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Community and Q&A

Radon, Vents, and Air Leakage

dugdale | Posted in Energy Efficiency and Durability on

I have a home built by Richmond homes in 1995 in Superior Colorado. The basement floor is not concrete (soil issues), it’s dirt with a plastic covering and a few feet above that is a wooden basement floor. When we purchased the home 14 years ago the radon test came in around 4pCi/L so the original owner put in an active fan radon system for us before we moved in.

I have always wondered about two vents that run from the rim joist down below the basement wood floor. My guess is those two vents provide passive radon mitigation. It’s just a guess since radon gas is heavier than air and might not travel up the vent to outside.

Now that we have an active radon system can I block off those two vents to improve my blower door score (5.9 ACH before I started air sealing)?

I have an Airthings radon monitor and this time of year it is averaging 1.6pCi/L. If I close off those vents I will keep a close eye on the radon levels this coming winter.

I called Richmond homes and left a message weeks ago but they have not returned my call.

Am I right, are those two vents for passive radon mitigation?

(for those wondering, I have 2″ foam board behind that fiberglass at the rim joist.)

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  1. user-5946022 | | #1

    Please provide a bit more info. It is unclear what your situation is based on the description and the photo.
    Does the photo show what you believe to be a passive radon vent? Radon vents are usually made of PVC pipe. However, perhaps they made them of duct in the 1970s
    Are you sure the photo you posted of the duct is not some sort of supply or return duct for conditioned air or moisture control under your wood floor?

  2. dugdale | | #2

    Below is a picture of what is below my wood basement floor, I took this 14 years ago before the radon system went in and now it is hard to get down there around my stump pump to take another photo. If I could get down there my guess is I would see the duct opening up to this subfloor place. Here is another picture of the duct (I believe to be a passive radon vent) running from the subfloor to the rim joist.

    I know my ductwork pretty well since I have sealed a lot of it and I can say the chances of this duct being connected to my HVAC system is low.

    I also added a pic of my active radon system.

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