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The code whose kitchen extract and make-up air rules the page restates.
Each opens on its own market's rules. The IRC adds make-up air for big hoods in homes with naturally drafting appliances; Canada's code asks it for any exhaust fan in a home with naturally vented heating; England's guidance has no make-up air figure and instead limits a kitchen fan beside an open-flued appliance. Jurisdictions adopt different editions and amend them, so the code in force where you build governs.
The width of the cooking surface the hood serves, which sets the trade guide's airflow.
Measure the hob or range itself. HVI's guide works per linear foot of range, so a 30 in (76 cm) range is 2.5 ft and a 36 in (91 cm) range 3 ft. A hood is usually at least as wide as the cooktop; England's ventilation guidance asks that a cooker hood span at least the full width of the cooker.
Tools needed: Tape measure
A hood over an island has no wall behind it to steer the plume, so the guide asks more of it.
HVI's recommended figure for an island hood is half as much again as for a wall hood, and its minimum a quarter more. The codes' minimums do not change with position.
The most the hood is rated to move, from its label or data sheet; the codes judge what it is capable of, not the speed you use.
The IRC's make-up air rule reads 'capable of exhausting', so take the highest-speed rating. US hoods are rated in CFM, European ones usually in m³/h; 100 CFM is 47.2 L/s and 1,000 m³/h is 278 L/s. A rating is measured against a stated static pressure, and a long or tight duct delivers less, but the code threshold is applied to the rating.
Whether a hood running hard could pull flue gases back down a natural-draft flue, which is what the make-up air rules guard against.
A direct-vent or room-sealed appliance takes its air from outside through its own pipe. A natural-draft (open-flued) appliance draws its air from the room and relies on warm flue gas rising, and a strong extract can reverse it. Under the IRC any such fuel-burning appliance inside the air barrier counts, fireplaces and stoves included; Canada's rule names space- and water-heating appliances; England's 20 l/s cap applies to an open-flued gas appliance in the kitchen itself. A power-vented (mechanical-draft) appliance still draws room air, but the IRC and the NBC exempt it, so a US or Canadian reader with only power-vented appliances chooses the first option; in England an appliance that draws its air from the room is open-flued even with a fan, and Part J still reaches it. An unvented gas cooktop or range is none of these: M1503.6's words do not on their face exclude one, while Part J's cap and Canada's article do not concern it, so whether it counts is the code official's decision.
Make-up air the code asks for
600 CFM
The hood's rating is above the 400 CFM (189 L/s) line in M1503.6 of the 2021 IRC, and a natural-draft appliance shares the air barrier, so that section asks for make-up air at about the hood's own rate, mechanical or passive, with a damper that opens when the hood runs. This needs checking by a qualified person before you proceed. This restates a published requirement and compares it with what you entered. It is not an inspection and it is not a compliance determination — a competent person has to verify the installed work.
- Hood airflow as rated
- 600 CFM
- Code minimum for a kitchen extract
- 100 CFM
- HVI's recommended airflow for this cooktop
- 250 CFM
- HVI's minimum for this cooktop
- 100 CFM
- Airflow at which the code's combustion-air rule starts
- 400 CFM
They open the calculator with your figures already in it
Range Hood and Cooker Hood Airflow Calculator (CFM, L/s and Make-Up Air): 600 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)
- International Code Council, 2021 International Residential Code, as adopted without amendment in the Colorado Division of Fire Prevention and Control Residential Code 2021: M1503.6 makeup air for an exhaust system capable of more than 400 cfm (0.19 m³/s) where a fuel-burning appliance that is neither direct-vent nor mechanical-draft is inside the dwelling unit's air barrier, at a rate approximately equal to the exhaust rate, with the space-cooling exception; Table M1505.4.4, kitchens 100 cfm intermittent or 25 cfm continuous (its footnote a states the bathroom rate at 0.25 in. w.c., 62 Pa; the kitchen row names no static pressure); M1505.3, fans listed and labeled for their airflow to ANSI/AMCA 210-ANSI/ASHRAE 51. Ohio's Residential Code (Ohio Adm. Code 4101:8-15-01, effective 1 July 2019) and the 2024 IRC carry the same 1503.6 wording
- National Research Council of Canada, National Building Code of Canada 2020 (NBC 2020), Division B: 9.32.3.7.(1)–(3), a supplemental exhaust fan of not less than 50 L/s in each kitchen and its exceptions; 9.32.3.8, protection against depressurization: with a fuel-fired space- or water-heating appliance that is not direct- or mechanically vented, outdoor makeup air from a fan rated at not less than the exhausting device's capacity and not more than 10% above it, interlocked with it, tempered to at least 12 °C or delivered to an unoccupied area; exceptions for solid fuel only, a CAN/CGSB-51.71 depressurization test, and radon subfloor systems
- HM Government, Approved Document F Volume 1: Dwellings (2021 edition, in force 15 June 2022): Table 1.1, intermittent extract of 30 l/s from a kitchen with a cooker hood extracting to the outside and 60 l/s without one; Table 1.2, a continuous high rate of 13 l/s; paragraph 1.21, a cooker hood 650 to 750 mm above the hob unless the maker specifies; paragraphs 0.17–0.18, fans and open-flued appliances under Approved Document J
- HM Government, Approved Document J (2010 edition incorporating 2010, 2013 and 2022 amendments), 1.20: where a kitchen contains an open-flued gas appliance, the kitchen extract fan's rate should not exceed 20 litres/second (72 m³/hour); 40 l/s for an oil appliance with a pressure-jet burner and 20 l/s with a vaporising burner; no extract in the same room as a solid fuel appliance; 1.21, a spillage test under the greatest depressurization
- Home Ventilating Institute, 'How Much Ventilation Do I Need?' (Home Ventilation Guide): range hoods against a wall 100 CFM recommended and 40 CFM minimum per linear foot of range; over an island 150 and 50; worked at 2.5 ft, 3 ft and 4 ft
Inputs used
- Code
- United States: 2021 IRC (M1503.6, M1505.4.4)
- Cooktop or Range Width
- 30 in
- Hood Position
- Against a wall
- Hood's Rated Airflow at Its Top Setting
- 600 CFM
- Fuel-Burning Appliances in the Home
- A natural-draft (open-flued) furnace, boiler or water heater elsewhere in the home
Intermediate steps
- Hood airflow as rated
- 600 CFM
- Code minimum for a kitchen extract
- 100 CFM
- HVI's recommended airflow for this cooktop
- 250 CFM
- HVI's minimum for this cooktop
- 100 CFM
- Airflow at which the code's combustion-air rule starts
- 400 CFM
Confidence note: The hood's rating is above the 400 CFM (189 L/s) line in M1503.6 of the 2021 IRC, and a natural-draft appliance shares the air barrier, so that section asks for make-up air at about the hood's own rate, mechanical or passive, with a damper that opens when the hood runs. This needs checking by a qualified person before you proceed. This restates a published requirement and compares it with what you entered. It is not an inspection and it is not a compliance determination — a competent person has to verify the installed work.
What this calculation does not cover
- The codes are restated, not applied. Which edition a jurisdiction adopted, its amendments, and the exceptions each rule carries (the IRC's for space cooling, Canada's for a depressurization test, England's for a specification beyond its guidance) decide what is actually required, and an inspector or building control body decides whether it is met.
- Ratings are not delivered airflow. A hood rated at a stated static pressure moves less through a long, narrow or bent duct. The IRC asks for fans listed and labeled for their airflow and states its bathroom rate at 0.25 in. w.c. (62 Pa), but names no pressure for the kitchen rate; a recirculating hood, which filters and returns the air, extracts nothing and is not a kitchen extract under England's guidance.
- HVI's figures are a trade association's guide per foot of range, not a code; a high-output gas range or a commercial-style cooktop may call for more, and the hood's capture (its depth, its height above the cooktop and whether it overhangs the front burners) matters as much as its airflow.
- No duct, damper or make-up air path is sized. Where make-up air is required, where it enters, how it is tempered and how its damper is controlled are the designer's, and the codes' own subsections say more than the headline figure.
- Combustion safety is a property of the house, not of the hood. Even with no make-up air required on paper, a tight house with a natural-draft appliance can be depressurized by several fans at once, and a worst-case depressurization or spillage test is how that is found out.
Add the equipment this sizes
This result is a specification — 600 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 2026-10-05 · v1.0.0
Regulatory standards & verification citations5
- International Code Council, 2021 International Residential Code, as adopted without amendment in the Colorado Division of Fire Prevention and Control Residential Code 2021: M1503.6 makeup air for an exhaust system capable of more than 400 cfm (0.19 m³/s) where a fuel-burning appliance that is neither direct-vent nor mechanical-draft is inside the dwelling unit's air barrier, at a rate approximately equal to the exhaust rate, with the space-cooling exception; Table M1505.4.4, kitchens 100 cfm intermittent or 25 cfm continuous (its footnote a states the bathroom rate at 0.25 in. w.c., 62 Pa; the kitchen row names no static pressure); M1505.3, fans listed and labeled for their airflow to ANSI/AMCA 210-ANSI/ASHRAE 51. Ohio's Residential Code (Ohio Adm. Code 4101:8-15-01, effective 1 July 2019) and the 2024 IRC carry the same 1503.6 wording
- National Research Council of Canada, National Building Code of Canada 2020 (NBC 2020), Division B: 9.32.3.7.(1)–(3), a supplemental exhaust fan of not less than 50 L/s in each kitchen and its exceptions; 9.32.3.8, protection against depressurization: with a fuel-fired space- or water-heating appliance that is not direct- or mechanically vented, outdoor makeup air from a fan rated at not less than the exhausting device's capacity and not more than 10% above it, interlocked with it, tempered to at least 12 °C or delivered to an unoccupied area; exceptions for solid fuel only, a CAN/CGSB-51.71 depressurization test, and radon subfloor systems
- HM Government, Approved Document F Volume 1: Dwellings (2021 edition, in force 15 June 2022): Table 1.1, intermittent extract of 30 l/s from a kitchen with a cooker hood extracting to the outside and 60 l/s without one; Table 1.2, a continuous high rate of 13 l/s; paragraph 1.21, a cooker hood 650 to 750 mm above the hob unless the maker specifies; paragraphs 0.17–0.18, fans and open-flued appliances under Approved Document J
- HM Government, Approved Document J (2010 edition incorporating 2010, 2013 and 2022 amendments), 1.20: where a kitchen contains an open-flued gas appliance, the kitchen extract fan's rate should not exceed 20 litres/second (72 m³/hour); 40 l/s for an oil appliance with a pressure-jet burner and 20 l/s with a vaporising burner; no extract in the same room as a solid fuel appliance; 1.21, a spillage test under the greatest depressurization
- Home Ventilating Institute, 'How Much Ventilation Do I Need?' (Home Ventilation Guide): range hoods against a wall 100 CFM recommended and 40 CFM minimum per linear foot of range; over an island 150 and 50; worked at 2.5 ft, 3 ft and 4 ft
Which documents these citations point at
- International Residential Code (United States)One- and two-family dwellings and townhouses up to three storeys — structure, fire safety, energy, plumbing, mechanical and electrical in a single document.
- Approved Documents to the Building Regulations (England) — F, J (United Kingdom)Practical guidance on meeting the Building Regulations, one lettered part per subject — Part A structure, Part B fire, Part K protection from falling, Part L conservation of fuel and power, and the rest.
Standards referenced: ASHRAE 51 (American Society of Heating, Refrigerating and Air-Conditioning Engineers, 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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