Does Radon Mitigation Really Work?

Yes — With One Important Caveat

Sub-slab depressurization (SSD) is one of the most effective environmental remediation techniques that exists for homes. The EPA, AARST, and independent researchers all confirm the same result: properly installed systems reduce radon by 90% or more in the vast majority of homes.

The caveat: "properly installed" is doing real work in that sentence. A system installed without a pre-installation communication test, with the wrong fan for the sub-slab conditions, or with unsealed penetrations will underperform. The technique works — the execution determines whether your specific system works.

What the Data Shows

The EPA's own analysis of thousands of post-mitigation tests found:

• Average reduction: 90%+ across all home types
• Homes below 4.0 pCi/L after mitigation: ~99% when the system is properly designed and installed
• Homes below 2.0 pCi/L after mitigation: ~85–90% (2.0 pCi/L is the WHO recommended action level)

For context: a home starting at 12 pCi/L typically ends up at 0.8–1.5 pCi/L after a properly installed system. A home at 40 pCi/L typically ends up at 2–4 pCi/L — occasionally requiring a second suction point to get below 4.0 pCi/L.

How It Works

The principle is simple: make the air pressure under your slab lower than the air pressure inside your home.

Radon moves from high pressure to low pressure. Before mitigation, the sub-slab zone is at roughly the same pressure as your basement — so radon drifts upward through cracks, penetrations, and porous concrete into your living space.

After a sub-slab depressurization system is installed, the fan creates a strong negative pressure zone beneath the slab. Radon is now being actively pulled away from your home rather than drifting into it. The fan vents this radon-laden air outside, above the roofline, where it disperses harmlessly into the atmosphere.

The physics don't care how high your starting level is. Whether you're at 5 pCi/L or 50 pCi/L, the same mechanism applies — you may just need a higher-suction fan or more suction points at extreme levels.

Why Some Systems Underperform

Wrong fan for the conditions. Sub-slab soil type matters enormously. Loose gravel communicates well — a standard XP201 fan creates suction across a large area. Packed clay communicates poorly — suction doesn't travel far, and you may need a higher-suction fan (GX3 or GX5) or additional suction points.

Unsealed penetrations. Every crack, gap, floor drain rim, and utility penetration in the slab is a path for radon to bypass the system. A properly installed system seals all visible entry points in addition to installing the fan.

Open sump pit. An unsealed sump pit is the biggest single bypass in most basements. Even a good fan works inefficiently if there's a direct open connection between the house and the soil.

Too many isolated sub-slab zones. Homes with additions, attached garages, or changes in foundation depth sometimes have isolated sub-slab sections that a single suction point doesn't reach.

Fan failure. A fan that's failed silently (no audible change, but the motor has stopped) lets levels creep back up over months. This is what the manometer is for — check it monthly.

What To Do If Your System Isn't Working

1. Check the manometer — confirm the fan is actually running and creating negative pressure. If levels are equal, the fan has failed.
2. Retest — use a fresh short-term kit. If you're still above 4.0 pCi/L, the system needs adjustment.
3. Have a certified mitigator assess — they can measure actual sub-slab depressurization at multiple points to identify whether coverage is adequate.
4. Add a suction point — most underperforming systems are solved by adding one additional suction hole in the isolated zone. This typically adds $200–$500 to the original job.
5. Upgrade the fan — if sub-slab pressure is marginal, a higher-suction GX3 or GX5 often solves the problem without adding a second hole.

The Bottom Line

Radon mitigation works. The EPA guarantees this — literally: any certified contractor who follows AARST-ANSI installation standards should be able to guarantee a result below 4.0 pCi/L or will remediate the system until it does. Ask for that guarantee in writing before work begins.

If your contractor doesn't offer a performance guarantee, find one who does.

Find a certified radon mitigator in your state →