Sub-slab radon mitigation systems
A well-designed system stops radon before it gets inside. Here's how sub-slab depressurization works and what to ask about.
Most radon systems in Red River Valley homes use sub-slab depressurization. Instead of trying to clean radon out of indoor air, the system puts the soil under your floor at slightly lower pressure than the house, so the gas goes up the pipe and out above the roof instead of through the slab.
What gets installed?
- A hole cored through the basement floor, with a small pit dug out underneath to give the fan room to pull.
- PVC pipe from the pit, routed up through a closet, chase or garage to the attic, or out through the rim joist and up an outside wall.
- An inline radon fan in the attic, garage or outside, running continuously.
- A discharge above the roof line, placed away from windows, doors and other openings.
- Sealing of major cracks, the floor-wall joint where reachable, and the sump with an airtight cover.
- A pressure gauge, usually a U-tube manometer, so you can see at a glance that the fan is pulling.
Does the cold change the design?
It should. Exterior pipe and outdoor fans on a Grand Forks house deal with long stretches of subzero weather; the city's record low is minus 43 degrees. Warm, damp soil gas condenses in cold pipe, so installers slope the pipe to drain and think about where ice can form. Interior routes through a heated chase or the garage avoid some of that. Ask the installer how they handle condensation and frost on your house.
What's different in Minnesota?
In East Grand Forks and Crookston, the installer must be an MDH-licensed radon mitigation professional working for a licensed mitigation company. MDH requires an MDH tag on every professionally installed system, placed next to the pressure gauge, and a written operation, maintenance and monitoring plan for the owner. MDH also says the work must follow ANSI/AARST standards and that electrical work must meet Minnesota Department of Labor and Industry requirements.
How do I know it worked?
Test again after the system has been running. A short-term test is fine for this check. If the number is still high, a good installer will adjust the fan, seal more, or add a suction point. Ask how the post-install test will be done before you sign.
What drives the price?
- The size and shape of the foundation, and whether there's more than one section
- How well air moves through the fill under the slab
- Interior versus exterior pipe route
- Extras like a sump cover, crack sealing or a crawl space membrane
Pricing comes from the radon company once it knows your foundation and has usually seen the house in person. We don't quote prices, and any figure given over the phone is a rough starting point, not a bid.
Where we connect you with help
Common questions
Does the radon fan run all the time?
Yes. Radon fans are built to run nonstop. Glance at the manometer now and then to make sure it's still pulling.
Will an air purifier or dehumidifier lower radon?
Not reliably. Stopping radon at the foundation with a depressurization system is the proven fix.
Related services
More background: Red River Valley radon guide.
Radon kit came back over 4?
Call and a local radon mitigation company will look at your house and quote a system.