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Calculator · Kitchen hood
Commercial kitchen hood CFM calculator
Size a Type I hood to the heaviest cooking appliance under it. The code gives a minimum airflow in CFM per linear foot of hood for each hood style and duty, and the exhaust is that rate times the hood length. A 10 ft wall-mounted canopy over medium duty appliances is 300 x 10 = 3,000 CFM, and one broiler under it lifts the same hood to 4,000 CFM. Listed hoods use the rate on the label. For a kitchen in a house, use the range hood CFM calculator. For the duct runs, use the duct sizing calculator.
- Choose a wall-mounted canopy, a single or double island canopy, an eyebrow or a backshelf hood. For a double island canopy the length is that of each side.
- The tables size the whole hood to the heaviest cooking duty of any appliance under it. Solid fuel is extra heavy, broilers and woks are heavy, griddles and fryers are medium, and ovens and steamers are light.
- The result is the table rate in CFM per foot times the hood length, with the makeup air and the grease duct area. For a listed hood, enter the rate from its label.
Example result for the default inputs
wall-mounted canopy, medium duty, 10 ft.
Minimum exhaust
3,000 CFM
Rate
300 CFM per ft
Source
Unlisted hood table
Makeup air
3,000 CFM
| Hood | wall-mounted canopy, 10 ft |
|---|---|
| Heaviest appliance duty | medium |
| Rate used | 300 CFM per ft, from the unlisted hood table |
| Minimum exhaust | 3,000 CFM |
| Makeup air, about equal | 3,000 CFM |
| Grease duct area at 2,500 fpm | 1.20 ft2, the smallest duct for the range |
| Grease duct area at 500 fpm | 6.00 ft2, the largest duct for the range |
| Hood outlets at 12 ft each | 1 |
- These are the minimums for a hood without a listing. A listed hood takes its rate from the manufacturer's label, which can be lower or higher.
- Makeup air should be approximately equal to the exhaust, and interlocked with it. San Bernardino County asks for at least 80 percent of the exhaust as dedicated makeup air for a listed hood and 100 percent for an unlisted one, so check the local rule.
For estimation purposes only. Consult a licensed engineer for final designs.
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How the hood exhaust is calculated
A Type I hood has to pull enough air to capture and contain the grease-laden vapor over the cooking line. The codes set that as a minimum net airflow in CFM per linear foot of hood. Which rate applies depends on the hood style and on the heaviest duty of the appliances under it. This page multiplies that rate by the hood length, and shows the makeup air and the grease duct area that go with it. The tables are for hoods without a listing. A listed hood takes its rate from its label, and the page accepts that rate in place of the table. Type II hoods and residential range hoods are out of scope.
- Rate
CFM per ft = table value for the hood style and the heaviest dutyFour duty classes and five hood styles give 20 cells, and 3 of them read not permitted. A wall-mounted canopy over medium duty appliances is 300 CFM per foot. Over the same appliances a single island canopy is 500, because it has no wall behind it to steer the plume.- Exhaust
exhaust CFM = CFM per ft x hood length in ftThe default case is 300 x 10 = 3,000 CFM, and results round up to the next whole CFM, so a length such as 10.37 ft never lands under the table. San Bernardino County prints the same formula as "Exhaust CFM = Airflow (CFM per linear foot of hood) x Length of Hood".- Mixed duty
rate = the highest rate of any appliance under the hoodBoth the California tables and the Snohomish County worksheet size the whole hood to the heaviest appliance. A griddle line with one under-fired broiler at the end is heavy duty for its full length. The default hood then needs 4,000 CFM, not 3,000.- Double island
total CFM = 2 x rate x length of one sideThe table rate for a double island canopy is per side. A hood with 8 ft on each side over heavy duty appliances needs 3,200 CFM per side at 400 CFM per foot, or 6,400 CFM for the hood. Sides of different length are run one at a time.- Listed hood
rate = listed CFM per ft from the hood labelA listed hood takes its rate from the manufacturer's listing, and San Bernardino County tells applicants to refer to the manufacturer's specification sheet for it. Enter that rate and the page uses it, with the table shown for comparison. A listing of 250 CFM per foot on the default hood gives 2,500 CFM against 3,000 from the table.- Makeup air
makeup air = exhaust, approximately equalThe Snohomish County worksheet quotes IMC 508, which has makeup air from all sources approximately equal to the exhaust air. That puts the default hood at about 3,000 CFM. San Bernardino County sets its own share. For a listed hood it is 80 percent of the listed exhaust, dedicated, and for an unlisted hood it is 100 percent of the exhaust, as on the default hood.- Grease duct area
duct area ft2 = CFM / velocity in fpmSan Bernardino County asks for a duct velocity of 500 to 2,500 fpm. The Snohomish worksheet quotes a minimum of 500 fpm for a Type I hood. At 3,000 CFM the duct area runs from 1.20 ft2 at 2,500 fpm to 6.00 ft2 at 500 fpm.- Hood outlets
outlets = hood length / 12 ft, rounded upThe Snohomish worksheet says a hood outlet serves not more than a 12 ft section of hood. A 24 ft hood needs at least 2 outlets, and a 100 ft run needs 9.
Rate table and worked examples
The table below is the minimum net airflow in CFM per linear foot for hoods without a listing. It has 20 cells and 3 of them read not permitted. The values are the California Mechanical Code tables as San Bernardino County prints them, the 2012 IMC column on the Snohomish County worksheet and the 2024 IMC table in a study guide. The California reprint leaves out the heavy duty wall-mounted cell, so 400 comes from the other two. Read across a row.
| Hood style | Light | Medium | Heavy | Extra heavy |
|---|---|---|---|---|
| Wall-mounted canopy | 200 | 300 | 400 | 550 |
| Single island canopy | 400 | 500 | 600 | 700 |
| Double island canopy, per side | 250 | 300 | 400 | 550 |
| Eyebrow | 250 | 250 | Not permitted | Not permitted |
| Backshelf or pass-over | 250 | 300 | 400 | Not permitted |
Eight cases run through the same function the form uses. Four share the 10 ft wall-mounted canopy and change only the duty, from 2,000 CFM over light duty to 5,500 CFM over solid fuel. Island cases show the higher island rates and the per-side rule. An eyebrow over a broiler is refused. Last comes an assumed listed rate of 250 CFM per foot, which gives 2,500 CFM against 3,000 from the table.
| Case | Setup | Result |
|---|---|---|
| Default, wall canopy over medium duty | wall-mounted canopy, medium duty, 10 ft | 300 CFM per ft, 3,000 CFM of exhaust, about 3,000 CFM of makeup air |
| Same hood over light duty | wall-mounted canopy, light duty, 10 ft | 200 CFM per ft, 2,000 CFM of exhaust, about 2,000 CFM of makeup air |
| Same hood over heavy duty | wall-mounted canopy, heavy duty, 10 ft | 400 CFM per ft, 4,000 CFM of exhaust, about 4,000 CFM of makeup air |
| Same hood over solid fuel | wall-mounted canopy, extra heavy duty, 10 ft | 550 CFM per ft, 5,500 CFM of exhaust, about 5,500 CFM of makeup air |
| Single island canopy, medium duty | single island canopy, medium duty, 10 ft | 500 CFM per ft, 5,000 CFM of exhaust, about 5,000 CFM of makeup air |
| Double island canopy, heavy duty | double island canopy, heavy duty, 8 ft each side | 400 CFM per ft per side, 6,400 CFM of exhaust for both sides, about 6,400 CFM of makeup air |
| Eyebrow over a broiler | eyebrow, heavy duty, 6 ft | Not permitted in the unlisted hood table |
| Default hood with an assumed listing | wall-mounted canopy, medium duty, 10 ft, listed at 250 CFM per ft | 250 CFM per ft, 2,500 CFM of exhaust, about 2,500 CFM of makeup air |
Standards and data sources
- California Mechanical Code tables 508.10.1.2 to 508.10.1.5, San Bernardino County Environmental Health Services data sheet (revised April 2022) - The minimum net airflow in CFM per linear foot for hoods without a listing, by hood style and duty class, with the sentence "Hoods shall be sized to the highest (heaviest) duty level of the appliances installed underneath the hood". It lists the appliances in each duty class, a duct velocity of 500 to 2,500 fpm and the county's makeup air shares. The reprint leaves out the heavy duty wall-mounted row. Tests reproduce its printed cells.
- Snohomish County (WA) Planning and Development Services, Commercial Kitchen Hood Worksheet (revised October 8, 2013, 2012 IMC) - The unlisted hood table of the 2012 IMC at 507.13.1 as 550, 400, 300 and 200 CFM per lineal foot, the rule that the highest rate applies to the entire hood, makeup air approximately equal to exhaust under 508, a 500 fpm minimum duct velocity under 506.3.4 and a 12 ft section per hood outlet. It supplies the heavy duty wall-mounted 400 that the California reprint omits. Section numbers changed in later IMC editions.
- Open Exam Prep, ICC commercial mechanical study guide, Type II hoods, filters and kitchen exhaust rates (2024 IMC) - A secondary source for the full 20 cell table as the 2024 IMC prints it, with a heavy duty wall-mounted canopy at 400 CFM per foot. It repeats the rule that the heaviest appliance sets the rate for the entire hood and that solid fuel appliances take an independent hood. Tests compare the table with it cell by cell.
Limitations of this calculator
- The table is for hoods without a listing. A listed hood takes its rate from the manufacturer's label, which can be below or above the table. That is why the optional field takes that rate, from 50 to 1,500 CFM per foot, and the table is shown for comparison. Leave it blank otherwise.
- The tables are the California Mechanical Code values, the 2012 IMC values on the Snohomish County worksheet and the 2024 IMC values in a study guide. Section numbers changed between IMC editions, and states, counties and cities amend them. The edition and amendments your authority having jurisdiction adopted decide the number. Verify before you quote it.
- The California reprint omits the heavy duty wall-mounted row. This page uses 400 CFM per foot there, which the Snohomish worksheet and the study guide both give. No primary code text was read for that cell.
- Type I hoods only. A Type II hood over steam, heat or dishwashing is not computed. One study guide quotes 100 CFM per foot for a Type II dishwashing hood under the 2024 IMC, but no primary text confirmed it, so the page leaves it out.
- Mixed duty is sized to the heaviest appliance for the whole hood. Solid fuel appliances need their own exhaust system on the Snohomish worksheet, so do not put them under a shared hood. Keep them apart.
- The result is the minimum exhaust only. It does not size the exhaust fan, the static pressure of the filters and duct, the grease filters or the capture performance. The grease duct rows give an area range at 500 to 2,500 fpm and nothing more about the duct.
- Makeup air is shown as approximately equal to the exhaust. Local rules differ. San Bernardino County asks for 80 percent for a listed hood and 100 percent for an unlisted one, dedicated, and interlocked with the exhaust. Many jurisdictions also limit how cold the supplied air can be. Ask the inspector.
- NFPA 96, the fire code and the fire suppression system are outside this page. Grease duct construction, clearances, enclosures, access panels and the shutdown of appliances and makeup air when the suppression system trips come from those documents and the local fire official.
- Appliance lists for the duty classes come from the California Mechanical Code as the San Bernardino County sheet prints it. The IMC defines the duty classes in its own text, and the two differ in places. That worksheet puts a gas burner range in heavy duty, where California lists gas open-burner ranges as medium. This page files a gas open-burner range under heavy, the higher rate. Check the class of each appliance against the code your jurisdiction adopted.
- This is a planning estimate, not a hood design. A licensed engineer, the hood manufacturer's data and the authority having jurisdiction decide the installed airflow. For a kitchen in a house, use the range hood CFM calculator.
Common kitchen hood sizing mistakes
- Sizing to the typical appliance. The tables size the whole hood to the heaviest appliance under it. A 10 ft wall canopy over a griddle line needs 3,000 CFM. Add one under-fired broiler and the same hood needs 4,000 CFM, which is 1,000 CFM more. The heaviest one wins.
- Using the wall rate for an island hood. A single island canopy has no wall behind it, so the rate is higher. Over medium duty appliances it is 500 CFM per foot against 300 for a wall canopy. At 10 ft that is 5,000 CFM, and the wall rate would leave the hood 2,000 CFM short. Islands need more.
- Putting an eyebrow hood over a broiler. The unlisted table does not permit an eyebrow hood over heavy or extra heavy duty appliances. It does not permit a backshelf or pass-over hood over solid fuel either. 3 of the 20 cells read not permitted, and the page refuses those cases. That is deliberate. A listing that covers the appliance is the only way past the table.
- Taking the hood length from the appliance line. The tables multiply by the length of the hood. Per the Snohomish worksheet, canopy hoods shall extend a minimum of 6 inches beyond the cooking surface, so the hood is longer than the cooking line. Measure the hood, not the equipment.
- Applying the table to a listed hood. A listed hood takes its rate from the label. At 250 CFM per foot a 10 ft wall canopy needs 2,500 CFM, which is 500 CFM under the table. A rate printed above the table is the one to build to. Size the fan and the makeup air to the label.
- Leaving makeup air as an afterthought. Exhaust of 3,000 CFM pulls 3,000 CFM of air from somewhere. IMC 508 has makeup air approximately equal to exhaust. San Bernardino County also says the building's HVAC may not be the sole source of makeup air, and wants the makeup air and the hood exhaust interlocked on one switch. Plan both together.
Common questions about kitchen hood CFM
How do you calculate CFM for a commercial kitchen hood?
Multiply the table rate in CFM per linear foot by the hood length in feet. The rate depends on the hood style and on the heaviest duty of the appliances under the hood. A 10 ft wall-mounted canopy over medium duty appliances is 300 x 10 = 3,000 CFM. Listed hoods take the rate from the manufacturer's listing.
What CFM per foot does a wall-mounted canopy hood need?
Over light duty appliances 200 CFM per foot, over medium duty 300, over heavy duty 400 and over solid fuel 550. On a 10 ft hood those are 2,000, 3,000, 4,000 and 5,500 CFM. These are the unlisted hood minimums. Medium is the default.
Which appliances are heavy, medium and light duty?
Heavy duty is under-fired and chain broilers, wok ranges, upright broilers and, on the 2012 IMC worksheet from Snohomish County, gas burner ranges. Medium duty is hot-top ranges, griddles, fryers and conveyor pizza ovens. Light duty is ovens, steamers, pasta cookers, kettles under 20 gallons, cheesemelters and similar. Solid fuel such as charcoal, wood and mesquite is extra heavy. These lists come from the California Mechanical Code as the San Bernardino County data sheet prints it, which puts gas open-burner ranges in medium duty. The IMC defines the duty classes in its own text, and the two differ in places. Check the class of each appliance against the code your jurisdiction adopted.
What if different appliances sit under one hood?
The highest rate applies to the entire hood. Both the California tables and the Snohomish County worksheet say so. A 10 ft wall canopy over griddles and one broiler is sized as heavy duty, 4,000 CFM. Solid fuel appliances are the exception, since they need their own exhaust system.
What is the CFM rate for an island hood?
A single island canopy over medium duty appliances is 500 CFM per foot, which is 5,000 CFM at 10 ft. Double island canopies take the rate per side. Heavy duty at 400 CFM per foot on 8 ft sides is 3,200 CFM per side and 6,400 CFM in all. Run each side alone when they differ.
Is an eyebrow hood allowed over a broiler?
Not in the unlisted table. An eyebrow hood is not permitted over heavy or extra heavy duty appliances, and a backshelf or pass-over hood is not permitted over solid fuel appliances. A listed hood can be accepted when its listing covers the appliance, so check the label and the manufacturer's data.
How is a listed hood different from an unlisted one?
A listed hood has been tested, and its label or specification sheet gives the exhaust rate to use, while the table applies only to hoods without a listing and a listed hood is sized to its label. If that label says 250 CFM per foot, a 10 ft hood needs 2,500 CFM. The calculator shows the table figure next to it, 3,000 CFM, for comparison.
How much makeup air does a kitchen hood need?
The Snohomish County worksheet quotes IMC 508, which has makeup air from all sources approximately equal to the exhaust. For 3,000 CFM of exhaust that is about 3,000 CFM. San Bernardino County asks for 80 percent as dedicated makeup air for a listed hood and 100 percent for an unlisted one. Local rules vary.
What size grease duct does the exhaust need?
San Bernardino County asks for a duct velocity of 500 to 2,500 fpm, and the Snohomish worksheet quotes a 500 fpm minimum for a Type I hood. For 3,000 CFM that is a duct area from 1.20 ft2 to 6.00 ft2. Pick inside that range. Duct construction and clearances follow NFPA 96 and the local code.
Does this cover a Type II hood or a home range hood?
No. This page is for Type I hoods over grease-producing cooking. Type II hoods over steam and heat are not computed. A kitchen in a dwelling uses the residential range hood calculator, which works from HVI and the IRC.
Is there a limit on how many times I can run this?
No. This calculator runs in your browser with no daily limit and no signup.
Used on the same job
Size the exhaust, then the system around it
The exhaust CFM is the minimum for the hood. The fan also has to overcome the static pressure of the filters and the grease duct, which the static pressure calculator helps with, and the duct size comes from the duct velocity and friction calculator. Makeup air, fire suppression and the grease duct enclosure follow the local code and NFPA 96. You can also ask the assistant to go over a kitchen exhaust layout.
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