How a radon mitigation system works
A radon mitigation system is a pipe and fan that pull radon-laden air from the soil under your foundation and vent it above the roof before it can get inside. The most common type is sub-slab depressurization. A gauge on the pipe (a manometer) shows the fan is working, and a follow-up test proves the level dropped. A quality system may bring year-round levels below 2 pCi/L.
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How the system works
Radon comes from the soil under your house. A mitigation system doesn't filter it out of the air. It stops it from getting in by making the soil under the floor a lower-pressure zone than the house, so gas flows into a pipe instead of up through cracks.1
- Vents above the roofline
- Fan in the attic, garage or outside
- Manometer shows the fan is pulling
- Cracks and gaps sealed
- Suction pit under the slab
- Soil gas is pulled into the pipe instead of up into the house
- Suction pit. The installer drills through the slab and digs out a small pit of soil underneath.
- Pipe. PVC pipe runs from the pit up through the house or along an outside wall.
- Fan. An inline fan, outside the living space, pulls air from under the slab around the clock.1
- Vent. The pipe ends above the roofline, away from windows, where radon disperses.
- Sealing. Major cracks, gaps and the sump pit are sealed so the fan pulls from the soil, not the basement.1
- Manometer. A U-tube gauge on the pipe shows the fan is working.1
“Sub-slab depressurization is the most common and usually the most reliable radon mitigation method.”
Massachusetts Department of Public Health
Types of systems
| System | Used for |
|---|---|
| Sub-slab depressurization | Homes with a basement or slab floor. The most common method.2 |
| Sub-membrane depressurization | Crawl spaces. A sealed plastic sheet covers the dirt floor and the pipe pulls from under it. |
| Drain-tile or sump suction | Homes with drain tile around the foundation or a sump pit that can be sealed and used as the suction point. |
| Block-wall suction | Hollow block foundation walls that let radon in through the cores. |
Many homes need a combination, especially when a basement sits next to a crawl space or a slab addition.
What results to expect
“A quality radon mitigation system may reduce year-round levels to below 2 pCi/L.”
Minnesota Department of Health
The only way to know is to test after installation. The CDC says to "test radon levels again after any repairs to be sure they worked."3
Living with a system
- Check the manometer every few months. Uneven liquid means the fan is pulling.
- Never switch off the fan. It only works while it runs.
- Retest every couple of years and after major renovations.
- Plan for a fan replacement someday. Fans run all the time and eventually wear out.
What it costs
Most systems cost $1,200 to $2,000 according to Massachusetts public health officials.2 Use the checker below to see how your quote compares and what to ask about.
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Common questions
How does a radon mitigation system work?
A fan creates suction under the foundation through a pipe set into a small pit dug below the slab. Soil gas, including radon, flows into the pipe instead of into the house and is vented above the roofline.
How do I know my radon system is working?
Look at the manometer, a U-tube gauge on the pipe. If the liquid levels are uneven, the fan is pulling. If they're even, the fan may have stopped. Retest your home every couple of years too.
Can I turn off my radon fan?
No. The system only works while the fan runs. When it stops, radon levels climb back up.
Will sealing cracks alone fix radon?
Rarely. Sealing helps the fan work better, but on its own it usually doesn't lower radon enough.
Where does the fan go?
Outside the living space: in the attic, the garage, or on an exterior wall. That way any leak in the fan or pipe on the pressurized side doesn't push radon into rooms you use.
Sources
- Radon Mitigation Systems Minnesota Department of Health
- Fixing Radon in Your Home Massachusetts Department of Public Health
- About Radon CDC