Kitchen Makeup Air Calculator
Makeup air for a large range hood.
Enter your values
Enter the hood exhaust in CFM.
Enter the code threshold in CFM.
Enter the home area in sq ft.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Makeup air for a large range hood. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Hood exhaust, Code threshold, Home area |
| Main output | Makeup air required |
| Formula | makeup CFM ≈ exhaust CFM - 400 |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Hood exhaust(CFM)
- Enter the hood exhaust in CFM.
- Code threshold(CFM)
- Enter the code threshold in CFM.
- Home area(sq ft)
- Enter the home area in sq ft.
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.
What do I need to enter into the Kitchen Makeup Air Calculator?
Just 3 values: hood exhaust, code threshold, home area. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Kitchen Makeup Air Calculator work out the answer?
Most codes require makeup air when a kitchen exhaust exceeds 400 CFM, sized to roughly the exhaust rate. It applies the formula makeup CFM ≈ exhaust CFM - 400 and shows the working so you can check each step by hand.
Is the Kitchen Makeup Air Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.