How Do You Know If Your Radon Mitigation System Is Working?
If your home has a radon mitigation system, you've probably walked past it a hundred times: a white PVC pipe coming out of the basement floor, a fan in the attic, garage, or outside, and a little U-shaped tube of colored liquid on the pipe. Once it's installed, most people forget about it.
But a radon system is a mechanical system, and like a furnace, it can wear out or quit. Since you can't see or smell radon, you won't notice if it does. The only way to know for sure it's working is to test the house. Between tests, that U-shaped tube filled with liquid can give you an early heads-up if you know how to read it.
The only way to truly know if a radon mitigation system is working is to test your home's radon level, and the EPA recommends retesting at least every two years. Between tests, check the system's warning device, usually a U-shaped tube manometer on the radon pipe. When the fan is running, the liquid on the side connected to the pipe sits higher than the side open to the room, which shows the pipe is under negative pressure. If the two columns are even, or the reading has dropped well below the mark on the label from installation, the system may not be working and should be checked by a qualified radon mitigation contractor.
How does a radon mitigation system work?
The most common type, called active sub slab suction, runs a pipe through the basement floor or slab into the soil underneath. A fan on that pipe pulls radon from under the house and vents it above the roof, where it quickly mixes with the outdoor air. That suction also creates a slight vacuum under the slab, which helps keep radon from being drawn into the house.
The EPA says the fan should never be turned off. It has to run continuously to work. If your system is passive (a pipe with no fan), there's no suction to measure, so testing is the only way to check it.
What is the only way to know if a radon system is working?
Only a radon test tells you the actual radon level inside your home. The EPA recommends retesting a home with a mitigation system at least every two years, and the ANSI/AARST standard for radon mitigation in homes calls for the same.
Why keep testing a system that worked when it was installed?
Fans wear out. The EPA says radon fans may last five years or more, and manufacturer warranties tend not to go past five years.
Houses change. Finishing a basement or adding on can affect how well a system works. The EPA recommends retesting in the lowest lived-in area after you remodel.
The gauge only shows suction. A good reading on the pipe tells you the fan is pulling. It can't tell you the radon level in the rooms you live in.
How do you read the manometer on a radon pipe?
That U-shaped tube is called a manometer, and it's the most common warning device on a fan-powered radon system. One side has a small hose running into a hole in the radon pipe, and the other side is open to the room. When the fan runs, its suction pulls the liquid up on the hose side.
When the system is working, the liquid on the side with the hose going to the pipe sits higher, and the liquid on the side open to the room sits lower. That uneven reading means the pipe is under negative pressure, which is what you want.
If the two columns have evened out, the fan has likely stopped, or another part of the system isn't working. If the liquid on the suction side has dropped well below the line or number your installer marked on the label, something has changed. Every system is set up a little differently, so there isn't one right number for every house. Compare today's reading to the mark from installation day and pay attention to the baseline level mark on the system.
Either way, the EPA says to call a contractor to have the system checked. The Missouri Department of Health and Senior Services (DHSS) recommends a mitigation contractor certified by the National Radon Proficiency Program (NRPP).
The EPA recommends checking your warning device regularly, whether it's a manometer, an alarm, or a light. An easy habit is to glance at it when you change your furnace filter.
Buying or selling a home with a radon mitigation system?
A mitigation system tells you that someone found elevated radon at some point and did something about it. It doesn't tell you what the level is today. According to DHSS, no Missouri law requires radon testing during a sale or requires the seller to mitigate, so verifying the system is up to you.
A few home inspection tips for buyers:
Ask for the paperwork. Request past radon test results, the installer's name, and the warranty, including whether it transfers to a new owner.
Look at the manometer. Check it during your showing or your inspection, and bring up even levels with your agent right away.
Add a radon test to your inspection. A radon test runs at least 48 hours, and most inspection windows are only 10 to 15 days. Booking it with your inspection gets you a result with time left to negotiate.
Sellers planning a home inspection before selling should add a radon test, so there's a current result to hand buyers with the system paperwork.
Who should do the follow-up test?
After a new system goes in, the EPA recommends a test within 30 days, but no sooner than 24 hours after the system is running. The contractor may test their own work, but the EPA also recommends an independent test to avoid a conflict of interest, a concern DHSS raises too.
We're IAC2 certified for radon testing, we follow EPA protocols, and your report is ready within 24 hours of the device being picked up. We don't install mitigation systems, so our job is simply to give you an accurate number. If your levels come back high, we'll refer you to qualified mitigation professionals, and we can run the follow-up test once the system is in.
The bottom line
Glance at the manometer regularly, and call a mitigation contractor if the levels go even. Then test at least every two years, because a test is the only way to confirm your radon levels are where they should be.
Frequently asked questions
How often should you test for radon if you have a mitigation system? At least every two years, according to the EPA. You should also retest after major remodeling, like finishing a basement, since construction can affect how well the system works.
Does the manometer on a radon pipe measure radon? No. The U-tube manometer shows whether there's suction in the radon pipe. It can't measure the radon level in your home. Only a radon test can do that.
How do I know if my radon fan is working? Look at the manometer on the radon pipe. If the liquid on the side with the hose going to the pipe sits higher than the side open to the room, the fan is creating suction. If the levels are even, the fan has likely stopped or another part of the system isn't working.
What should my radon manometer read? There's no single correct number, since every system is set up differently. Compare the current reading to the line or number your installer marked on the label. If the suction side has dropped well below that mark, or the levels are even, have the system checked by a qualified radon mitigation contractor.
Can I turn off my radon fan? No. The EPA says a radon fan should never be turned off. It has to run continuously for the system to work.
How long does a radon fan last? The EPA says radon fans may last five years or more, and manufacturer warranties tend not to go past five years. After that, the fan may need to be repaired or replaced.
When should a new radon mitigation system be tested? The EPA recommends testing within 30 days of installation, but no sooner than 24 hours after the system starts running. An independent test from someone who didn't install the system avoids a conflict of interest.
Is radon testing part of a home inspection? No. A standard home inspection is a visual evaluation and doesn't measure radon. Radon testing is a separate service that can be added to your inspection and run at the same time.
Is your last radon test more than two years old?
Book a radon test on its own, or add one to your home inspection. See how our radon testing works, check current pricing, or schedule online. Same-week availability, weekend appointments, and your report within 24 hours.
Tech Inspect Home Services LLC · 3580 Highway T, Marthasville, MO 63357 · 636-201-6366 · sean@techinspecthome.com