Downdraft Vent CFM Calculator
Airflow for a downdraft cooktop ventilator.
Enter your values
ⓘ Live results
Results
- 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
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.
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.
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.