Kitchen ventilation fans are sized from the hood capture velocity at the front face, usually 0.25 to 0.5 m/s, combined with the heat and grease load, and the exhaust must be balanced by make-up air equal to 80% to 90% of exhaust to avoid a negative building. A typical commercial canopy hood needs 1,000 to 6,000 m³/h depending on width and cooking type, at a static pressure of 150 to 250 Pa through grease filters. Get capture velocity wrong and grease lands on the ceiling; get make-up air wrong and the dining room goes cold and doors slam.
Step 1: Hood Capture Velocity
Capture velocity is the air speed at the hood face that pulls cooking plumes inward; 0.25 m/s suits light cooking like steaming, while 0.5 m/s suits heavy charbroil and wok stations that throw hot greasy vapour. For a 2 m by 1.2 m hood face area of 2.4 m² at 0.4 m/s, the exhaust is about 3,456 m³/h before filters. Standards such as EN 16282 or local codes often prescribe 0.3 to 0.5 m/s, so design to the higher end for Asian or grill-heavy kitchens where the plume is aggressive and the grease is sticky.
Step 2: Static Pressure Through Grease Filters
Mesh or baffle grease filters add 80 to 200 Pa when clean and can double when loaded with fat, so size the fan for 150 to 250 Pa dirty rather than the clean 100 Pa. A 3,000 m³/h hood at 200 Pa is a job for a centrifugal exhaust fan, often a 4-72 or belt-drive unit placed on the roof away from the heat. Undersizing here means the fan cannot pull the plume once filters load, and the kitchen fills with smell exactly at the dinner rush when cooking is heaviest.
Exhaust vs Make-Up Air
| Parameter | Light cooking | Heavy cooking | Rule of thumb |
|---|---|---|---|
| Capture velocity | 0.25 m/s | 0.5 m/s | Match plume aggression |
| Exhaust rate | 1,000 to 2,500 m³/h | 3,000 to 6,000 m³/h | By hood width and load |
| Static pressure | 120 to 180 Pa | 180 to 250 Pa | Size for dirty filters |
| Make-up air | 80% to 90% of exhaust | 80% to 90% of exhaust | Keep building near neutral |
Make-Up Air and Building Pressure
Exhausting 4,000 m³/h without make-up air pulls 4,000 m³/h of unconditioned air through every gap, chilling the kitchen and starving the fan. Supplying 80% to 90%, or 3,200 to 3,600 m³/h, keeps the building near neutral, lets doors open, and delivers tempered air to the cooks. The make-up air is often delivered through a separate supply fan or an air-handling unit, and in winter it should be heated to 16 to 20 °C so the make-up unit, not the kitchen, carries the heat load.
Selecting the Fan
- Set capture velocity by cooking type: 0.25 m/s light, 0.5 m/s heavy.
- Size exhaust from hood face area times capture velocity, plus 10% margin.
- Rate static pressure for dirty grease filters, usually 150 to 250 Pa.
- Provide make-up air at 80% to 90% of exhaust to hold neutral building pressure.
- Choose a grease-rated centrifugal fan with washable baffle filters and roof or external mount.
Grease, Fire, and Maintenance
Kitchen fans must handle sticky grease, so baffle filters that shed fat into a curb channel beat mesh that clogs, and the wheel should be cleanable, often with a belt-drive motor mounted outside the airstream. Fire code typically wants the fan to keep running on a thermal trip and the duct to be accessible for washing every 1 to 3 months; a clogged filter can raise static from 150 to over 400 Pa and trip the motor. Regular wash keeps the 3,000 to 6,000 m³/h flow and the 80% to 90% make-up balance intact.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
Duct Velocity and Layout
Exhaust duct should run 10 to 14 m/s so grease stays airborne to the arrestor yet friction stays under 100 Pa per 10 m; a 3,000 m³/h flow in a 300 mm duct is about 12 m/s, a sound choice. Long runs above 15 m add 150 to 250 Pa, so size the fan for the total, not the hood alone, and keep the duct short and straight to limit grease build-up at elbows. A cleanable access door every 3 to 4 m lets the wash crew reach every section the code expects.
Heat Load and Make-Up Temperature
A busy kitchen rejects 10 to 30 kW of heat from cooking, so make-up air must temper that load or the space climbs past 24 °C and the staff slow down. Supplying 3,200 m³/h at 18 °C against a 5 °C kitchen in winter needs roughly 20 to 30 kW of heating, often from a gas or electric make-up unit paired with the exhaust fan. Balance the two on one control so when exhaust ramps for a dinner rush, make-up and heat rise together and the building holds neutral pressure without a cold draft at the pass.
Commissioning Checks
At hand-over, walk the hood with a vane anemometer and confirm 0.25 to 0.5 m/s capture across the whole face, not just the centre; edge slack lets grease escape. Verify make-up air equals 80% to 90% of exhaust with a manometer showing near-neutral building pressure, and log the clean static, usually 150 to 250 Pa, as the baseline. Re-measure quarterly, because a filter that drifts from 150 to 400 Pa is the early sign the wash schedule slipped and the motor is about to trip.
Noise and Comfort
A kitchen exhaust fan at 70 to 85 dB sits loud, so mount it on spring isolators and route the discharge away from guest areas to keep the dining room under 55 dB. A 5 to 15 dB silencer on the discharge cuts complaint calls, and soft starts avoid the nightly thump that wakes staff when the Sunday clean-up cycle kicks the fan to full speed.
FAQ
How do I size a kitchen exhaust fan?
Size from hood face area times capture velocity: 0.25 m/s for light cooking, 0.5 m/s for heavy charbroil or wok. A 2.4 m² hood at 0.4 m/s needs about 3,456 m³/h before filters. Add 10% margin and rate static for dirty grease filters, usually 150 to 250 Pa, so the fan still pulls the plume when baffles load
Why is make-up air 80 to 90% of exhaust?
Supplying 80% to 90% of exhaust, say 3,200 to 3,600 m³/h for a 4,000 m³/h hood, keeps the building near neutral so doors open and the kitchen stays tempered. At 100% the dining room can go positive and leak smell; below 80% the building goes negative and pulls cold air through cracks.
What static pressure do kitchen hoods need?
Plan 150 to 250 Pa for the dirty condition, because baffle grease filters add 80 to 200 Pa clean and can double when loaded, pushing total past 400 Pa. A 3,000 m³/h hood at 200 Pa suits a centrifugal exhaust fan on the roof. Sizing only for the clean 100 Pa starves the fan exactly when cooking is heaviest.
Can a kitchen fan handle grease safely?
Yes if specified for it: use baffle filters that shed fat into a curb, a cleanable wheel, and a belt-drive motor mounted outside the hot airstream. Fire code wants the fan to keep running on thermal trip and the duct washable every 1 to 3 months.