Basement Ventilation CFM Calculator
Fan size for a basement or cellar.
Enter your values
ⓘ Live results
Results
- Required fan
- 563 CFM
- With 20% duct allowance
- 675 CFM
- Air changes per hour
- 5
- Volume
- 6,750 cu ft
- In L/s
- 265
Quick answer
Basements typically need 3-6 air changes per hour, more if there is a workshop, radon risk or damp.
CFM = area x height x ACH / 60
How to use the Basement Ventilation CFM Calculator
- 1Measure the basement area and ceiling height.
- 2Pick the use case that matches how the space is occupied.
- 3Add makeup air by cracking a window or fitting a passive inlet on the far side.
Worked example
Using the values the calculator loads with:
Inputs
- Floor area900 sq ft
- Ceiling height7.5 ft
- UseFinished living (5 ACH)
Results
- Required fan563 CFM
- With 20% duct allowance675 CFM
- Air changes per hour5
- Volume6,750 cu ft
- In L/s265
Frequently asked questions
Exhaust or supply?
Exhaust works for damp and fumes; supply slightly pressurises and keeps radon out better.
Continuous or intermittent?
Continuous at low speed controls humidity far better than short bursts.
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.