Range Hood CFM Calculator

The three sizing rules

By width. The Home Ventilating Institute (HVI), which certifies fan ratings, recommends 100 CFM per linear foot of range for a hood against a wall and 150 over an island, where there is no wall to hold the rising air in. Its minimums are 40 and 50 CFM a foot.

By the burners, for gas. Today's Homeowner adds up the BTU rating of every burner and divides by 100: 40,000 BTU needs 400 CFM. If you do not know the ratings it suggests assuming 10,000 BTU a burner, and erring high for a professional-style range. HVI itself says to follow the cooktop maker's advice for professional-style ranges, so check the manual of a big range first.

By the room, if you want it. Today's Homeowner also sizes a hood to change the kitchen's air 15 times an hour: length times width times ceiling height, divided by 4. A 16 by 16 ft kitchen with an 8 ft ceiling gives 512 CFM. That rule is not HVI's and it pushes most kitchens over 400 CFM, so the calculator leaves it off unless you tick it, for an open-plan room or heavy cooking.

The calculator takes the highest of the rules you use and then adds Today's Homeowner's allowance for the duct: 1 CFM a foot of duct, 25 for each elbow and 40 for a roof cap. Its own worked example, a 30-inch gas range of 40,000 BTU in that 16 ft kitchen with 10 ft of duct, two elbows and a roof cap, comes to 612 CFM.

Three kitchens, worked through

The middle kitchen is the common trap: the burner rule lands exactly on 400 and the duct takes it over. A hood rated at 400 CFM or less on a short, straight run keeps you under the line, and the calculator says so when the duct is what tips you over.

The 400 CFM line: makeup air

Section M1503.6 of the International Residential Code, as UpCodes publishes it, says that where a gas, liquid or solid fuel-burning appliance that is neither direct-vent nor mechanically vented is inside the home's air barrier, each exhaust system "capable of exhausting in excess of 400 cubic feet per minute" must be given makeup air at about the rate it exhausts. The makeup air needs at least one outdoor air duct and a damper that opens automatically when the hood runs. Earlier editions of the code, still adopted in some places, set the same 400 CFM line with no condition about the appliances, so a city on an older code can require makeup air for any big hood. Your building department will tell you which edition applies.

The reason is safety. The Department of Energy's Building America Solution Center warns that a very powerful hood "can easily backdraft a non-sealed-combustion furnace, water heater, or fireplace", pulling exhaust gases back into the house. If your water heater or furnace has a metal vent pipe rising into a chimney, it draws room air and counts. A makeup air unit is a real line on the bid: HVACDatabase puts a professionally installed one at $1,500 to $4,500. Range hood permit requirements covers when the city gets involved.

Rated CFM is not delivered CFM

The number on the box is measured in a lab. Duct, elbows and the cap all cut what the hood moves once installed, which is why the Building America guide says ENERGY STAR recommends buying a hood rated 150 to 200 CFM to be sure of the code's 100 CFM minimum for an intermittent kitchen fan. HVI adds that "inflated performance ratings are common" on hoods that are not HVI-Certified, so look for the certification. The same DOE guide says the duct should be rigid metal with a smooth inside, and asks for a back-draft damper and as few bends as possible.

For a hood up to 300 CFM, the calculator checks your run against the code's own duct table (IRC Table M1504.2 on UpCodes), which gives the longest smooth duct of each diameter and takes 15 ft off for every elbow. The table is strict: at 300 CFM a 6-inch duct is allowed only 9 ft with no elbows. The code accepts any run that meets the hood maker's design criteria instead, so the installation instructions are the first place to look. The table stops at 300 CFM; above that, the instructions are the rule.

Width, height and noise

Make the hood at least as wide as the cooktop: the Building America guide says a hood over an open-top broiler should cover its full width and depth. HomeAdvisor describes wall-mounted hoods as installed two to three feet above the stovetop; the hood's instructions give the exact range. ASHRAE 62.2, the residential ventilation standard, limits an occupant-controlled kitchen fan to 3 sones, and a hood too loud to run is a hood nobody turns on. A recirculating hood is not a way round any of this: HVI says ductless hoods "provide no actual ventilation".

What all of it costs, line by line, is in range hood installation cost by type and region, range hood ductwork installation cost and island range hood installation cost. Once you have a bid, the quote checker puts it against the published prices, and what a range hood quote should include explains each line. Thinking of doing it yourself? Read can you install a range hood yourself.

Sources, all read on 19 October 2026: Home Ventilating Institute, How much ventilation do I need?; Today's Homeowner, How to calculate range hood fan size; US DOE Building America Solution Center, Kitchen exhaust fans; UpCodes, IRC M1503.6 Makeup air required; UpCodes, IRC M1504.2 and Table M1504.2 Duct length; HomeAdvisor, Range hood installation cost; HVACDatabase, Makeup air unit installation cost. A planning estimate, not a design: the hood's instructions and your local code decide.