How Radon Mitigation Systems Work: A Complete Guide

A radon mitigation system creates negative pressure beneath your foundation to redirect radon gas before it enters your home. Most residential systems cost $800 to $2,500 and take one day to install. Here is exactly how they work.

How Sub-Slab Depressurization Works

Sub-slab depressurization (SSD) is the most widely installed radon mitigation method. It accounts for the vast majority of residential radon systems, and for good reason: it is simple, reliable, and effective at reducing radon levels by 80% to 99%.

The process starts with a single hole drilled through your basement slab or slab-on-grade foundation. The hole is typically 4 to 5 inches in diameter and goes straight through the concrete into the aggregate or soil beneath. A technician then excavates a small pit below the slab, roughly the size of a five-gallon bucket. This pit serves as the collection point where radon gas accumulates before being drawn upward.

A section of 3- or 4-inch Schedule 40 PVC pipe is inserted through the hole and sealed to the slab with polyurethane caulk. From there, the pipe is routed vertically through the home, typically through a closet, utility chase, or along an exterior wall. It exits the home and continues up past the roofline.

The critical component is the inline radon fan mounted along this pipe run, usually in the attic or on an exterior wall. This fan runs continuously, 24 hours a day, 365 days a year. It draws between 20 and 90 watts of electricity (comparable to a light bulb) and creates constant negative pressure beneath the slab. That negative pressure is the key: it reverses the natural pressure gradient that would otherwise pull radon up through cracks and openings in your foundation.

With the fan running, soil gases beneath your slab are pulled into the suction pit, up through the PVC pipe, and discharged above the roofline where they dissipate harmlessly into the outdoor air. Radon that would have seeped into your basement is intercepted before it ever crosses the slab. The air inside your home stays clean because the system captures the gas at its source.

A U-tube manometer (a simple liquid gauge) is mounted on the pipe inside the home so you can visually confirm the system is working. When the liquid levels in the two sides of the tube are uneven, the fan is creating suction. If the levels are equal, the fan has stopped and needs attention.

Types of Radon Mitigation Systems

Active Sub-Slab Depressurization (ASD)

This is the standard system described above and the most common radon mitigation method in the United States. ASD works for homes with poured concrete basements and slab-on-grade foundations. The fan creates active suction beneath the slab, which is why the system works regardless of weather conditions, wind patterns, or seasonal pressure changes. ASD systems reduce radon by 80% to 99% and typically cost $800 to $2,500 depending on the home's layout and foundation type.

Sub-Membrane Depressurization (SMD)

Homes with dirt-floor crawl spaces cannot use sub-slab suction because there is no slab. Instead, a heavy-duty polyethylene membrane (typically 6 mil or thicker) is laid over the entire crawl space floor and sealed to the foundation walls. A suction pipe penetrates the membrane and connects to an inline fan, creating negative pressure beneath the sheeting. Radon collects under the membrane and is vented through the pipe to above the roofline. SMD is equally effective as ASD when installed correctly and typically costs $1,000 to $2,800 because of the labor involved in sealing the membrane.

Block Wall Suction

Older homes built with hollow concrete block (cinder block) foundations face a unique problem: radon can enter through the hollow cavities inside the blocks themselves. Block wall suction targets this pathway by inserting a suction pipe into the hollow cores of the block wall, typically at the lowest course above the footing. The fan draws air from inside the block cavities, depressurizing them so radon vents upward through the pipe instead of leaking into the basement. This method is often used in combination with sub-slab depressurization for homes where both pathways contribute to elevated radon levels.

Heat Recovery Ventilator (HRV)

An HRV increases the rate of air exchange in your home, diluting indoor radon by bringing in fresh outdoor air. To avoid massive energy losses, the unit passes outgoing warm air and incoming cold air through a heat exchanger, recovering 70% to 80% of the thermal energy. HRV systems cost $1,500 to $3,500 installed and can reduce radon levels by 25% to 50%. They are not a primary radon solution for high levels but work well as a supplementary measure alongside depressurization. HRVs also improve overall indoor air quality by reducing humidity, volatile organic compounds, and stale air.

Passive Radon Systems

Since the early 2000s, many building codes require new homes to include radon-resistant construction features. A passive radon system consists of a PVC pipe running from a gravel layer beneath the slab up through the house and out the roof. There is no fan. The system relies on the natural stack effect (warm air rising) and wind pressure at the rooftop to draw soil gases upward.

Passive systems reduce radon by roughly 30% to 70%, which is enough for many homes. If post-construction testing shows radon above 4 pCi/L, the passive system can be activated by adding an inline fan to the existing pipe. This conversion costs $400 to $800 and instantly upgrades the system to full active depressurization performance.

System Components

Every active radon mitigation system uses the same core components:

Suction point: A 4- to 5-inch hole drilled through the slab with a small excavated pit beneath. Some homes require multiple suction points if the sub-slab material is tightly packed or the foundation footprint is large.
PVC pipe: 3- or 4-inch Schedule 40 PVC is the industry standard. The pipe runs from the suction point through the home and exits above the roofline. Exterior pipe runs are common when interior routing is impractical.
Inline radon fan: The fan mounts on the pipe, typically in the attic or on an exterior wall, and runs continuously. Radon fans draw 20 to 90 watts and are designed for years of uninterrupted operation. Common brands include RadonAway, Festa, and Fantech.
Manometer: A U-tube liquid gauge mounted on the pipe inside the home. It provides a visual confirmation that the fan is creating suction. A quick glance at the manometer tells you the system is working.
Foundation sealant: Polyurethane caulk and expanding foam are used to seal visible cracks in the slab, gaps around plumbing penetrations, and the joint where the slab meets the foundation wall. Sealing reduces the volume of air the fan must move and improves system efficiency.
Discharge point: The pipe terminates above the roofline, at least 10 inches above the roof surface and 10 feet from any window or opening, per EPA guidance. This ensures radon disperses into the atmosphere rather than re-entering the home.

The Installation Process

A typical radon mitigation installation takes 4 to 8 hours. Here is what happens, step by step:

Inspection and planning. The installer examines your foundation type, identifies the best suction point location, and plans the pipe route. Factors include slab thickness, sub-slab material, existing plumbing, and attic access.
Drilling the suction point. A core drill cuts a 4- to 5-inch hole through the concrete slab. In basements, this is usually placed in an unfinished area or utility room.
Creating the suction pit. The installer excavates soil and aggregate from beneath the slab through the hole, creating a cavity roughly 12 inches in diameter. This pit allows air to flow freely beneath the slab toward the suction point.
Routing the pipe. PVC pipe is connected at the suction point and routed through the home to the roofline. The route may go through interior walls, closets, or up along the exterior of the home. Exterior runs are painted or covered to match the house.
Mounting the fan. The inline fan is installed on the pipe, either in the attic (most common) or on an exterior wall above the first floor. Attic mounting keeps the fan out of sight and reduces any noise inside the home. The fan must be placed above the living space so that any pipe connections on the pressurized side of the fan (above the fan) are outside the home envelope.
Sealing the foundation. All visible cracks, gaps, and penetrations in the slab are sealed with polyurethane caulk or foam. The gap around the suction pipe is sealed to the slab. Sump pits receive airtight covers.
Installing the manometer. A U-tube gauge is mounted on the pipe at eye level, giving you a quick way to verify the system is running.
Post-installation testing. After the system runs for 24 to 48 hours, a radon test is performed to confirm the system has reduced levels below 4 pCi/L. Most installers include this test in their price or offer it as an add-on.

How Much Does Radon Mitigation Cost?

The total cost depends on your foundation type, system requirements, and local labor rates. Here are typical price ranges by system type:

System Type	Typical Cost	Best For
Active Sub-Slab Depressurization (ASD)	$800 to $2,500	Basements, slab-on-grade
Sub-Membrane Depressurization (SMD)	$1,000 to $2,800	Crawl spaces
Block Wall Suction	$800 to $2,500	Hollow block foundations
Heat Recovery Ventilator (HRV)	$1,500 to $3,500	Supplementary ventilation
Passive to Active Conversion	$400 to $800	New construction with passive pipe

Several factors push costs toward the higher end of these ranges:

Foundation type. Homes with both a basement and a crawl space may need two suction points or a combination of ASD and SMD, adding $500 to $1,000.
Home size and layout. Larger footprints or complex foundation shapes may require multiple suction points. Each additional point adds $300 to $600.
Pipe routing. If the pipe must run through finished living space, the installer needs to conceal it in walls or soffits, increasing labor time and cost.
Geographic location. Labor rates vary significantly by region. Installations in high-cost metro areas can run 20% to 40% more than the national average.
Accessibility. Tight crawl spaces, limited attic access, or unusual foundation configurations add labor hours.

Most radon mitigation companies offer free or low-cost estimates. Get quotes from two or three NRPP- or NRSB-certified professionals before choosing an installer.

Effectiveness and Maintenance

A properly installed active depressurization system reduces radon levels by 80% to 99%. Homes with pre-mitigation levels of 10 to 20 pCi/L routinely drop below 2 pCi/L after installation. The system begins working the moment the fan turns on, and a confirmation test within 24 to 48 hours verifies the reduction.

Ongoing maintenance is minimal:

Check the manometer monthly. A quick visual check confirms the fan is running and creating suction. If the liquid levels are equal, the fan may have failed.
Retest radon levels every 2 years. Home settling, new cracks, or changes in soil conditions can affect performance over time. A follow-up test ensures your levels remain below 4 pCi/L.
Replace the fan when it fails. Radon fans are built to run continuously and typically last 5 to 10 years. Replacement costs $200 to $400 including the fan and labor. Some fans have manufacturer warranties of 5 years.
Annual electricity cost. A radon fan drawing 20 to 90 watts costs approximately $40 to $80 per year in electricity, depending on your local utility rate and fan size.
Listen for changes. A radon fan that suddenly gets louder or quieter may be failing. Bearing noise (grinding or rattling) is the most common sign of a fan nearing end of life.

There are no filters to change, no annual service visits required, and no consumables to buy. A radon mitigation system is one of the lowest-maintenance home improvement investments you can make.

Take Action

If your home has tested at 4 pCi/L or above, radon mitigation is the proven fix. The system is straightforward, the installation is fast, and the results are measurable within days.

Find a certified radon mitigation professional in your area to get a free estimate and protect your household from radon exposure.

Frequently Asked Questions

How does radon mitigation work?

The most common method, active sub-slab depressurization, uses a continuously running fan connected to PVC piping that extends through your foundation. The fan creates negative pressure beneath the slab, pulling radon from the soil and venting it above the roofline before it can enter your home.

How much does radon mitigation cost?

Most residential radon mitigation systems cost $800 to $2,500 installed. The exact price depends on your foundation type, home size, pipe routing, and local labor rates. Homes with crawl spaces or complex foundations may cost $1,000 to $2,800. Converting an existing passive system to active costs $400 to $800.

How long does radon mitigation take?

A typical installation takes 4 to 8 hours and is completed in a single day. After installation, the system runs for 24 to 48 hours before a confirmation radon test is performed to verify the reduction.

How effective are radon mitigation systems?

Active depressurization systems reduce radon levels by 80% to 99%. A home with a pre-mitigation level of 20 pCi/L can typically be brought below 2 pCi/L. The system begins working immediately when the fan is turned on.

What maintenance does a radon system need?

Check the manometer (pressure gauge) monthly to confirm the fan is running. Retest radon levels every 2 years. The fan lasts 5 to 10 years and costs $200 to $400 to replace. Annual electricity runs $40 to $80. There are no filters or consumables.