How Does Radon Mitigation Work? A Huntsville Homeowner's Guide

What is Radon Mitigation and how does it work?

Radon mitigation is a system that pulls radon gas from under your home's foundation and vents it safely above the roofline, so it never builds up inside your living space.

Radon is a radioactive gas that comes from the natural breakdown of uranium in the soil. It seeps up through cracks in your slab, gaps around pipes, and any other opening in your foundation. Once inside, it can get trapped and accumulate to levels that are dangerous to breathe over many years.

A standard mitigation system, called an active soil depressurization system, uses a fan to create a vacuum under your slab. That vacuum pulls the radon-laden air out from below your house and sends it through a PVC pipe that runs up the side of your home and out above the roofline. The fan runs continuously, 24/7.

Think of it like a straw. The fan is constantly sucking air from the gravel layer or dirt under your slab, and that air gets dumped outside where it dilutes harmlessly in the open atmosphere. The key is that the system keeps the pressure under your slab lower than the pressure inside your house, so radon never gets a chance to be drawn inward.

In Huntsville, most homes are built on a concrete slab, but some have crawlspaces or basements. Each foundation type needs a slightly different setup, but the principle is the same. The goal is to get the radon level inside your home down to below 4 picocuries per liter, which is the EPA's action level.

The system is not complicated. It has three main parts: a suction point (usually a hole cut in the slab), a fan mounted somewhere accessible, and a vent pipe that exits above the roof. A manometer, which is a little U-shaped tube with colored liquid, tells you at a glance whether the fan is working.

How Radon Mitigation works, step by step

A radon mitigation installation takes a few hours, starts with a diagnostic test, and ends with a retest to confirm the system is working.

The first step is always a diagnostic test. Your installer will drill a small hole in the slab, insert a tube, and measure the pressure field extension. This tells them how far the vacuum will reach under your slab. If the soil is tight clay, the vacuum may only pull a few feet, so they may need more than one suction point.

Next comes the suction point. The crew cuts a 4-inch or 5-inch hole through the slab, usually in a utility closet, the garage, or a basement corner where it won't be in the way. They dig out a small pit below the slab to create a pocket of air for the suction to work from. Then they glue in a PVC pipe that goes straight up.

The pipe runs up the interior or exterior of the house. Interior runs are cleaner looking but require cutting through floors and closets. Exterior runs are faster and cheaper, but the pipe is visible on the outside wall. In Huntsville, exterior runs are common because they don't disturb finished living space.

The fan goes in the attic, on the exterior wall, or in the garage. It has to be above the suction point and below the roof exit. The fan is the heart of the system. A good fan runs quietly and uses about as much electricity as a 60-watt light bulb.

The final piece is the vent pipe that goes through the roof. It has to extend at least 10 feet above ground level and at least 2 feet above any window or opening. That keeps the radon from being pulled back inside through an open window. The crew seals every hole they cut with caulk or flashing to keep the roof watertight.

After the install, the system gets a 48-hour follow-up test. That is the only way to know for sure the radon level dropped. Most systems in Huntsville bring levels from 10 or 20 pCi/L down to below 2 pCi/L.

Why Radon Mitigation matters for your home

Radon is the second leading cause of lung cancer after smoking, and it is completely invisible. Mitigation is the only way to fix a high level.

You cannot see radon. You cannot smell it or taste it. The only way to know it is there is with a test. The EPA and the Surgeon General agree that radon causes thousands of lung cancer deaths every year in the U.S. For nonsmokers, it is the number one cause.

Huntsville sits on the Tennessee Valley, which has a lot of limestone and shale underneath. Those rock types tend to release more radon than others. The Alabama Department of Public Health has found that many homes in Madison County test above 4 pCi/L. Some test at 20 or even 50 pCi/L.

A mitigation system is not a luxury. It is a straightforward fix for a real health risk. The cost is comparable to a new water heater or a decent appliance, and it runs for years with almost no maintenance. The fan typically lasts 5 to 10 years, and replacing it costs a fraction of the original install.

If you are buying a home in Huntsville, a radon test is part of most home inspections. If the level comes back high, the seller often pays for mitigation as part of the negotiation. If you already own your home, testing is cheap and easy. You can buy a test kit at a hardware store or online for about 15 dollars.

The real cost is not the system. The real cost is the risk of doing nothing. A mitigation system is the only way to bring a high level down. Opening windows helps in the short term, but it is not a solution. In winter, nobody keeps windows open, and radon builds right back up.

Common problems and what causes them

Most radon mitigation problems come from a broken fan, a blocked pipe, or a foundation that was not sealed properly.

The most common issue is a fan that stops working. The fan runs 24 hours a day, 365 days a year. After 5 to 10 years, the bearings wear out. You will know because the manometer fluid goes flat on one side. If the fan fails, the radon level will go back up within a day or two.

Another problem is a blocked vent pipe. Birds, wasps, or debris can clog the roof vent. A screen over the top helps, but it can also get clogged with ice or dirt. If the pipe gets blocked, the fan works harder and may burn out faster. The radon level may not drop as much either.

Poor sealing is a big one. If the crew did not seal the sump pit, the crawlspace vents, or the gaps around pipes, the system will still pull radon, but it will also pull conditioned air from inside your house. That wastes energy and makes the system less effective. In Huntsville, a lot of older homes have unsealed crawlspace vents that need to be closed up.

Sometimes the system was installed in the wrong spot. If the suction point is too close to a wall or a footer, the vacuum cannot reach the whole slab. That leaves a pocket of high radon on the far side of the house. A good installer checks the pressure field extension during the diagnostic test to avoid this.

A less common but real issue is a radon system that causes a backdraft. If your home has a gas water heater, a furnace, or a fireplace, the mitigation system can pull air down the chimney or flue. That can bring carbon monoxide into the house. A professional installer will test for this and add a fresh air intake if needed.

Common questions about Radon Mitigation