Radon mitigation systems
A well-designed system stops radon at the foundation instead of trying to clean it out of the air. Here's how it works in a Billings house.
Most systems in basement and slab homes use sub-slab depressurization, also called active soil depressurization. A fan creates a slight vacuum under the floor, so soil gas flows into a pipe and out above the roof rather than up into the house. Air purifiers and dehumidifiers don't do this job.
What gets installed?
- A suction point. The installer cores a hole through the slab and removes some fill to make a small pit under it. Before choosing a spot, many installers run a quick test to see how well air moves under the slab.
- The pipe. PVC runs from the pit either up through a closet or the garage into the attic, or out through a rim joist and up the outside wall.
- The fan. An inline radon fan sits in the attic, garage or outdoors, never in the living space or basement, and runs around the clock.
- The discharge. The pipe exhausts above the roof edge, away from windows, doors and neighbors' openings.
- Sealing. Accessible cracks, the floor-wall joint and the sump get sealed so the fan isn't pulling house air.
- A gauge and label. A U-tube manometer on the pipe shows suction, and the system should be labeled.
Inside or outside pipe in a Montana winter?
An interior route through the garage or a closet to the attic keeps the pipe out of sight and out of the worst cold. An exterior route can be simpler to install, but on below-zero nights the moisture in soil gas can condense and freeze at the outlet or in the fan. Installers who work here plan for that with pipe sizing, slope and fan placement. Ask how yours will handle it.
What else might the house need?
- A sealed, airtight lid on an open sump basin.
- More than one suction point when the soil under the slab is tight or the foundation has separate sections.
- A sealed membrane over any dirt-floor crawl space. See crawl space radon.
- An electrical outlet or circuit near the fan location.
How do I know it's working?
Test after it's installed, ideally with an independent tester, as Montana DEQ recommends. Look at the manometer now and then: uneven liquid means the fan is pulling. Then retest at least every two years.
What changes the price?
- Foundation type and size
- Interior versus exterior pipe route
- Number of suction points
- Add-ons like sump lids, sealing or a crawl space membrane
The radon company sets the price after it learns about your house, and usually after someone has looked at the foundation. We don't quote prices, and a number given over the phone is only a rough starting point.
Where we connect you with help
Common questions
How low will a system bring my radon?
It depends on the house, but a properly designed sub-slab system commonly brings levels well under 4 pCi/L. The follow-up test tells you your actual number.
Will the fan freeze in winter?
A system planned for Montana cold shouldn't stop working, but condensation can freeze in a poorly placed exterior run. Ask the installer how the pipe and fan are set up for subzero weather.
Related services
- Radon testing
- Crawl space and slab radon
- Radon for home buyers and sellers
- Radon fan replacement and repair
More background: Montana radon guide.
Got a radon number you don't like?
Call now and a local radon mitigation company will look at your house and quote a system.