Kitchen Makeup Air Calculator
Makeup air for a large range hood.
Enter your values
ⓘ Live results
Results
- Makeup air required
- 500 CFM
- Required?
- Yes — code triggered
- Duct size at 700 FPM
- 11.4 in dia
- Heater load at 40°F rise
- 21,600 BTU/h
- Whole-home exchange
- 7.5x typical ventilation
Quick answer
Most codes require makeup air when a kitchen exhaust exceeds 400 CFM, sized to roughly the exhaust rate.
makeup CFM ≈ exhaust CFM - 400
How to use the Kitchen Makeup Air Calculator
- 1Enter the hood's rated exhaust at the speed you actually cook on.
- 2Check your local threshold — often 400 CFM.
- 3Interlock the makeup air damper with the hood switch and temper the incoming air in cold climates.
Worked example
Using the values the calculator loads with:
Inputs
- Hood exhaust900 CFM
- Code threshold400 CFM
- Home area2400 sq ft
Results
- Makeup air required500 CFM
- Required?Yes — code triggered
- Duct size at 700 FPM11.4 in dia
- Heater load at 40°F rise21,600 BTU/h
- Whole-home exchange7.5x typical ventilation
Frequently asked questions
What happens without makeup air?
The house goes negative, which can backdraft water heaters and fireplaces and pull in radon.
Can I just crack a window?
It helps, but codes usually require a powered, interlocked supply above the threshold.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.