Commercial Kitchen Hood Exhaust (IMC 507)
Commercial-kitchen hood exhaust airflow for Type I (grease) and Type II (vapor) hoods.
Example
You enter
- Hood class I
- Hood type (Type I; Type II light-duty) wall-canopy
- Cooking-appliance duty heavy
- Hood length (ft) 8
- Duct velocity (fpm; default 1500) 1500
You get
- Exhaust airflow Q (cfm) 3200
- Multiplier (cfm/ft of length) 400
- Makeup air (cfm; 80%) 2560
Checked against published worked examples from: ICC.
Details, formula, and sources
ScopeType I (grease) and Type II (vapor-only) commercial-kitchen hood exhaust airflow per IMC 2021 §507.5.1-507.5.4 (Type I) / §507.5.5 (Type II) duty multipliers. Makeup air, duct area, grease-duct slope reminder. NFPA 96 governs grease-handling exhaust system design.
Formula or tableType I: Q = duty_multiplier * L. Wall-canopy duty multipliers (light 200, medium 300, heavy 400, extra-heavy 550 cfm/ft) per IMC 2027 §507.2.10.1-507.2.10.3 (Type I) and §507.3.4.1 (light duty) [§507.5.1-507.5.4 in IMC 2021]. Single-island canopy (400 / 500 / 600 / 700). Double-island (250 / 300 / 400 / 550). Backshelf / proximity / pass-over (250 / 300 / 400; extra-heavy not allowed). Type II: dishwashing Q = 100 * L (IMC 2027 507.3.4.2 [507.5.5 in 2021]); light-duty cooking or food preparation Q = light-duty rate for the hood type * L (IMC 2027 507.3.4.1 [507.5.4 in 2021]). Makeup = 0.80 * Q (IMC 508 balance check). Duct area (in^2) = Q / V * 144.
Source and editionIMC 2027 §507.2.10 (Type I) and §507.3.4 (Type II) [§507.5 in IMC 2021; rates unchanged]. NFPA 96-2024 governs grease-handling exhaust system design.
Free accesscodes.iccsafe.org for IMC TOC; nfpa.org/freeaccess for NFPA 96 TOC.
What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
API field nameshood_class, hood_type, duty, length_ft, duct_velocity_fpm, Q_exhaust_cfm, cfm_per_ft, makeup_cfm
- Hood-type x duty matrix wall-canopy / single-island / double-island / backshelf / proximity / pass-over, each with light / medium / heavy / extra-heavy multipliersIMC 2027 §507.2.10 / 507.3.4.1 [507.5.1-507.5.4 in 2021]
- Type II rate 100 cfm per linear foot over dishwashing appliances; the light-duty rate for the hood type over light-duty cooking or food preparationIMC 2027 §507.3.4.2 / 507.3.4.1 [507.5.5 / 507.5.4 in 2021]
- Makeup air 80% of exhaust as a balance-check rule of thumb; AHJ governs final balanceIMC 2027 §508
- Duct velocity range Type I grease-duct velocity 500-2000 fpm to keep grease suspendedNFPA 96-2024 §8.2.1.1
- Grease-duct slope 1/4 in per ft minimum slope back to the hoodIMC 2027 §506.3.7 (also 2021)