Reviewed and updated September 13, 2026. This article provides general public-health and referral guidance, not testing, medical, legal or engineering advice.
The liquid columns are showing pressure difference
Many active radon systems have a small U-shaped liquid gauge attached to the vent pipe. This is commonly called a manometer. When the fan creates suction in the pipe, the pressure difference moves the two liquid columns to different heights. That tells you the system is creating pressure relative to the surrounding air.
For homeowners in Elmira, Horseheads and Corning, the most important fact is what the gauge does not show: it does not measure pCi/L and it does not tell you the indoor radon concentration. A reading of '1' or '2' on a manometer is not a radon test result.
Your normal operating position is more useful than a generic target number
Different fans and systems operate at different pressure levels, so there is no universal manometer number that every house should show. What matters to the homeowner is whether the gauge remains near the normal position documented when the system was working properly.
If the columns that were clearly separated become equal, the fan may have stopped or the system may have lost suction. A major change from the normal position can also indicate a system condition worth checking. Take a photo of the gauge when the system is known to be operating correctly and keep it with the system records.
A normal gauge does not guarantee a low radon result
A system can create suction at the pipe while failing to control every foundation zone. For example, a second slab, crawlspace or addition may not communicate with the suction point. That is why a post-mitigation radon test is required to verify performance rather than relying on the gauge alone.
If the manometer looks normal but a valid indoor test remains high, use the radon-still-high-after-mitigation guide. The next step may involve system diagnostics instead of replacing a fan that is already running.
A changed gauge plus new noise or silence deserves attention
The warning device is most useful when combined with other observations. If the gauge changes at the same time the fan becomes silent, an alarm activates or a breaker trips, request service. If the fan becomes much louder or begins vibrating and the gauge also changes, note both symptoms for the technician.
Do not adjust the gauge tubing, fan or electrical connection simply to restore the old visual reading. The system should be diagnosed as a whole. The noisy radon fan guide explains why vibration and fan selection are system issues rather than just sound problems.
Use the gauge for routine awareness and radon testing for verification
New York requires an active radon reduction system to have a warning device that can alert the homeowner if the system stops working properly. Make checking that device part of normal home maintenance, especially after power outages, exterior work or anything that may have affected the piping.
Then keep testing on the schedule recommended by current public-health guidance. The gauge can tell you that the fan is creating a pressure difference today; only a radon measurement can tell you whether indoor concentration remains controlled over time.
Sources
Primary guidance used for this article
We use government and public-health sources, distinguish historical datasets from current household measurements, and do not invent local results. Read our editorial policy.