# Radon Manometer

- **URL:** https://airsenseenvironmental.com/radon-manometer/
- **Published:** 2026-09-07

Skip to content Radon Mitigation Services ▾ Radon Testing Commercial Radon Mitigation Commercial Radon Testing Indoor Air Quality Crawl Space Encapsulation Service Area Resources FAQ Blog Podcast Reviews & Projects About Us Contact 314-664-9807 Free Estimate Radon Mitigation Services Radon Testing Commercial Radon Mitigation Commercial Radon Testing Indoor Air Quality Crawl Space Encapsulation Company Service Area Resources FAQ Blog Podcast Reviews & Projects About Us Contact Call 314-664-9807 St. Louis Metro · Missouri & Illinois Radon Manometer Radon Mitigation System Diagnostics NRPP-Certified Radon Pros MO & IL A radon manometer is the small U-shaped tube mounted on a radon mitigation vent pipe that shows whether the system's fan is pulling a vacuum, read by comparing the fluid height in its two legs. When the fan is working, the coloured fluid sits at two different heights. When both legs are level, the system is not moving air, and a failed fan is the usual cause. Checking it takes about ten seconds and is worth doing a few times a year. What a manometer cannot do is tell you the radon level in your home, which still requires a radon test against the EPA action level of 4.0 pCi/L. Call 314-664-9807 Get a Free In-Home Estimate IEMA Radon License #RNM20232346 Free Written Estimates Post-Mitigation Radon Testing What the Gauge Cannot Tell You EPA action level4.0 pCi/L Our design target< 2.0 pCi/L Systems are engineered to bring your home below the EPA action level of 4.0 pCi/L. Ten-second check Reading It How do you read a radon manometer? You read a radon manometer by comparing the fluid level in its two vertical legs. A difference in height means the fan is pulling a vacuum on the pipe. Equal heights mean it is not. Uneven columns: the system is under suction and running as designed Level columns: no vacuum in the pipe, which usually means the fan has failed or lost power A changed reading: if the difference is noticeably larger or smaller than it used to be, something in the system has changed, such as a blockage or a new leak Most installers mark the normal operating position on the gauge at the time of installation. That mark is the reference point, not any particular number, because the correct reading differs from house to house depending on soil and pipe resistance. Failure What does it mean when a radon manometer is level? A level radon manometer means the system is not pulling air, and in most cases the fan has stopped. It is the clearest single sign of radon system failure, and it is silent, which is why it goes unnoticed. The usual causes, in rough order of likelihood: Fan failure. Radon fans run continuously and wear out after several years. Lost power. A tripped breaker or an unplugged exterior outlet will stop the fan without any other symptom. A disconnected or cracked pipe. A break upstream of the gauge relieves the vacuum. A blocked pipe. Less common, but ice or debris can obstruct the discharge. If the columns have levelled out, the practical next step is radon fan replacement, followed by a retest. Limits Does a radon manometer measure radon levels? No. A radon manometer does not measure radon. It measures air pressure in the vent pipe, which tells you the fan is running but says nothing about the concentration of radon in your living space. The two can disagree. A system with a correctly placed suction point and a healthy manometer reading can still leave part of a slab untreated if the vacuum does not extend across the whole footprint. In that case the gauge looks perfect and the house is still above 4.0 pCi/L. This is why the EPA recommends retesting at least every two years after mitigation, and why every installation should end with post-mitigation radon testing rather than a glance at the gauge. Terminology Is a radon manometer the same as a radon thermometer? There is no such thing as a radon thermometer. People searching that phrase are almost always describing the manometer, because the U-shaped tube of coloured liquid on the pipe looks like a thermometer at a glance. The distinction matters because the two would measure completely different things. A manometer measures pressure difference. Temperature has no direct bearing on whether a radon system is working, though it does affect radon levels seasonally, with readings highest from December through February. Maintenance How often should you check a radon manometer? Check a radon manometer a few times a year, and any time you notice the fan has gone quiet or changed pitch. There is no maintenance to perform on the gauge itself. A reasonable routine: Seasonally, particularly at the start of the heating season when radon levels are naturally highest After a power outage, since the fan may not restart if a breaker tripped Before listing a home for sale, when a buyer's inspector will look at it Alongside a radon retest, which the EPA recommends at least every two years Local Conditions Radon manometer readings in St. Louis homes Normal manometer readings vary widely across the St. Louis metro because the soil under the slab varies. A system on loose aggregate in a newer St. Charles County subdivision may show a small pressure difference and still be depressurizing the whole slab. A system fighting compact clay in an older St. Louis County home may show a much larger difference on the same size fan. That is why the installer's reference mark matters more than any published number. Air Sense Environmental services systems it installed and systems installed by other contractors across Missouri and Illinois, and can confirm whether a reading is normal for that specific system. See radon mitigation for the full service. Common Questions Frequently Asked Questions About Radon Manometers What should a radon manometer read? A radon manometer should read whatever your installer marked as its normal operating position, because the correct value differs by house. What matters is that the two fluid columns sit at different heights and stay near that mark. There is no universal target number, since soil density and pipe resistance change the pressure a healthy system develops. Why is my radon manometer showing zero? A radon manometer showing zero, meaning both columns level, indicates the system is not pulling air. The most common cause is a failed radon fan, followed by lost power to the fan and then a disconnected or cracked pipe. Radon levels will climb back toward pre-mitigation readings while the system is down, so it should be diagnosed promptly. Can a radon manometer be wrong? A radon manometer can be misleading rather than wrong. It accurately reports pressure in the pipe, but pressure is not the same as performance. A system can hold good suction at the gauge while failing to depressurize the full slab, which leaves part of the house untreated. Only a radon test measures the outcome. Does the fluid in a radon manometer need to be refilled? Normally no. The coloured fluid in a sealed U-tube manometer is not consumed and should last the life of the gauge. If the fluid has visibly dropped or discoloured, the gauge has likely been damaged or leaked and should be replaced, which is a small job compared with the rest of the system. Does a moving manometer mean my radon level is safe? No. A moving manometer confirms the fan is pulling a vacuum on the pipe, not that indoor radon is below the EPA action level of 4.0 pCi/L. A radon test is the only way to confirm the concentration in the house, and the EPA recommends retesting at least every two years after a system is installed. References: EPA radon action-level guidance and A Citizen's Guide to Radon. Not Sure What You Are Looking At Send us a photo of your manometer Call and we will walk through the reading with you. If the columns have levelled out, we can usually get a fan replaced in one visit. Get a Free In-Home Estimate 5237 Old Alton Edwardsville Rd Edwardsville, IL 62025 314-664-9807 · Open 24 hours IEMA License #RNM20232346 Services Radon Mitigation Radon Testing Commercial Radon Radon Fan Replacement Sub-Slab Depressurization Crawl Space Encapsulation Company About Us Service Area Reviews & Projects FAQ Resources Contact © 2026 Air Sense Environmental. All rights reserved. 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