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The overall length of the hood measured along its front, in the direction the appliances line up.
IMC Table 507.5 rates exhaust airflow per linear foot of hood length, so the full front length of the hood — not the length of the appliances underneath — is what drives the required CFM.
The hood's mounting configuration, which sets its IMC Table 507.5 CFM-per-linear-foot rate.
Island hoods pull air from all sides and so require a higher rate than wall-mounted canopy hoods of the same duty level; eyebrow and backshelf hoods are only rated for lighter-duty appliances.
The duty classification of the heaviest-duty appliance located anywhere under the hood.
When a hood covers mixed-duty appliances, code requires using the rate for the heaviest-duty appliance under the entire hood length, not an average or per-section rate.
Minimum required exhaust airflow (CFM)
2,400 CFM
This is the IMC Table 507.5 code-minimum rate for UNLISTED, field-fabricated Type I hoods. A listed hood tested per UL 710 may qualify for a lower manufacturer-published exhaust rate — check the specific hood's listing and manufacturer data before finalizing exhaust fan selection.
- Hood length
- 8 ft
- CFM per linear foot rate used
- 300 CFM/ft
- Same airflow in L/s
- 1,132.67 L/s
They open the calculator with your figures already in it
Commercial Kitchen Ventilation Hood Exhaust CFM Calculator: 2,400 CFM — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- CFM = hood length (linear ft) x CFM-per-linear-foot rate, selected by hood style and cooking-duty classification, per International Mechanical Code (IMC) Table 507.5 (the code-minimum method for unlisted/field-fabricated Type I hoods; NFPA 96 references the same duty classifications). Listed hoods tested per UL 710 may use lower manufacturer-published rates instead — this table is the code-minimum for unlisted hood construction. When a hood covers mixed-duty appliances, code requires using the rate for the heaviest-duty appliance under the entire hood length.
Inputs used
- Hood Length
- 8 ft
- Hood Style
- Wall-Mounted Canopy
- Cooking Duty Classification (Heaviest Appliance Under Hood)
- Medium Duty
Intermediate steps
- Hood length
- 8 ft
- CFM per linear foot rate used
- 300 CFM/ft
- Same airflow in L/s
- 1,132.67 L/s
Confidence note: This is the IMC Table 507.5 code-minimum rate for UNLISTED, field-fabricated Type I hoods. A listed hood tested per UL 710 may qualify for a lower manufacturer-published exhaust rate — check the specific hood's listing and manufacturer data before finalizing exhaust fan selection.
What this calculation does not cover
- Every CFM exhausted has to come back in, and none of that is in this number. Code requires makeup air for a commercial hood, tempered in a cold climate, and without it the kitchen goes negative: doors drag, gas appliances backdraft, and the hood loses capture at exactly the edge its rate was set on. The makeup air unit is frequently the larger half of the mechanical package.
- The rate assumes a hood physically positioned to catch the plume. Table 507.5's CFM per linear foot is written for a canopy that overhangs the cooking surface on every open side and hangs at the listed height above it. A canopy cut back flush with the appliance line, or hung high to clear a head, spills grease-laden vapour into the room at the full code airflow.
- Extra-heavy duty means solid fuel, and solid-fuel appliances are generally required to have their OWN hood and their own duct, separate from everything else on the line. Selecting that duty level here to cover a wood-fired oven or a charcoal grill returns an airflow for a hood the code will not let it share, and brings spark arrestors and its own grease removal with it.
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This result is a specification — 2,400 CFM — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- CFM = hood length (linear ft) x CFM-per-linear-foot rate, selected by hood style and cooking-duty classification, per International Mechanical Code (IMC) Table 507.5 (the code-minimum method for unlisted/field-fabricated Type I hoods; NFPA 96 references the same duty classifications). Listed hoods tested per UL 710 may use lower manufacturer-published rates instead — this table is the code-minimum for unlisted hood construction. When a hood covers mixed-duty appliances, code requires using the rate for the heaviest-duty appliance under the entire hood length.
Which documents these citations point at
- International Mechanical Code (United States)Mechanical systems other than fuel gas — ventilation, exhaust, ducts and equipment.
Standards referenced: NFPA 96 (National Fire Protection Association, United States); UL 710 (UL Solutions, United States).
A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.
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