How Active Soil Depressurization Works
An active soil depressurization system is the mitigation method used for the large majority of homes with an elevated radon result. A pipe is routed from a suction point beneath the foundation to an in-line fan, which runs continuously to draw soil gas from underneath the home and vent it above the roofline, away from windows and other openings. The fan creates a zone of negative pressure beneath the slab or basement floor, so air is pulled downward and out through the pipe rather than seeping upward into the living space. This is different from simply sealing cracks: sealing alone rarely lowers a result enough on its own, because soil gas will generally find another path into the home if it isn't actively being redirected.
Suction Point Planning
Every installation starts with figuring out how many suction points a specific home needs, based on how easily air moves through the material beneath the slab. Clay-rich glacial till soils, common across the Bismarck-Mandan area, are generally less permeable than sandy or gravelly soil, which can mean a single suction point doesn't pull enough vacuum across the whole foundation footprint. In those cases, an installer may plan for an additional suction point or a stronger fan to move enough air. This is decided based on diagnostic testing of the specific foundation rather than applied as a one-size-fits-all default.
System Components
A typical system includes PVC piping routed through an unfinished area, closet, or exterior wall; an in-line radon fan, usually mounted in an attic, garage, or exterior location away from windows and living space; a U-tube manometer, a simple gauge that shows at a glance whether the fan is running; and an exterior discharge point that terminates above the roofline, positioned away from windows, doors, and areas where people spend time.
Sealing And Prep Work
Sealing major foundation openings — a sump pit lid, gaps at the floor-wall joint, and visible cracks — is a standard companion step to the suction system, not a replacement for it. A sealed sump pit or crack helps the system maintain pressure more efficiently across the whole foundation rather than losing suction to an easy opening near the suction point.
Installation Timeline And What To Expect
A straightforward basement or slab-on-grade home with a single suction point is often a one-day installation. Homes with a finished basement, a crawl space, or a mix of foundation types under one roofline typically take longer, since pipe routing has to preserve finished walls and ceilings and the crawl space membrane process adds its own steps. Sub-slab depressurization covers the suction-point planning process for basement and slab homes in more depth.
Winter Installation In North Dakota
Exterior routing, roofline penetration, and discharge placement can all be affected by frozen ground, snow load, and ice buildup during a North Dakota winter. Many systems are still installed through the colder months without issue, but scheduling and materials sometimes need to shift slightly for a winter job compared to a summer one, which is worth asking about directly when a project is time-sensitive.
Post-Installation Retesting
Once a system is running, a retest confirms whether the result has dropped below the EPA's 4 pCi/L action level. The manometer is a useful day-to-day indicator that the fan is operating, but a retest is the way to confirm the mitigation actually worked. Fans are generally rated to run for a number of years and can eventually need replacement, which is worth keeping in mind as part of a system's ongoing upkeep. See the cost guide for what affects installation pricing for a specific home.
Choosing A Discharge Location
The discharge point has to terminate above the roofline and stay clear of windows, doors, and any spot where discharged air could re-enter the home or drift toward an outdoor living space. On a Bismarck-area home, that also means accounting for snow shedding off the roof, ice buildup near the termination point, and keeping the pipe run clear of areas where a ladder or roof-clearing tool would need access during winter maintenance. Installers typically walk the exterior of the home before finalizing a route rather than defaulting to the shortest possible pipe run.
System Warranties And Long-Term Care
Most radon fans carry a manufacturer's warranty covering a set number of years, and installers commonly back their labor separately. Over the life of a system, the main upkeep is a periodic glance at the manometer to confirm the fan is still running, and eventually replacing the fan when it reaches the end of its service life. Homeowners who notice the manometer reading has changed, or who hear a new noise from the fan, should treat that as a signal to have the system checked rather than waiting for a scheduled retest to catch the issue.
Radon Mitigation Installation Questions
- How long does installation take?
- A straightforward basement or slab-on-grade installation is often completed in a single day; homes with crawl spaces, finished lower levels, or multiple foundation types can take longer.
- Will I be able to hear the fan running?
- Radon fans are designed to run quietly, and most homeowners report little to no noticeable noise once the fan is mounted in an attic, garage, or exterior location.
- Does the fan run all the time?
- Yes. Active soil depressurization systems run continuously to maintain negative pressure beneath the foundation, which is why the manometer is checked periodically to confirm the system is still operating.
- How do I know the system worked?
- A post-installation retest is the way to confirm the level has dropped below the EPA's 4 pCi/L action level; the manometer shows the system is running, but a retest confirms the result.
- Can a system be installed in winter?
- In many cases, yes, though frozen ground, snow load, and ice buildup can affect exterior routing and discharge placement, so winter jobs sometimes need slightly different scheduling or materials.