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How do I size a Radon Fan?

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.

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.

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.

Learn how to properly size a radon fan for your home. How much cfm do I need? Understanding pressure field extension and radon levels. What size radon fan