Active radon mitigation is a system that uses a mechanical fan to continuously pull radon gas from beneath your home’s foundation and vent it safely outdoors. The word “active” distinguishes it from passive systems, which rely on natural airflow alone. It’s the most common and effective method for reducing indoor radon, capable of lowering levels by 50 to 99 percent.
How the System Works
Radon is a radioactive gas that seeps up from the soil through cracks and gaps in your foundation. An active mitigation system, technically called active soil depressurization, reverses that process. A fan connected to PVC piping creates suction beneath your concrete slab, pulling radon-laden air out of the soil before it ever enters your living space. That air travels up through the pipe and exits above the roofline, where it disperses harmlessly outdoors, far enough from windows that it won’t cycle back in.
The system doesn’t require major changes to your home. In most installations, a single pipe runs from below the slab up through the house (or along an exterior wall) to above the roof. The fan is placed in an unconditioned space like an attic, garage, or outside the home so that if any connection were to leak, radon would escape into an area you don’t breathe in rather than your living space. Cracks and openings in the foundation are also sealed to improve the system’s suction and prevent radon from bypassing the pipe.
Active vs. Passive Systems
A passive radon system uses the same basic pipe setup but has no fan. It relies on the natural stack effect, where warm air rising inside the pipe creates a gentle upward draft, to pull soil gases out. Many newer homes are built with a passive stack already in place, along with an electrical outlet in the attic near the pipe, so a fan can be added later if testing shows elevated radon.
The critical difference is performance. A passive system moves air slowly and inconsistently, and it often can’t reduce radon enough on its own. The EPA recommends activating the system by installing a fan whenever radon levels reach or exceed 4 picocuries per liter (pCi/L). Converting a passive system to active is straightforward for a qualified contractor, since the piping is already in place.
Why Radon Levels Matter
The EPA’s action level is 4 pCi/L. At that concentration, an estimated 7 out of every 1,000 nonsmokers exposed over a lifetime could develop lung cancer, a risk comparable to dying in a car crash. For smokers, the same level raises the estimate to about 62 out of 1,000, five times the risk of a fatal car accident. Because no level of radon exposure is considered completely safe, the EPA also recommends considering mitigation for levels between 2 and 4 pCi/L.
Radon is the second leading cause of lung cancer after smoking, and it’s the leading cause among people who have never smoked. An active system that brings your home from, say, 8 pCi/L down to 1 or 2 pCi/L meaningfully changes your long-term risk profile.
How to Tell If Your System Is Running
Every active system includes a simple monitoring device, usually a U-tube manometer, mounted on the pipe where you can see it. This is a small, liquid-filled glass tube shaped like the letter U. One side connects to the suction pipe, and the other is open to the surrounding air. When the fan is working, it creates a pressure difference that makes the liquid levels uneven, with the side connected to the pipe pulled higher. If the liquid sits at the same level on both sides, or reads zero, the fan has stopped working, likely due to a power loss, motor failure, or a break in the pipe.
A normal reading typically falls between 0.5 and 1.75 inches of water column. You don’t need to memorize that range, but checking the manometer periodically, maybe once a month, takes about two seconds and tells you immediately whether the system is doing its job.
Installation and Cost
Professional installation typically costs between $1,000 and $2,000. The price varies based on your home’s layout, foundation type, and local labor rates. The work usually takes less than a day and involves drilling a small hole through the slab, connecting PVC piping, mounting the fan, and sealing foundation cracks.
Soil conditions beneath your slab also influence the installation. Homes built on gravel or other porous fill allow suction to spread easily, so a single pipe and standard fan are often enough. Tight, clay-heavy soils restrict airflow and may require additional suction points or a more powerful fan to extend the pressure field across the full footprint of the foundation. Your installer should assess this during the initial evaluation.
Running Costs and Maintenance
Active systems run 24/7, which raises the question of electricity costs. Research from Lawrence Berkeley National Laboratory found that annual operating expenses average roughly $66 in the South and West and about $99 in the Northeast and Midwest. The fan itself accounts for about 60 percent of that cost. It’s comparable to running a single light bulb continuously.
Fans generally last five or more years, though manufacturer warranties tend to cap at five. When a fan eventually wears out, you’ll usually hear it first: increased noise, vibration, or a complete loss of suction that shows up on the manometer. Replacing a fan is a simpler and cheaper job than the original installation.
Testing After Installation
Once your system is activated, you should retest your home’s radon level within the first month, but no sooner than 24 hours after the fan is turned on. This gives you a baseline to confirm the system is working as expected. After that initial check, retesting at least every two years is the standard recommendation. You should also retest if you make significant changes to your home, such as finishing a basement, adding an addition, or altering the foundation in any way, since these changes can shift airflow patterns and affect how well the system performs.