Basement Exhaust Fan Calculator
Mechanical ventilation airflow for a basement.
Enter your values
ⓘ Live results
Results
- Required exhaust
- 67 CFM
- Basement volume
- 8,000 cu ft
- Fan size at 70% duty cycle
- 95 CFM
- Note
- Pair with makeup air path (door undercut or vent) from upstairs
Quick answer
Basements are commonly ventilated at 0.35-1 air changes per hour, more if there is a history of moisture, mustiness or radon.
CFM = volume x ACH / 60
How to use the Basement Exhaust Fan Calculator
- 1Enter basement floor area and ceiling height.
- 2Choose an air-change target — 0.5 ACH is a common baseline, more for damp basements.
- 3Ensure there is a makeup air path so the fan does not starve for air.
Worked example
Using the values the calculator loads with:
Inputs
- Basement area1000 sq ft
- Ceiling height8 ft
- Target air changes0.5 ACH
Results
- Required exhaust67 CFM
- Basement volume8,000 cu ft
- Fan size at 70% duty cycle95 CFM
- NotePair with makeup air path (door undercut or vent) from upstairs
Frequently asked questions
Will this fix moisture problems?
It helps but a dehumidifier is usually still needed to control basement humidity directly.
Where should the fan discharge?
To the exterior, never into an attic or crawlspace, to avoid trapping moisture in the structure.
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.