Downdraft Vent CFM Calculator
Airflow for a downdraft cooktop ventilator.
Enter your values
Enter the cooktop input in BTU/hr.
Choose one of: Pop-up behind cooktop, Rear-mounted low profile.
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.
- Recommended airflow
- 675 CFM
- Equivalent overhead hood
- 675 CFM
- Makeup air needed
- 608 CFM
- Duct at 1600 FPM
- 8.8 in
Quick answer
Downdraft ventilators typically need 2-3 times the CFM of an equivalent overhead hood because they must pull the plume sideways against its natural rise.
CFM = cooktop BTU/hr / 100 x downdraft multiplier
At a glance
| What it does | Airflow for a downdraft cooktop ventilator. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Cooktop input, Downdraft style |
| Main output | Recommended airflow |
| Formula | CFM = cooktop BTU/hr / 100 x downdraft multiplier |
| Cost | Free — no sign-up, no download |
How to use the Downdraft Vent CFM Calculator
- 1Enter total cooktop burner BTU/hr input.
- 2Choose pop-up (better) or low rear-mounted style (needs more air).
- 3Keep duct runs short and straight since downdraft systems are very sensitive to static pressure.
Inputs explained
- Cooktop input(BTU/hr)
- Enter the cooktop input in BTU/hr.
- Downdraft style
- Choose one of: Pop-up behind cooktop, Rear-mounted low profile.
Worked example
Using the values the calculator loads with:
Inputs
- Cooktop input45000 BTU/hr
- Downdraft stylePop-up behind cooktop
Results
- Recommended airflow675 CFM
- Equivalent overhead hood675 CFM
- Makeup air needed608 CFM
- Duct at 1600 FPM8.8 in
Frequently asked questions
Why do downdrafts underperform?
They fight the natural buoyancy of hot air and steam, so a lot of the plume escapes upward before capture.
Rear burners?
Rear burner plumes travel farther to reach the vent, so capture is weaker — favour front-burner use.
What do I need to enter into the Downdraft Vent CFM Calculator?
Just 2 values: cooktop input, downdraft style. 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 Downdraft Vent CFM Calculator work out the answer?
Downdraft ventilators typically need 2-3 times the CFM of an equivalent overhead hood because they must pull the plume sideways against its natural rise. It applies the formula CFM = cooktop BTU/hr / 100 x downdraft multiplier and shows the working so you can check each step by hand.
Is the Downdraft Vent CFM 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.