How Does a Radon Mitigation System Work?

If your home has tested above the EPA action level — or if you are simply trying to understand what your options are before you test — knowing how a radon mitigation system actually works takes a lot of the mystery out of the process. Most homeowners picture something complicated, expensive, or disruptive. The reality is more straightforward. Modern radon mitigation is a well-established technology with a clear operating principle, and understanding that principle helps you appreciate both why it works and why it works so reliably.

The Core Problem the System Solves

To understand how mitigation works, it helps to recall what drives radon into a home in the first place. As we covered in our post on radon entry points, your home sits at a slightly lower air pressure than the soil beneath it. That pressure difference causes your home to draw soil air — and the radon it contains — upward through any available opening in the foundation. The home is essentially acting like a vacuum pulling from the ground below.

A mitigation system does not try to seal every crack and gap in the foundation — an approach that is both impractical and ineffective on its own. Instead it addresses the underlying pressure dynamic directly. It reverses the relationship between your home and the soil beneath it, so that instead of your home drawing radon in, the system is actively pulling radon away from the foundation before it ever has a chance to enter your living space.

Sub-Slab Depressurization: The Standard Approach

The most common and most effective radon mitigation method is called sub-slab depressurization, or SSD. The name describes exactly what it does: it creates a zone of negative pressure beneath the concrete slab of your foundation, depressurizing the soil so that radon moves toward the system rather than toward your home.

Here is how it is installed and how it operates:

A small hole — typically three to four inches in diameter — is core-drilled through the concrete floor of the basement or lowest level of the home. Through this hole, a suction pit is created in the aggregate or soil beneath the slab. This is the point where the system connects to the space beneath your foundation.

A PVC pipe is inserted into this suction point and routed through the home — typically running up through the interior or along an exterior wall — and exits above the roofline. The routing path varies depending on the layout of the home and what makes the most practical and aesthetically clean installation, but the destination is always outside and above the living space.

At a key point along this pipe, a radon mitigation fan is installed. This fan runs continuously, creating suction at the point beneath your slab and drawing radon-laden soil air up through the pipe and out above your roofline, where it disperses harmlessly into the outdoor air. Once the system is operating, the pressure beneath your slab is lower than the pressure inside your home — the opposite of the condition that was pulling radon in. Radon follows the path of least resistance toward the suction point rather than through your foundation into your living space.

What the Fan Does and Why It Matters

The fan is the active heart of the system. It runs around the clock, every day, maintaining the pressure differential that keeps radon moving away from your home rather than into it. Because it operates continuously, fan quality and reliability matter enormously — a fan that fails or underperforms compromises the entire system.

Good mitigation fans are designed for continuous operation over many years. They are energy efficient, relatively quiet, and built to handle the conditions of moving soil air consistently over a long service life. The difference between a quality fan and a cheaper alternative shows up not at installation but over time, in how consistently the system performs and how long it operates before needing attention.

The fan is typically installed in an unconditioned space — an attic, a garage, or on the exterior of the home — rather than in the living area. This placement keeps any slight fan noise out of the spaces where your family spends time and ensures that if there were ever any issue with the fan or the pipe, it would not affect the air inside the home.

The Diagnostic Indicator

A properly installed mitigation system includes a visual diagnostic tool called a manometer — a simple U-shaped tube filled with colored liquid that is mounted on the visible portion of the pipe inside the home. The manometer shows at a glance whether the system is operating correctly. When the fan is running and creating suction, the liquid in the manometer is displaced to one side. If the liquid is level — indicating no pressure differential — the system is not functioning properly and needs attention.

The manometer is your ongoing verification that the system is doing its job without requiring any active monitoring on your part. A quick glance tells you everything you need to know.

Variations for Different Home Types

Sub-slab depressurization is the standard approach for homes with poured concrete or block foundations and a basement or slab-on-grade construction. But not every home fits that profile, and mitigation approaches adapt accordingly.

Homes with crawlspaces use a variation called sub-membrane depressurization. Rather than drawing from beneath a concrete slab, the system draws from beneath a plastic sheeting membrane that is laid across the exposed soil of the crawlspace. The operating principle is identical — create negative pressure beneath the membrane so radon moves toward the system rather than into the home above.

Homes with multiple foundation types — part basement, part crawlspace, or part slab — may require a system with multiple suction points to address all of the relevant areas effectively. The number of suction points needed depends on the specific characteristics of the foundation and how well the sub-slab or sub-membrane communication allows the suction to reach across the full area.

What the System Does Not Do

A radon mitigation system is not an air purifier, a ventilation system, or a whole-home air quality device. It does one specific thing: it removes radon from beneath your foundation before it enters your home. It does not filter the air inside your home, it does not address other indoor air quality concerns, and it does not require any changes to how you heat, cool, or ventilate your living space. It operates quietly in the background, doing a single job very well.

Understanding what the system is designed to do — and what it is not designed to do — helps set accurate expectations for what life looks like after installation.

The Result

A properly designed and installed sub-slab depressurization system reduces radon levels dramatically in the vast majority of homes. The goal is not simply to get below 4 pCi/L — it is to bring levels as low as reasonably achievable, ideally approaching the low background levels found in outdoor air. Post-installation testing confirms that the system is performing as designed and gives you a verified number to replace the elevated result that prompted the work.

At All Michigan Mitigation, designing and installing radon mitigation systems is the work we do every day. We assess each home individually, determine the right approach for its specific foundation type and layout, and install systems built to perform reliably for the long term.

Visit us at allmichiganmitigation.com to learn more or to schedule a consultation about what mitigation would look like for your home.

All Michigan Mitigation is a West Michigan radon testing and mitigation company dedicated exclusively to helping homeowners understand and eliminate radon risk in their homes.