Crawlspace Exhaust Fan Calculator
Fan airflow for a vented or sealed crawlspace.
Enter your values
Enter the crawlspace floor area in sq ft.
Choose one of: Vented, fan-assisted, Sealed / encapsulated.
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.
- 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
At a glance
| What it does | Fan airflow for a vented or sealed crawlspace. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Crawlspace floor area, Crawlspace type |
| Main output | Required airflow |
| Formula | CFM = area / 50 |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Crawlspace floor area(sq ft)
- Enter the crawlspace floor area in sq ft.
- Crawlspace type
- Choose one of: Vented, fan-assisted, Sealed / encapsulated.
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.
What do I need to enter into the Crawlspace Exhaust Fan Calculator?
Just 2 values: crawlspace floor area, crawlspace type. 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 Crawlspace Exhaust Fan Calculator work out the 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. It applies the formula CFM = area / 50 and shows the working so you can check each step by hand.
Is the Crawlspace Exhaust Fan 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.