The most effective way to reduce radon in a basement is to install an active soil depressurization system, which uses a fan and PVC piping to pull radon gas from beneath your foundation and vent it above your roofline. This method works for the vast majority of homes and typically brings radon levels well below the EPA action level of 4 pCi/L. Most professional installations cost between $786 and $1,274, with a national average around $1,028.
How Radon Gets Into Your Basement
Radon is a naturally occurring radioactive gas that forms in soil as uranium breaks down. It seeps upward through the ground and enters your basement through any available path: cracks in the foundation slab, gaps around pipes, joints where walls meet the floor, sump pits, and even through porous concrete itself. Because basements sit partially or fully underground and are enclosed, radon accumulates to concentrations far higher than outdoor air.
The pressure inside your home is often slightly lower than the pressure in the soil beneath it, especially in winter when warm air rises and escapes through upper floors. This pressure difference actively draws soil gases, including radon, into your basement like a gentle vacuum.
When You Need to Take Action
The EPA recommends fixing your home if radon levels reach 4 pCi/L (picocuries per liter) or higher. There is no “safe” level of radon exposure, but 4 pCi/L is the threshold where the EPA considers the health risk significant enough to warrant mitigation. If your test results fall between 2 and 4 pCi/L, reducing levels is still worth considering, since radon exposure is the second leading cause of lung cancer after smoking.
Short-term test kits (available at hardware stores for under $20) give you a preliminary reading in 2 to 7 days. If the result comes back at or above 4 pCi/L, follow up with a long-term test or a second short-term test to confirm before investing in a mitigation system.
Active Soil Depressurization: The Standard Fix
Active soil depressurization (ASD) is the gold standard for radon reduction. A contractor drills a hole through your basement slab (typically 4.5 to 6 inches across), excavates a small pit in the soil below it, inserts a PVC pipe, and runs that pipe up through or along the side of your house to a point above the roofline. An inline fan mounted in the pipe creates constant suction beneath the slab, pulling radon-laden soil gas up and out before it can enter your living space.
The suction pit beneath the slab helps distribute negative pressure across a wider area under the floor. These pits are usually 1 to 3 feet in diameter and 4 to 18 inches deep, excavated by hand through the drilled hole. In homes with tightly packed soil, this pit matters more because the gas doesn’t move as freely on its own.
Standard systems use 4-inch rigid PVC piping, though 3-inch pipe is sometimes used for a cleaner look in visible areas. Flexible ducting or dryer hose should never be used in any part of the system. Horizontal pipe runs need a slight downward slope (about 1 inch of drop per 4 to 100 linear feet) so condensation drains back into the ground rather than pooling in the pipe.
Fan selection depends on conditions beneath your slab. Homes with gravel or loose fill under the concrete allow air to flow easily, so a standard 90-watt centrifugal fan handles the job. Homes with dense clay or tightly packed soil restrict airflow and may need high-suction blowers designed specifically for radon mitigation, capable of generating significantly more suction at lower airflow rates.
Passive Systems and When to Upgrade
Some newer homes are built with a passive radon stack: a vertical PVC pipe running from beneath the slab up through the roof, with no fan. These rely on the natural stack effect (warm air rising) to pull soil gas upward. In many cases, a passive stack alone isn’t enough. If testing shows radon at or above 4 pCi/L, the fix is straightforward: a qualified contractor installs an inline fan in the existing pipe to convert it into an active system. This upgrade is simpler and cheaper than starting from scratch because the piping is already in place.
Crawl Spaces and Dirt Floors
If your basement has an adjacent crawl space with an exposed dirt floor, or if the basement floor itself is dirt or badly deteriorated concrete, active soil depressurization alone won’t work. Instead, contractors use a technique called sub-membrane depressurization. A heavy-duty vapor barrier is sealed over the exposed soil, attached to the foundation walls, columns, and any pipes penetrating the floor. Before the membrane goes down, perforated pipe or a gas collection mat is laid on the soil surface and connected to a vertical vent pipe leading to a fan.
The fan creates negative pressure beneath the sealed membrane, capturing radon before it can escape into the crawl space and migrate into the basement. The membrane needs to be durable enough to handle foot traffic if the space is used for storage or mechanical access. Contractors often install protective matting over the barrier in walkable areas. Pressure sensors or monitoring ports built into the system let you verify it’s working over time.
Sealing Your Sump Pit
An open sump pit is one of the easiest paths for radon to enter your basement. Sealing it with an airtight cover is a simple step that makes any mitigation system more effective. Purpose-built sump covers use thick polycarbonate lids (rated for 200 pounds, so you can step on them) with gaskets that create an airtight seal. They include ports for the discharge pipe, a drain inlet for floor water, and a removable access plug for cleaning.
Many radon contractors connect a suction pipe directly to the sealed sump pit, using it as one of the depressurization points in the system. This serves double duty: it keeps your sump pump functional for water management while pulling radon from the gravel bed beneath your basement floor.
Ventilation as a Supplemental Approach
Heat recovery ventilators (HRVs) reduce radon by diluting basement air with fresh outdoor air. They recover most of the heating or cooling energy from the outgoing air, so your energy bills don’t spike dramatically. HRVs are more effective when ducted to ventilate only the basement rather than the whole house, concentrating the dilution effect where radon levels are highest.
The limitation is that HRVs produce variable radon reduction depending on how high your levels are and how much ventilation the unit provides. They work best as a supplement to soil depressurization, not a replacement. If your radon levels are significantly above 4 pCi/L, an HRV alone is unlikely to solve the problem. The filters in these units need cleaning regularly and replacement about twice a year.
Sealing Cracks and Gaps
Sealing visible cracks in your basement slab, gaps around utility penetrations, and the joint where the floor meets the foundation wall can reduce radon entry points. Use polyurethane caulk for narrow cracks and hydraulic cement for larger gaps. On its own, sealing rarely brings radon below the action level because the gas finds paths you can’t see or reach. But sealing makes your depressurization system work better by reducing the amount of basement air being pulled down through the slab, allowing the fan to maintain stronger suction across a wider area.
What Installation Looks Like
A typical installation takes one day. The contractor identifies the best suction point (usually near the center of the basement for maximum coverage), drills through the slab, excavates the pit, and runs piping either up through interior closets and the attic or along an exterior wall to above the roofline. The fan is mounted in the attic, garage, or on the exterior pipe run, always outside the living space. This is important: if the fan housing develops a leak, you don’t want it releasing concentrated radon into a room you occupy.
After installation, the contractor places a U-tube manometer (a small, liquid-filled gauge) on the pipe. This simple device lets you visually confirm the system is creating suction every time you glance at it. If the liquid levels are uneven, the system is working. If they’re level, something is wrong.
Keeping Your System Working
Radon fans typically last 5 to 10 years before needing replacement. A healthy fan produces a steady, predictable hum. Watch for these signs of failure: grinding, rattling, or humming that changes over time; a warm fan housing or faint electrical smell; the manometer reading dropping or fluctuating; or the fan cycling on and off intermittently. Any of these signals that the motor is declining and replacement is needed soon.
Retest your home’s radon levels every two years, even with a working system, and always retest after any major renovation that affects your foundation, HVAC system, or basement layout. A system that worked perfectly for years can become less effective if new cracks develop or if changes to your home alter the pressure dynamics.