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Calculation Machine

Radon Fan CFM Calculator

Sub-slab depressurisation fan sizing.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
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.

The formula

CFM ≈ area x rate for sub-slab material

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Slab area1200 sq ft
  • Sub-slab materialClean gravel

Result

  • Target airflow60 CFM
  • Suction range0.5 - 1.0 in wc
  • Suction pits suggested1
  • Pipe size3 in PVC

How to use the Radon Fan CFM Calculator

  1. 1Measure the slab footprint the system must cover.
  2. 2Identify the sub-slab material from a core sample or the builder's spec.
  3. 3Pick a fan whose curve delivers this CFM at the listed suction, then verify with a post-mitigation radon test.

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.

About this calculator