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I have a radon system in my home with a u-tube style manometer. the reading over the past year has been almost 0*. I called the serviceman who told me it was fine as long as I could hear the fan running. *It is not a level 0- it has always been 1-2 millimeters higher on one side.

All of my neighbors meters show a drastic level difference. Is this normal?

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Have you already attempted to recalibrate the meter? –  BMitch Jan 3 '13 at 18:02
    
It is a u-tube manometer (filled with liquid)- it does not require calibration –  user9892 Jan 3 '13 at 18:55
    
Are there any leaks in the system, perhaps you can do some type of smoke test? –  BMitch Jan 3 '13 at 19:02
    
Your only safe/authoritative source for this answer is the documentation provided by the manufacturer of your radon system. If a manometer reading of "essentially 0" is acceptable, and the only necessary safeguard is the "sound of a fan", then why waste the time and money to install a manometer at all? It's intuitive to me that there could be something that is materially affecting the fan's ability to move air. That would explain the manometer being "almost 0". But no one except the system manufacturer can say exactly how much manometer differential is necessary for safe operation. –  Bob Jan 3 '13 at 19:12
    
are the two sides the same height or is one taller? If one is taller, then it sounds like it's working. –  DA01 Jan 3 '13 at 23:33
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1 Answer

A u-tube doesn't need calibration in the respect that the difference between the two scales will be twice the static suction. For convenience though, in order to read accurately from 0, it should be "calibrated", because some oil will slowly be lost over the years. Simply disconnect the tops of the tube and slide it until the oil level is even with the zero reading. Replace the connections.

How different the levels are will depend on the accuracy of the device and the size of the fan, among other factors. What's important is what was the reading when the system was new? That should have been documented after installation and posted. If the current reading is significantly different, the cause should be determined and corrected.

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