Radon mitigation fan running, but u-tube manometer shows no pressure differential

radon

We moved into this house in New Hampshire a year ago. Tons of radon off-gassing in this area due to granite rock substrate . Home inspection showed that the mitigation system was functioning properly, long-term test results below 2 pc/L. Recently I noticed that the manometer was showing equal readings on both sides of the u-tube. I don't recall what the level was during the home inspection. There are no marks I can see on the gage. When I turn off the breaker powering the fan, there is no change on the manometer. The fan is running; I climbed up and stuck my face it the exhaust; it smells wet and musty like basement air. It inflated a plastic shopping bag immediately. The sump pit looks to be well-sealed with silicone caulk. But I also see a 3" diameter hole through the concrete slab that is covered with a thin piece of cardboard. I can hear it whistling, and when I put my hand in the hole I can feel suction. Is there anyway for me to gain confidence in this radon mitigation system without hiring a contractor?

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Best Answer

Our u-tube shows a 2" WC. IMO, the hole is the problem: the pump is sucking air from the basement, making both sides of the tube at the same (basement) pressure. Hence, 0 pressure difference. This will obviously reduce the suction from the subsoil; at the same time, it will be pulling radon-contaminated air from the basement. I have no idea what the net effect would be.

You could get a continuous radon monitor. (Amazon, $130) Not cheap, but I find ours very reassuring.

FYI, a couple of things, from experience with our system. (It doesn't seem like these apply to your problem, but just in case.)

  1. We've had the outlet ice up in winter. (Moist air from sump, cold pipe.) When this happened, we showed 0 pressure.
  2. We've had problems in summer, where a water bubble developed in the u-tube. This affected the reading, but I don't remember how much. At the time, we were drawing outside air into the basement, and getting a lot of condensation. So, warm air, u-tube in contact with the cold pipe. We now keep the cellar mostly closed in summer, and I spaced the tube out from the pipe.
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