. Most hot cooking lines require a Type I hood.
