How do I size a Radon Fan?

What radon fan is right for my home?

We often hear customers ask, “what cfm does my radon fan need?” or “how big of a radon fan do I need?”.  These are difficult questions.  In the HVAC world, fans are always placed on a specified duct size (4″-10″+).  Manufacturers can accurately predict how much cfm an inline fan will move in these ducts.  However, with radon fans, you’re at the mercy of soil conditions, sub slab fill, suction pit sizing, and much more.  Meet the fan curve: Fan curves tell you how much cfm you’re moving at a given resistance or suction (measured in inches of water column pressure).  This is why you’ll often hear us ask you for a U tube reading.

Radon fan sizing can be difficult even for licensed mitigators, not to mention do-it-yourselfers.  When sizing a radon fan, there’s only one thing that matters: PRESSURE FIELD EXTENSION.  Pressure field extension simply means: how far am I drawing radioactive air from beneath my home?  It’s typically determined by taking specific measurements using a suction point and micro-manometer.  For the DIYer, these tools are cost-prohibitive.  If you want your radon mitigation system done right, always call a licensed, certified radon mitigator.

What am I getting myself into??

In order to estimate your fan size for yourself, you’ll need three things:

  1. Size of the building footprint (in square footage)
  2. Current radon level (long-term test, if possible)
  3. Building type
    • slab on grade
    • basement
    • walkout
    • tri-level or garden level
    • crawlspace, etc.
    • mixed (how many sq ft of each type)

It is for this reason, that it’s impossible to size a radon fan before the building is completed and a radon level has been established.

With this information, PDS can help you size a fan by phone or email

PDS’ phone estimations are just that: estimations.  Unfortunately, PDS does not take returns on DIY fan installs.  Take accurate measurements and be confident in your selection.  PDS is here to help.  The only folks with a guarantee are radon mitigation professionals performing contracted work.

Tips on fan sizing:

  • Use a suction pit pro and dig a large suction pit (at least 15-20 gallons [3-4 “home depot” buckets] of dirt and debris).   Dirt augers are helpful tools for this job.
  • Always use a manometer.  PDS cannot help diagnose fan issues if we cannot calculate airflow and static pressure.
  • Be prepared to change fans or add a second system on the opposite end of the home.
    • Even mitigators with decades of experience sometimes come up short.  It’s not always as simple as adding a “bigger” fan.
  • Know what’s under your home:
    • request foundation plans from the original owner/home builder
    • 4″ gravel base or just dirt?
      • clay?  sand?  something else?
    • Were radon-ready new construction techniques used?  If so, what products were installed? (Home builder should have a record)
      • Typically, with properly designed RRNC homes, a low wattage, low-volume fan can be used like the Fantech Rn1 or the RadonAway RP145
  • How to Video: Understanding Fan Curves for performance calculations



PDS supports the Indoor Environments Association