Home › Radon mitigation systems

Radon Mitigation Systems: How Sub-Slab Depressurization Works

Updated November 1, 2026 · General information, not medical advice

Some links on this page are affiliate links. If you buy through them we may earn a commission at no extra cost to you. How we make money.

The short answer: Most radon mitigation systems are a pipe and a fan. The pipe goes through the floor into the soil or gravel under the house. The fan pulls radon from under the house and vents it above the roof. EPA calls this active subslab suction (also called sub-slab depressurization) and says it is the most common and usually the most reliable method.

Not medical advice. This page repeats EPA and CDC guidance in plain words. Follow your state radon program and a certified radon professional for decisions about your home, and talk to a doctor about health concerns.

How a sub-slab system works

A contractor inserts one or more suction pipes through the floor slab into the crushed rock or soil underneath. EPA says often only a single suction point is needed.
A radon vent fan connected to the pipes draws radon gas from below the home and releases it into the outdoor air.
The fan also creates a negative pressure, or vacuum, under the slab, so radon is pulled away instead of entering the living space.

EPA says these systems do not require major changes to your home. Similar systems can be installed in homes with crawl spaces.

What your system should have (EPA's checklist)

A warning device that alerts you if the system stops working, such as a liquid gauge, sound alarm, light or dial. It must be where you can see or hear it.
Clear labels so nobody changes the system by accident.
The exhaust pipe must vent above the roof surface and 10 feet or more above the ground. It must be 10 feet or more from windows, doors or other openings, unless it vents at least 2 feet above them.
The fan must not be in or below a livable area. Common places are attics, garages and the outside of the home. Outdoor fans must meet local building codes for exterior use.
Electrical connections must follow local electrical codes. North Carolina's radon program notes that adding or changing wiring usually requires a licensed electrician.

Other types of systems

Foundation	Method EPA describes
Basement or slab-on-grade	Soil suction: subslab suction (most common), drain-tile suction, sump-hole suction or block-wall suction.
Crawl space	Submembrane suction: a high-density plastic sheet over the dirt floor, with a vent pipe and fan. EPA calls it the most effective way to reduce radon in crawl space homes when properly applied.
New construction	Passive subslab suction, which relies on natural air movement instead of a fan. EPA says it is generally not as effective at high levels. If a new home tests at 4 pCi/L or higher, a vent fan can be added to make it active.

Source: EPA, Consumer's Guide to Radon Reduction and Home Buyer's and Seller's Guide to Radon. Homes with more than one foundation type may need a combination.

What does not work well on its own

Sealing cracks alone. EPA does not recommend it.
Opening windows. It helps briefly; EPA says levels usually return within about 12 hours of closing up.

After the system is in

Test again. EPA says to test within 30 days of installation, no sooner than 24 hours after the fan is running. It recommends an independent follow-up test to avoid conflict of interest.
Watch the warning device, and call a contractor if it shows a problem.
Retest every two years, EPA says, to be sure levels stay low.
Expect small running costs. EPA says fan systems slightly increase your electric bill and can cause some loss of heated or cooled air. Michigan's EGLE says the average operating cost is about $3 a month and that fans last around 11 years; Utah's DEQ gives about $8 to $10 a month and about 15 years. Both are state estimates, so yours may differ. See radon mitigation cost.

High result? Get more than one estimate.

EPA says to hire a qualified, certified radon mitigation contractor and to get more than one estimate. Start with your state radon program, then compare written quotes.

How to find a certified contractor Compare local radon pros

Common questions

What is sub-slab depressurization?

It is the most common radon fix. EPA calls it active subslab suction. Pipes go through the floor slab into the crushed rock or soil below, and a fan pulls the radon from under the house and releases it outdoors above the home. It also creates a vacuum under the slab.

How much can a radon system reduce radon?

EPA says some radon reduction systems can reduce levels in your home by up to 99 percent, and that most homes today can be reduced to 2 pCi/L or below.

Is sealing cracks enough?

No. EPA does not recommend sealing alone. It says sealing by itself has not been shown to lower radon levels significantly or consistently. Sealing is a basic part of most approaches, because it makes other methods work better.

Can I open windows instead?

Only as a temporary measure. EPA says radon levels most often return to previous values within about 12 hours after windows, doors and vents are closed, and that open windows bring loss of conditioned air, higher costs and security concerns.

Can I install a radon system myself?

EPA recommends a qualified radon mitigation contractor, because without the proper equipment or technical knowledge you could actually increase your radon level or create other hazards. If you are thinking about doing it yourself, EPA says to contact your state radon office first for guidance and training information.

Related guides

Sources

Free printable: Radon Test Day Checklist

EPA's testing steps in one page, plus what your result means. Download the one-page PDF now, or get it by email along with a short series of five helpful emails.

Download the PDF