The most effective way to remove radon from a basement is a sub-slab depressurization system, which uses a fan and PVC pipe to pull radon gas from beneath your foundation and vent it safely above your roof. The EPA recommends taking action if your home tests at or above 4 pCi/L, and suggests considering mitigation even between 2 and 4 pCi/L, since there is no known safe level of radon exposure.
Radon is a naturally occurring radioactive gas that seeps up through soil and enters basements through cracks, gaps, and openings in the foundation. It’s the second leading cause of lung cancer. At 4 pCi/L, about 7 out of 1,000 nonsmokers exposed over a lifetime could develop lung cancer. For smokers, the risk jumps dramatically to about 62 out of 1,000 due to the combined effect of radon and tobacco smoke.
Sub-Slab Depressurization: The Gold Standard
Active soil depressurization, or ASD, is the method professionals install in the vast majority of homes with elevated radon. The concept is straightforward: one or more PVC suction pipes are inserted through or beneath your basement slab into the gravel or soil underneath. A continuously running fan draws soil gas (including radon) through those pipes and exhausts it above your roofline, where it disperses harmlessly into outdoor air.
The system works by creating a low-pressure zone beneath your entire basement floor. Because the pressure under the slab is now lower than the pressure inside your basement, radon gas gets pulled downward and into the pipes instead of rising up through cracks and into your living space. Think of it like a vacuum running underneath your foundation around the clock.
Several factors determine how well the system performs. The gravel layer beneath your slab needs to allow air to move freely so suction can spread across the full footprint of your basement. The fan needs enough power to maintain adequate suction at the flow rates your soil conditions create. The piping should be designed to minimize air resistance so the fan’s energy goes toward pulling gas from the soil rather than just pushing air through the pipes. And major openings in the slab or foundation walls need to be sealed so the suction field stays focused underground rather than pulling conditioned air from your basement.
Most homes need just one or two suction points, but the exact number depends on the size of your basement, the type of soil beneath it, and how well air communicates through the sub-slab material. A qualified installer will often do a diagnostic test, drilling a small hole and measuring how far suction extends beneath the slab, before finalizing the design.
Sealing Cracks and Openings
Sealing cracks in your basement floor and walls is a useful step, but it won’t solve a radon problem on its own. The EPA describes crack sealing as “a basic part of most approaches to radon reduction,” meaning it supports other methods rather than replacing them. Radon can migrate through porous concrete itself, not just through visible cracks, so even a perfectly sealed floor won’t stop the gas entirely.
That said, sealing improves the performance of a depressurization system by reducing the number of entry points and helping maintain that low-pressure zone under the slab. Fill all cracks and construction joints with appropriate sealant, not just a thin bead of caulk. For broader coverage, a thick epoxy coating (over 10 mils dry film thickness) applied to the entire floor adds another barrier. Pair this with a sub-slab system for the best results.
Sealing Your Sump Pit
If your basement has a sump pump, the open pit is a direct pathway for radon to enter your home. Covering it with a gas-tight lid is one of the simplest and most impactful things you can do as part of a mitigation plan.
Look for a sump cover made of rigid plastic or similar durable material with a built-in gasket that seals the entire rim of the pit. The cover should have air-sealing grommets around every penetration for electrical wiring, the water ejection pipe, and (if applicable) a radon vent pipe. Fasten it mechanically with screws to keep tight contact between the lid, gasket, and pit rim. Some systems route a radon suction pipe directly into the sealed sump pit, using it as a convenient below-slab collection point.
The ideal setup uses a low-point drain to collect water underground and pipe it into the sump pit from the side, below grade. This allows the top of the pit to stay permanently sealed with a solid, airtight cover.
Ventilation as a Supplemental Approach
Increasing ventilation in your basement dilutes radon by bringing in outdoor air, and a heat recovery ventilator (HRV) does this more efficiently than simply opening windows. An HRV uses the outgoing air to warm or cool the incoming air, reducing the energy penalty of constant ventilation.
HRVs work best when they ventilate only the basement rather than the whole house, concentrating their dilution effect where radon levels are highest. When properly balanced and maintained, they provide a steady rate of air exchange year-round. However, their effectiveness is limited by how much ventilation air they can move. They won’t reduce very high radon levels the way a depressurization system can, and they do increase heating and cooling costs, though less than ventilation without heat recovery.
For most homes, an HRV is better suited as a complement to a sub-slab system rather than a standalone fix. In homes with only moderately elevated levels (closer to 2 to 4 pCi/L), an HRV alone might bring numbers down enough, but testing afterward is essential to confirm.
Crawl Spaces Need a Different Approach
If your basement includes or connects to a dirt-floor crawl space, the mitigation strategy changes. Exposed soil is a major radon entry point that you can’t depressurize in the same way as a concrete slab. The standard approach is to cover the entire crawl space floor with heavy-duty polyethylene sheeting (6 mil thickness), seal the edges to the foundation walls, and then install a vent pipe and fan beneath the sheeting. This creates a sealed membrane that functions similarly to a concrete slab, allowing sub-membrane depressurization to pull radon from the soil and exhaust it outdoors.
A 4-inch layer of clean, coarse gravel beneath the plastic improves airflow and helps the suction field extend across the full area. The vent pipe runs vertically through the house and out the roof, just like a standard sub-slab system.
What Installation Looks Like
A professional radon mitigation typically takes half a day to a full day. The installer drills one or more holes through your basement slab, inserts PVC piping, and routes it to the exterior of your home and up past the roofline. The fan is usually mounted in the attic or on the exterior of the house, not in the basement, so you won’t hear it constantly. Most homes can be fixed for about the same cost as other common home repairs, comparable to what you’d pay for a new water heater or similar project.
After installation, you should wait at least 24 hours before testing and then run a short-term radon test (typically 2 to 7 days) with the system operating. Place the test kit in the lowest livable area of your home, which is usually the basement where the system was installed. If levels are still above 4 pCi/L, the installer may need to add suction points, increase fan power, or seal additional entry routes.
Keeping Your System Working Long-Term
A sub-slab depressurization system runs continuously and requires minimal maintenance, but it does need periodic attention. Most systems include a simple gauge or indicator on the pipe that shows whether the fan is creating suction. Check this every few months. If the indicator shows no pressure difference, the fan may have failed and needs replacement. Fans typically last 5 to 10 years.
Retest your home’s radon levels every two years, or anytime you make significant changes to your foundation, HVAC system, or home structure. Radon levels fluctuate with seasons, soil conditions, and changes in how your home moves air, so a system that worked perfectly at installation can occasionally need adjustment. Long-term test kits (90 days or more) give you the most accurate picture of your average exposure.