This calculator helps commercial kitchen owners, restaurant operators, and HVAC contractors determine the minimum required exhaust airflow (CFM) for kitchen hood systems based on cooking equipment type and hood dimensions. Proper ventilation sizing ensures code compliance, fire safety, and optimal air quality while avoiding unnecessary energy costs. Enter your hood measurements and cooking type to get an accurate CFM requirement for your business.
Kitchen Exhaust CFM Calculator
Calculate minimum exhaust airflow for commercial kitchen hoods
Ventilation Requirements
How to Use This Tool
Enter your kitchen hood's width (the linear measurement of the cooking surface it covers) and depth (front-to-back dimension). Select the cooking type that best matches your primary equipment: light duty for steaming/boiling, medium for griddles/ranges, or heavy for woks/charbroilers. Add your duct length and count any 90° elbows—each elbow adds 15 equivalent feet of straight duct. Click Calculate to see your required CFM, face velocity, recommended fan size, and estimated energy cost. Use Reset to clear all fields and start over.
Formula and Logic
This calculator uses the International Mechanical Code (IMC) standard for commercial kitchen ventilation:
- Base CFM = Hood Width (feet) × Multiplier
Multipliers: Light Duty = 100 CFM/linear ft, Medium = 150 CFM/linear ft, Heavy = 200 CFM/linear ft - Duct Adjustment = (Equivalent Duct Length ÷ 100) × 10%
Equivalent Length = Straight Duct (ft) + (Elbows × 15 ft) - Total Required CFM = Base CFM × (1 + Duct Adjustment)
- Face Velocity = Total CFM ÷ (Hood Width × Hood Depth in sq ft)
- Recommended Fan Size = Total CFM × 1.2 (20% safety margin), rounded to next 100 CFM
Practical Notes
Business & Trade Considerations:
- Code Compliance: Most jurisdictions adopt IMC or NFPA 96 standards. Under-ventilation risks health department violations, grease fire hazards, and insurance issues. Always verify local amendments—some cities require 200 CFM/linear ft for all commercial cooking.
- Energy Efficiency & ROI: Each 100 CFM increase adds ~$0.15/month in electricity (24/7 operation). Variable frequency drives (VFDs) can save 30-50% energy during non-peak hours. Consider demand-controlled ventilation (DCV) with CO sensors for further savings.
- Ductwork Costs: Galvanized steel duct costs $3-8/linear ft installed. Each 90° elbow adds $50-150. Keep ducts short, straight, and internally insulated to reduce noise and condensation. Avoid excessive bends that increase static pressure.
- Make-Up Air: Exhausted air must be replaced. In winter, heating make-up air can exceed exhaust fan costs. Consider heat recovery ventilators (HRVs) to reclaim 50-70% of exhaust heat. Balance dampers are required by code.
- Maintenance Budgeting: Grease filters require monthly cleaning ($50-200/service) and annual professional deep cleaning ($300-800). Hood surfaces need quarterly degreasing. Factor these into your operational budget.
Why This Tool Is Useful
For restaurant owners and contractors, proper CFM calculation prevents costly rework. Undersized systems fail health inspections, create uncomfortable dining areas, and accelerate grease accumulation (fire risk). Oversized systems waste energy, increase noise, and may cause excessive makeup air demand that overwhelms HVAC. This calculator provides a code-compliant baseline that balances performance with operational costs. It helps with budgeting equipment purchases, estimating utility expenses, and negotiating with HVAC contractors. For e-commerce sellers of kitchen equipment, it ensures customers select appropriately sized fans, reducing returns and support calls.
Frequently Asked Questions
What if my hood is island-style or has multiple sections?
For island hoods, use the same width measurement (the perimeter facing cooking equipment). For multiple hood sections over separate appliances, calculate each section's CFM separately and sum them. If appliances share a common plenum, use total width of all covered cooking surfaces.
Does hood height above cooking surface affect CFM?
Yes, but indirectly. The IMC standard assumes a 24-36 inch mounting height. Higher installations require higher CFM to maintain capture velocity. Add 10% CFM for every 6 inches above 36 inches. However, optimal capture is achieved at the lowest safe height (typically 24-30 inches for electric, 30-36 for gas).
How do I size the actual fan motor?
After calculating total CFM, select a fan rated for at least that CFM at your total static pressure (duct + filters + elbows). A typical commercial kitchen system has 0.5-1.0 inches water gauge static pressure. Add 20% safety margin to CFM and choose the next standard fan size. Consult fan performance curves—fans lose efficiency at higher static pressures. For long duct runs, consider a higher static pressure fan even if CFM is unchanged.
Additional Guidance
Commissioning & Testing: After installation, a balancer must measure actual CFM with an anemometer or flow hood. Adjust belt tension or VFD settings to meet design CFM ±10%. Document results for health department records.
Fire Suppression: Hood CFM affects fire suppression system design (nozzle placement, piping size). UL 300 systems are sized for specific CFM ranges. Inform your suppression contractor of your calculated CFM.
Utility Incentives: Many utilities offer rebates for high-efficiency fans and VFDs. Check with your commercial utility provider—rebates can cover 20-50% of equipment costs.
Lease vs. Buy: For pop-up restaurants or food trucks, consider exhaust rental companies. They provide code-compliant systems with maintenance included, converting capital expense to operational expense.