Radon Fan CFM Calculator
Sub-slab depressurisation fan sizing.
Enter your values
Enter the slab area in sq ft.
Choose one of: Clean gravel, Sand, Soil / fine fill.
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.
- Target airflow
- 60 CFM
- Suction range
- 0.5 - 1.0 in wc
- Suction pits suggested
- 1
- Pipe size
- 3 in PVC
Quick answer
Radon fans are sized by slab area and sub-slab material, with tighter gravel needing higher suction and less airflow.
CFM ≈ area x rate for sub-slab material
At a glance
| What it does | Sub-slab depressurisation fan sizing. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Slab area, Sub-slab material |
| Main output | Target airflow |
| Formula | CFM ≈ area x rate for sub-slab material |
| Cost | Free — no sign-up, no download |
How to use the Radon Fan CFM Calculator
- 1Measure the slab footprint the system must cover.
- 2Identify the sub-slab material from a core sample or the builder's spec.
- 3Pick a fan whose curve delivers this CFM at the listed suction, then verify with a post-mitigation radon test.
Inputs explained
- Slab area(sq ft)
- Enter the slab area in sq ft.
- Sub-slab material
- Choose one of: Clean gravel, Sand, Soil / fine fill.
Worked example
Using the values the calculator loads with:
Inputs
- Slab area1200 sq ft
- Sub-slab materialClean gravel
Results
- Target airflow60 CFM
- Suction range0.5 - 1.0 in wc
- Suction pits suggested1
- Pipe size3 in PVC
Frequently asked questions
Does more CFM always help?
No — tight soils need high suction at low flow; an oversized flow fan just wastes energy.
Where does the pipe discharge?
Above the roof line and away from windows, per EPA guidance.
What do I need to enter into the Radon Fan CFM Calculator?
Just 2 values: slab area, sub-slab material. 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 Radon Fan CFM Calculator work out the answer?
Radon fans are sized by slab area and sub-slab material, with tighter gravel needing higher suction and less airflow. It applies the formula CFM ≈ area x rate for sub-slab material and shows the working so you can check each step by hand.
Is the Radon Fan CFM 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.