How Does a Radon Mitigation System Work?

The Core Principle

Radon enters homes because indoor air pressure is slightly lower than soil gas pressure beneath the foundation. Soil gas — including radon — flows toward lower pressure, seeping in through cracks, floor-wall joints, and penetrations.

A radon mitigation system reverses this dynamic. Instead of the home being slightly negative relative to the soil, the soil is made strongly negative relative to everything else. Radon is pulled *away* from your home instead of into it.

The Components

1. Suction point(s)

A 3- or 4-inch hole is core-drilled through the foundation slab into the sub-slab aggregate (gravel layer beneath the concrete). This is where the system draws from. Most homes need 1–2 suction points; large or compartmentalized homes may need more.

2. PVC pipe

Schedule 40 PVC runs from the suction point, up through the home (often through a closet or garage wall), and exits above the roofline. The pipe routes must not terminate near windows, HVAC intakes, or areas where people spend time.

3. Radon fan

The continuously running fan — mounted in the attic, garage, or on the exterior — creates the negative pressure that drives the system. Common brands include RadonAway, Festa Radon Technologies, and Fantech. Fan selection depends on sub-slab aggregate type and the home's suction field extension.

4. Manometer

A U-tube liquid gauge mounted on the pipe shows whether the system is operating. If both columns are level, the fan has failed. A visible difference indicates the system is working. This is your daily "system check" — glance at it when you walk by.

5. Electrical connection

The fan requires a standard 120V outlet. Licensed contractors connect the fan through a dedicated circuit or tap an existing junction. Some systems use exterior-rated wiring runs.

What Happens to the Radon

The fan draws soil gas (including radon) from beneath the slab continuously. This gas travels up the pipe and exits above the roofline — typically 12+ inches above the roof surface and away from windows and HVAC intakes. At those concentrations and at that height, radon disperses harmlessly into outdoor air.

The system doesn't "destroy" radon. It relocates the exhaust point from inside your living space to outside, where natural dilution handles it.

For Crawl Space Homes

Crawl space radon mitigation works differently because there's no concrete slab to suction through. The standard approach:

Encapsulation + depressurization:

1. A heavy polyethylene vapor barrier (10–20 mil) is sealed over the crawl space floor and up the walls
2. A suction pipe is run through or under the liner
3. A fan draws soil gas from beneath the liner and exhausts outside

The liner prevents radon and moisture from entering the crawl space air. The fan ensures any gas that does penetrate has a directed exhaust path.

Why the Fan Runs Constantly

Some homeowners want to turn the fan off at night or when away. Don't.

Radon continuously decays and is continuously replenished from soil uranium. The moment the fan stops, sub-slab pressure equalizes, and radon starts migrating toward lower pressure — your home. Levels can rebuild to 50% of pre-mitigation within 8–12 hours with the fan off.

Radon fans are designed for 24/7 operation. Running continuously is normal and expected.

How Effective Is It?

A properly installed system by a certified contractor typically reduces indoor radon by 90%+. EPA data shows:

• Homes averaging 8 pCi/L typically reach 0.5–1.5 pCi/L post-mitigation
• Homes averaging 20+ pCi/L typically reach 1.0–2.5 pCi/L post-mitigation
• The EPA action level is 4.0 pCi/L; most systems bring homes well below 2.0 pCi/L

The main variable is sub-slab aggregate quality. Homes with good gravel beneath the slab achieve wide pressure field extension from a single suction point. Homes with tight soil or sand may need multiple points.

What Can Go Wrong

• Fan failure: The manometer goes flat. Fan replacement costs $300–$800 installed.
• Pipe blockage: Rare, but dirt intrusion can restrict airflow. Detectable by reduced manometer differential.
• New entry points: Major renovations that cut into the slab or add plumbing penetrations can create new radon pathways. Retest after significant foundation work.
• Incorrect installation: A pipe that terminates below the roofline or near a window re-exposes occupants. Always hire NRPP/NRSB certified contractors.

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