Our house had an existing radon pipe (passive) and high radon levels. We had a radon mitigation company assess the system. He installed a fan to the existing pipe. The fan is in the attic. Since the fan was installed, there is a loud thumping noise coming from the walls 24/7. It’s coming from the radon pipe - you can hear it inside the house AND outside the house coming from the radon pipe. The pipe exits the roof above our master bedroom. The fan is installed in the attic. When you place ear to wall you can hear water in the pipe. It’s so loud that it keeps you awake at night. I want a radon system that works. Should we start over or is there a way to fix this problem? Is the water being pulled into the pipe from under the basement floor? We have a finished walkout basement.

  • This question almost reads like an Edgar Allen Poe poem. How long has it been since the fan was installed? The first thing I would do is try to bring the radon mitigation company who installed the system back to assess what's wrong with their solution. Feb 14, 2021 at 15:24
  • If you shut the fan off, does the thumping continue? Feb 14, 2021 at 18:18

3 Answers 3


Without seeing the details of your piping, can't say for sure where the water might be coming from. But, the "intake" pipe for the radon exhaust, usually coming off of a sump pump well or pit, should not be going into any water.

Our previous house had a similar radon mitigation system, but we never had to use it. The lower part of the pipe connected to a tight fitting lid on the sump well. It did NOT go down into the well itself, and so was never near the water that was in the sump well.


RadonBC here. Absolutely get your hopefully certified mitigator back on the job. They should "want" to know all these details. One good reason for attic fans is that you shouldn't hear them, period. Water could cause all of what you are experiencing. High water table, sub slab pressured water leaks, poor building perimeter drainage can all send water to your radon suction pit. Water at the right level in a sub slab fitting will slurp and set up random pipe movement as vacuum builds and releases, both of which you will definitely hear. This may show up on the utube manometer mandatory with all activations. New construction Radon pipe rough in quality is demonstrably variable. What should require a small fan, minimal electricity and no fan noise outside the attic should definitely not turn into what you are experiencing. You need to know and post a few things. Does the system reduce the Radon? What is the fan model, not just the brand? Where are you? At some point you need to determine the water source and static level. What level of vacuum and airflow is your fan operating at? Was there any manometer measured vacuum field communication to correctly size your fan? Let me know. CNRP 201694.

  • ....aaaaaaand you want a Radon meter NOT a Geiger counter.
    – RadonBC
    Feb 19, 2021 at 1:44

There are two approaches to radon control:

  • Pump air out of the basement. This can be passive -- just having a pipe in the air part of the sump pump pit and going out the roof will pull a steady stream of air due to the stack effect. This can be augmented with a small fan.

  • Pump air INTO the house. This requires a tight enough house to maintain a higher pressure inside that out. Do this and air leaks out through all the leaks in the basement. Radon atoms aren't salmon that can swim against the current.

I suggest you edit your question with more details: How does the pipe run, what diameter? Make and model if there is such. Does the pipe have low spots that could trap water.

You also may want to buy a geiger counter. About $150 on amazon.

This article: https://www.ccohs.ca/oshanswers/phys_agents/radon.html?=undefined&wbdisable=true#:~:text=Radon%20is%20an%20invisible%2C%20odourless,radon%20daughters%20or%20%22progeny%22. gives more information about radon risk, and what various groups have set as reasonable exposure levels.

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