Normal radon mitigation sucks out the air from underneath a house's foundation.

What if I ran the fan in reverse to blow this same air outward instead of sucking it upward? It seems either direction should be effective, so I am thinking that we choose to suck upwards just to avoid pushing it out towards neighbors. If sucking is truly more effective, how much more effective is it (in terms of radon pCi/L)? I imagine the difference in effectiveness depends on the season, whether the house is cooling or heating, so please consider both seasons. Of course, measured data comparing both fan directions for both seasons would be the best!

  • 1
    I rather doubt you'll get "data for both fan directions" as nobody does the backwards direction in real life. Or you can provide it yourself if you get a nice fast-response meter and turn your fan over, though I'm not too sure the bearings are even designed to run inverted.
    – Ecnerwal
    Commented Dec 11, 2022 at 23:46

2 Answers 2


The problem with this idea is that you don't really control where the radon-containing air will vent. You may actually end up pushing it into your living space.

With the suction setup that is used, the vented air goes up the tube and is safely exhausted away from living quarters.

  • Great answer, I was about to post the same thing. Any leaks could allow the radon into the home if the basement was pressurized to even a minimal extent. Commented Dec 11, 2022 at 16:44
  • Also dirt and rock tend to make good blocks for pushing air though unless the collection tubes come out the outside of the building.
    – crip659
    Commented Dec 11, 2022 at 16:54
  • The gas is a product of radioactive decay. you can't just pressurize it back into the rock. Commented Dec 11, 2022 at 17:01
  • This answer makes sense, but I want to believe that there is some benefit to positive pressure both in the living space and below the slab (if there is an outward venting path which avoids the living space), right? I am still hoping for some measurement data, so let me wait a few days before marking the answer.
    – bobuhito
    Commented Dec 11, 2022 at 17:26
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    Pressurizing the house requires that the path to "push" the radon back is easier (more porous) than the path out of the rest of the house. Every house will vary, but given that houses are pretty darn breathable, my instinct is that the house is more porous. Commented Dec 11, 2022 at 17:52

I've been wondering about this myself and found a paper from the early 90s that explored pressurizing the basement such that the gradient was equal or higher above the slab. The paper below indicates that it works well and I'm not quite sure why this isn't explored for houses with very poor material under the slab for SSD.


  • 1
    Why the downvote? Suction is probably the more reliable approach, but Table 4 of the paper does show that a 10x radon reduction can be achieved by basement pressurization of 2~3 Pa, right? Are you thinking that these houses still had pockets of high radon levels where the detectors were not placed? Anyway, I wish they would have done a fan reversal test in the same houses...
    – bobuhito
    Commented Mar 30, 2023 at 13:14

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