I have a fan powered radon mitigation system installed in my house. It was installed in 2016 and I have not had any issues with it until this winter. I live in northern Iowa where we have been getting some unusually extreme temperature variations this winter (10F - 55F on some days).

I believe the system is exhausting warm moist air which is then freezing within the 4" exhaust pipe. As the pipe heats above freezing, this ice releases and falls into the exhaust fan. This causes some extreme noises (Much like marbles in a blender) until the ice has been chopped to small enough pieces by the fan to fall further under the slab.

The installer claims that the fan is designed for this, but I have to think that this happening on a daily basis will shorten the life of the fan (Not to mention the whole house panic when this happens in the middle of the night (Due to loud noise)).

What are my options to prevent this ice from making noise and destroying my radon fan?

Note: Basement has no water issues, and radon manometer shows normal readings.

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  • 1
    Does it really need to go above the roof, given that there is two other exhausts right there, that if you stood in front of long enough, you'd die? (which are also too close to that operable window, but w/e)
    – Mazura
    Jan 6, 2019 at 23:53
  • The closest window is a window in a garage. I don't understand the characteristics of radon gas well enough to know what the impact would be if I move the radon vent to be near the other two. I assume there is a reason it was located above the roof line, and wouldn't want to impact safety (beyond what is existing with the other vents).
    – cyclops
    Jan 7, 2019 at 3:08
  • That's a tough situation with no obvious fixes other than a catch branch in the piping, but that could get ugly on the side of your house. I might tap the pipe with a wood block or mallet each evening during the troublesome weather to get the noise overwith.
    – isherwood
    Jan 10, 2019 at 22:19
  • Not an answer, but we also have ice formation. It can be seen at the (downturned) outlet, and is quite substantial when we have extended cold weather - enough blockage so the short-term reading goes up 2-3 pCi/L. But, no evidence of it hitting the blower. (15 years on)
    – George
    Jan 12, 2019 at 4:33

1 Answer 1


Maybe you could splice in some sort of 45 degree sanitary tee at that curve right above the fan? That way, when the ice falls down the pipe, it gets caught. Maybe also some kind of filter there to restrict airflow but allow water to melt out on warm days.

  • 1
    I went with this solution. I put in a tee right above the fan with 6 inches of pipe below to catch the ice. I checked it this morning and saw some ice had collected in there. I plan on putting a small hole in the cap to allow the water to drain out when it melts. I plan on making the hole small enough to not allow a huge amount of air to escape. Thanks!
    – cyclops
    Jan 14, 2019 at 16:38

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