Range hood CFM = total gas burner BTU ÷ 100, so a 40,000 BTU gas range needs a 400 CFM hood before the duct, and for an electric range the rule is 100 CFM per foot of hood width on a wall and 150 on an island. Enter the BTU or the width above to get the CFM to shop for, with the duct's losses added.
How the range hood CFM calculator works
There are two ways to size a hood and the calculator offers both.
Gas: CFM = total burner BTU/h ÷ 100
By width: CFM = hood width (ft) × 100 on a wall, × 150 on an island
The BTU rule is the one manufacturers use: Hauslane's guide says to "add up all burner BTU ratings and divide by 100", giving 400 CFM for 40,000 BTU. The width rule is from the Home Ventilating Institute (HVI): wall-mounted hoods 100 CFM per linear foot recommended and 40 minimum, island hoods 150 recommended and 50 minimum. HVI's page does not give a BTU rule, so the two methods come from different sources; when both apply, use the higher.
The calculator then adds the duct, using Hauslane's allowance: 1 CFM per foot of duct, 25 CFM for each elbow and 40 CFM for the exterior cap. It never goes below 100 CFM, the vented range hood minimum in ASHRAE 62.2 (as listed by Energy Code Ace), and rounds up to the next 10 CFM.
Worked examples
- 40,000 BTU gas range, 10 ft duct, 2 elbows: 400 CFM for the burners plus 10 + 50 + 40 = 100 CFM for the duct, so a 500 CFM hood.
- 60,000 BTU cooktop, same duct: 600 + 100 = 700 CFM. 90,000 BTU: 900 + 100 = 1,000 CFM.
- 30 in (2.5 ft) hood on a wall, same duct: 250 recommended + 100 = 350 CFM; at the 100 CFM minimum it is 100 + 100 = 200 CFM.
- 30 in hood over an island: 2.5 × 150 = 375, plus the duct is 475 CFM.
Range hood CFM by width
HVI publishes these wall-mounted figures for common widths.
| Hood width | Recommended | Minimum |
|---|---|---|
| 30 in (2.5 ft) | 250 CFM | 100 CFM |
| 36 in (3 ft) | 300 CFM | 120 CFM |
| 48 in (4 ft) | 400 CFM | 160 CFM |
Add the duct allowance to these. Island hoods multiply by 150 recommended, 50 minimum, because there is no wall to contain the rising air.
Range hood CFM for a gas stove
Gas burners add combustion gases and moisture to the air on top of cooking fumes, which is why the BTU rule exists. Enter the actual burner ratings from the plate or manual, not the catalog size: a pro-style range with high-output burners can reach several hundred CFM on the BTU rule alone. Safety matters here: a gas hood should vent to the outdoors, not back into the room, and a carbon monoxide alarm belongs in the kitchen.
Makeup air
A powerful hood pulls as much air out of the house as it blows out, and that air has to come from somewhere. Hauslane notes that hoods "significantly above 400 CFM" may need makeup air, so the calculator warns once the total passes 400 CFM; the exact threshold is set by your local code. Ask your building department before buying a 900 CFM hood.
Ducts and hood quiet
Most home hoods run between 200 and 600 CFM. A larger hood run at low speed is quieter than a small hood at full speed, which is why the calculator suggests buying above the minimum. The duct should be as short and straight as you can make it, and its diameter matters as much as its length: check it with the duct size calculator. Airflow for the rest of the house is in the CFM calculator and the ductwork calculator, and a bathroom is sized in the bathroom fan CFM calculator.
Before you buy
Check the gas line to the range in the gas pipe size calculator and, if you are renovating the whole room, budget it with the kitchen remodel cost calculator. Find the rest of the ventilation and heating tools in the heating and plumbing calculators hub.