A radon mitigation system is simple to describe. It creates slightly lower air pressure under your home than inside it, so soil gas gets pulled into a pipe and blown outside instead of seeping into your rooms.
Sub-slab depressurization (the standard system)
The EPA says active sub-slab suction (also called sub-slab depressurization, or SSD) is the most common and usually the most reliable method [EPA-3]. Here’s how it fits together:
- Suction point: the installer drills a hole (usually 4–6 inches) through the basement floor or slab and digs out a small pit underneath. This gives the fan more area to pull from.
- Pipe: a sealed PVC pipe runs from that hole up through the house (closet, chase, garage, attic) or along the outside wall.
- Fan: a radon fan on the pipe runs non-stop. The EPA says it must sit outside the living space, for example in an attic, garage or outdoors, and never in or below a lived-in area [EPA-3].
- Exhaust: the pipe vents radon above the roof edge, away from windows and other openings [EPA-3].
- Sealing: major cracks, gaps around pipes and the sump pit are sealed so the fan isn’t pulling house air [EPA-3].
- Monitor: a pressure gauge (usually a U-tube manometer) on the pipe shows the system is pulling. An alarm is optional.
Often one suction point is enough. Homes with dense soil under the slab, or with several foundation sections, may need more [EPA-3].
Variations for other foundations
- Drain-tile suction: uses existing drain tiles around the foundation as the collection path [EPA-3].
- Sump-hole suction: the sump pit gets an airtight lid and becomes the suction point [EPA-3].
- Block-wall suction: pulls radon from the hollow cores of concrete block walls [EPA-3].
- Crawl spaces: the EPA’s preferred method is sub-membrane suction: heavy plastic sheeting goes over the dirt floor, sealed at the seams and walls, and a pipe and fan draw radon from beneath it. Fan-ventilating the crawl space itself is a less favored option that can raise energy costs and risks backdrafting [EPA-3].
- Passive systems: new homes are sometimes built with a pipe but no fan. These are generally less effective at high levels, but you can usually “activate” one by adding a fan. Colorado’s health department puts that at about $500 [EPA-3][CO-1].
What the job usually looks like
- Many installers start with a short visual inspection, and some do diagnostic suction tests to see how well air moves under the slab [EPA-3].
- Most single-family installs take about a day. (This is a typical figure, not from a cited source, so confirm with your installer.)
- After installation the EPA recommends a post-mitigation test within 30 days, but no sooner than 24 hours after the system starts. A 2–7 day test is enough, under closed-house conditions [EPA-3].
- Pennsylvania rules require a post-mitigation test of at least 48 hours [PA-6]. Ohio’s health department says the contractor must perform a post-mitigation test [OH-1].
- Ask for a written explanation of the system, maintenance instructions and warranty copies [EPA-3].
Living with a system
- Don’t turn the fan off. It has to run continuously to work [EPA-3].
- Check the gauge regularly. If the liquid levels in the U-tube are even, the fan may have stopped.
- Expect a fan replacement eventually. The EPA says fans may last five years or more [EPA-3].
- Retest at least every two years, and after remodeling a basement or making big changes to the house [EPA-3][OH-1].
Does it work?
The EPA says some systems reduce radon by up to 99% [EPA-3]. RadonCosts’s homeowner reports show real before-and-after readings by foundation type. See reports or add yours.
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