Commercial Kitchen Exhaust CFM Calculation
Covers: CFM calculation formulas (heat-based and hood-area-based), hood design, duct sizing, grease filtration, makeup air systems.
The exhaust system is the most technically demanding component of commercial kitchen design. Insufficient airflow allows grease and smoke to accumulate, creating fire hazards and health risks. Excessive airflow wastes energy and creates uncomfortable working conditions. Proper CFM calculation requires consideration of cooking equipment type, hood dimensions, duct layout, and environmental emission standards.
- Two CFM Calculation Methods
- Hood Design & Selection
- Duct System Design
- Grease Filtration Equipment
- Makeup Air Requirements
- FAQ
1. Two CFM Calculation Methods
Use both methods and select the higher value for design. CFM CalculationExhaust Design
Method 1: By Heat Output
CFM = BTU/hr ÷ 100 × factor
| Equipment Type | CFM per 1000 BTU/hr | Notes |
|---|---|---|
| Chinese wok range (high-heat) | 150-200 | Heavy grease, high smoke |
| Western range / griddle | 100-150 | Moderate grease |
| Induction cooktop | 70-100 | No open flame, less smoke |
| Steamer / combi oven | 50-80 | Primarily steam |
| Deep fryer | 150-200 | High-temperature grease |
Method 2: By Hood Area
CFM = Hood Area (sqft) × CFM/sqft factor
| Kitchen Type | Capture Velocity | CFM per sqft |
|---|---|---|
| Chinese/wok kitchen | 2.0-2.5 ft/s | 150-200 CFM/sqft |
| Western kitchen | 1.5-2.0 ft/s | 100-150 CFM/sqft |
| Pastry / steam kitchen | 1.0-1.5 ft/s | 75-100 CFM/sqft |
| Institutional (large batch) | 2.0-3.0 ft/s | 150-250 CFM/sqft |
Calculation Example
Chinese kitchen: 2 double wok ranges (total 140,000 BTU/hr) + 1 fryer (50,000 BTU/hr):
- Method 1: 190,000 ÷ 1000 × 175 = 33,250 CFM (very high - conservative)
- Method 2: Hood 40 sqft × 175 CFM/sqft = 7,000 CFM
- Realistic design value: 7,000-10,000 CFM (use hood-area method as primary, add 10-15% safety margin)
2. Hood Design & Selection
The hood is the entry point of the exhaust system. Hood DesignCanopy Hood
| Parameter | Standard | Notes |
|---|---|---|
| Mounting Height | 6-6.5 ft (1.8-2.0m) above cooking surface | Too high = poor capture; too low = obstructs cooking |
| Overhang (depth) | 6-8in (150-200mm) beyond equipment | Ensures complete smoke capture |
| Width | Match equipment width + 4in each side | Full coverage of cooking zone |
| Material | 304 stainless steel, 18-20 ga | Corrosion resistant, easy to clean |
| Filter Type | Baffle filters / water-wash hood | Water-wash hoods remove 70-80% grease pre-filter |
Recommendation: Chinese/wok kitchens should use water-wash (ventilating) hoods, which remove 70-80% of grease particles via water curtain before the main duct, reducing fire risk and downstream filter load.
3. Duct System Design
Duct sizing, material, and layout directly impact exhaust efficiency and noise. Duct DesignExhaust Engineering
Duct Sizing Formula
Duct Area (sqft) = CFM ÷ Velocity (ft/min)
| Duct Location | Velocity | Noise Limit |
|---|---|---|
| Main horizontal duct | 1,500-2,000 ft/min | ≤65 dB |
| Branch ducts (hood to main) | 1,000-1,500 ft/min | ≤60 dB |
| Vertical riser | 2,000-2,500 ft/min | Stack effect assists |
Duct Material
- Galvanized steel: Economy choice, 22-18 gauge, standard for most kitchens
- Stainless steel: Premium kitchens, high-corrosion environments, longest life
- FRP (fiberglass): Chemical/food processing, acid-resistant
4. Grease Filtration Equipment
Grease filters are critical for fire safety and environmental compliance. Grease FilterEPA Compliance
| Filter Type | Efficiency | Price Range | Application |
|---|---|---|---|
| Electrostatic precipitator | 90-95% | $700-$2,800 | Standard restaurants |
| Composite (ESP + UV) | 95-98% | $2,100-$7,000 | Premium dining, residential areas |
| Carbon filter | 95%+ odor removal | $1,100-$4,200 | Odor-sensitive locations |
| Wet scrubber | 85-90% | $400-$1,400 | Large institutions, pre-treatment |
Important: US EPA and local fire codes regulate kitchen exhaust emissions. Check local requirements for grease removal efficiency and particulate limits before specifying equipment.
5. Makeup Air Requirements
Exhaust without adequate makeup air creates negative pressure, reducing exhaust efficiency and causing doors to slam. Makeup AirVentilation
| Parameter | Standard | Notes |
|---|---|---|
| Makeup Air Volume | 80-90% of exhaust CFM | Maintain -0.02 to -0.04 in. w.g. negative pressure |
| Supply Method | Task ventilation + general supply | Direct supply to cook positions |
| Supply Temperature | Summer: 78-82°F; Winter: 60-65°F | Requires HVAC or heat exchanger |
| Supply Location | Away from hood, avoid disrupting plume | Don't blow directly on cooking equipment |
6. FAQ
About Fengzhida
Fengzhida provides complete commercial kitchen exhaust solutions: 304 stainless steel hoods (baffle or water-wash type), electrostatic precipitators, centrifugal fans, and duct system design. OEM/ODM available. Products certified to CE standards.
Related: Commercial Kitchen Power Requirements | Stainless Steel Fabrication | Commercial Oven Types
Published by Fengzhida Commercial Kitchen Equipment.