Crawlspace Exhaust Fan Calculator
Fan airflow for a vented or sealed crawlspace.
Enter your values
ⓘ Live results
Results
- Required airflow
- 24 CFM
- Type
- Conditioned supply air
- Vapor barrier
- Required regardless of type, 6-mil poly minimum
- Dehumidifier alt.
- A crawlspace dehumidifier sized for the volume can substitute for fan ventilation in sealed spaces
Quick answer
Vented crawlspaces needing mechanical assistance are typically fanned at about 1 CFM per 50 sq ft, while sealed crawlspaces instead need a small supply of conditioned air, roughly 1 CFM per 50 sq ft as well.
CFM = area / 50
How to use the Crawlspace Exhaust Fan Calculator
- 1Measure the crawlspace floor area.
- 2Decide whether it is (or will be) vented with fan assist, or sealed/encapsulated.
- 3For sealed crawlspaces, duct a small amount of conditioned air instead of exhausting to the vented sub-area.
Worked example
Using the values the calculator loads with:
Inputs
- Crawlspace floor area1200 sq ft
- Crawlspace typeSealed / encapsulated
Results
- Required airflow24 CFM
- TypeConditioned supply air
- Vapor barrierRequired regardless of type, 6-mil poly minimum
- Dehumidifier alt.A crawlspace dehumidifier sized for the volume can substitute for fan ventilation in sealed spaces
Frequently asked questions
Which is better, vented or sealed?
In humid climates, sealed/encapsulated crawlspaces perform much better and are increasingly code-preferred.
Do I still need a vapor barrier if I add a fan?
Yes — ventilation alone does not stop ground moisture; a vapor barrier is essential either way.
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.