Kitchen Exhaust Hood CFM Calculator
Determine exhaust fan CFM airflow, make-up air volume (MUA), and NFPA 96 grease duct velocities based on cooking equipment duty and hood styles.
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How Kitchen Exhaust Hood Ventilation Is Sized
Commercial cooking ventilation is regulated by the International Mechanical Code (IMC Section 507) and NFPA 96. Minimum CFM per linear foot depends on cooking heat load and canopy geometry:
Exhaust CFM = Hood Length (Ft) × Code CFM Rate per Linear Foot
Wall Canopy: Light 200 | Medium 300 | Heavy 400 | Extra-Heavy 550 CFM/ft
Island Canopy: Light 300 | Medium 400 | Heavy 500 | Extra-Heavy 650 CFM/ft
Duct Velocity (FPM) = Exhaust CFM / Duct Area (Sq Ft) [Code Range: 1,500 to 2,500 FPM]
Make-Up Air Balance: Exhausting 3,000 CFM without dedicated Make-Up Air creates intense negative air pressure, causing exterior kitchen doors to slam shut, drawing sewer gas through floor drains, and sucking dining room air-conditioning into the hot kitchen.
Frequently Asked Questions
What is the required duct velocity under NFPA 96 standards?
NFPA 96 stipulates that commercial cooking grease exhaust ducts must maintain an air velocity between 1,500 and 2,500 feet per minute (FPM). Velocities below 1,500 FPM allow aerosolized grease to condense and coat duct walls (severe fire hazard); velocities above 2,500 FPM cause excessive static pressure, noise, and energy consumption.
Why should Make-Up Air be slightly less (80-90%) than the exhaust CFM?
The 10% to 15% difference keeps the commercial kitchen under a slight negative air pressure relative to the dining room. This guarantees cooking fumes, garlic odors, and grease vapors never drift into customer seating areas.
What are the overhang requirements for a commercial Type I exhaust hood?
Under the International Mechanical Code (IMC), a Type I canopy hood must extend at least 6 inches beyond the outer edge of the cooking appliances on all open operating sides (front and sides).