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Calculators / Ventilation and power

What size range hood do you need?

Tell us your cooktop and the duct you have. You'll get the CFM, the hood width and the duct size, and if the hood needs makeup air.

These are example numbers. Put in yours.

Your cooktop

Cooktop
BTU

Add up every burner on the spec sheet. A 30 in range runs 40,000 to 60,000.

in

30 in is standard. Pro ranges run 36 to 60 in.

Where it sits

Your duct

Duct you have now

Makeup air

Makeup air system

A damper that opens to bring outside air in when the hood runs.

Gas or oil furnace or water heater that vents up a flue?

A metal pipe out the top into a chimney. Sealed units with plastic vent pipes count as no.

Get this hood

400 CFM, 30 in wide

A 30 in hood at 400 CFM or more, on 6 in round duct.

CFM
400
Hood width
30 in
Duct
6 in round
Makeup air
Not needed
See 30 in range hoods on Amazon

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CFM = 40,000 BTU ÷ 100 = 400, rounded up to 400

width = at least 30 in, so a 30 in hood

duct: up to 400 CFM 6 in, up to 900 CFM 8 in, up to 1,200 CFM 10 in → 6 in round

Mounting height

Over gas, most makers want the hood 30 to 36 in above the burners. Check your install sheet.

Wall or roof cap

Buy a cap with a damper sized to the duct, 6 in. A cheap flapper lets cold air in all winter.

See 6 in vent caps on Amazon

How we work it out

Gas hoods are sized by the burners. Electric and induction are sized by width.

gas: CFM = total burner BTU ÷ 100

electric or induction: CFM = width in ft x 100 (150 on an island)

The hood should be at least as wide as the cooktop. On an island, add 3 in on each side, since there's no wall to steer the smoke.

duct: up to 400 CFM 6 in, up to 900 CFM 8 in, up to 1,200 CFM 10 in

A flat 3¼ x 10 in duct carries about what a 6 in round does. If the duct is too small, the hood gets loud and pulls less.

Over 400 CFM, the IRC wants makeup air when the house has a furnace or water heater that vents up a flue. Without it, the hood can pull exhaust back down that flue. Towns change this rule, so check with yours.

Where the numbers come from

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