Kitchen Hood CFM Calculator: engineer's guide
Kitchen hoods are sized by hood type, cooking appliance duty, and capture velocity at the front edge of the hood.
Open the Kitchen Hood CFM calculator →
What this calculator does
The calculator applies the IMC 507.13 rate for the selected hood type and appliance duty and reports the required exhaust CFM.
Formulas used
- Type I hood CFM/ft:
CFM = L × rateduty - Duty rates (CFM per linear ft):
Light 200, Medium 300, Heavy 400, Extra Heavy 550
Variables
- L = hood length, ft
- rateduty = per-foot CFM based on appliance duty
Worked example
Scenario: 12 ft long Type I wall canopy hood over a heavy-duty grill and fryer combination.
- Heavy duty rate = 400 CFM/ft
- Exhaust CFM = 12 × 400 = 4800 CFM
- Makeup air 80% of exhaust = 3840 CFM tempered outdoor air
- Duct velocity 1500 to 1800 fpm with grease-tight seams
Common mistakes to avoid
- Sizing on room volume (ACH) instead of hood duty
- Ignoring the 80% tempered makeup air requirement
- Missing the fire suppression interlock
- Using flexible duct on a Type I exhaust (not permitted)
Frequently asked questions
Type I vs Type II?
Type I over grease-producing appliances; Type II over dishwashers and steam only.
Ductwork material?
Welded 16 gauge black steel for Type I with fire-rated shaft.
Standards and references
IMC 507, NFPA 96, ASHRAE 154
Related tools on this site
Open the calculator that pairs with this guide: Kitchen Hood CFM Calculator.
Verification note
This guide is planning support only. Final design must be verified against the applicable project specification, authority requirements, manufacturer data, and the standards cited above. Consult a licensed engineer for construction-issue calculations.