Radon Systems: What Homeowners Need to Know
When a test shows radon at or above the EPA action level of 4 pCi/L, a mitigation setup is the engineered answer. The category covers several designs, but they all share one job: capture radon-laden soil gas under your home and route it safely outside. Understanding how radon systems differ helps you ask the right questions before a contractor cuts into your slab. This guide summarizes EPA and CDC guidance current as of 2026; it is educational only and not a diagnosis, so consult a certified radon professional for testing and design decisions.
What are radon systems and how do they work?
A radon system is a network of piping, and usually a fan, that depressurizes the soil beneath your foundation so gas is pulled into a vent rather than seeping up through cracks. The most common design, sub-slab depressurization, draws suction from a pit cut into the floor slab. A pipe carries the captured gas up through the house or along an exterior wall and discharges it above the roofline, where it disperses harmlessly.
The principle is pressure. Soil under a home is often at slightly higher pressure than the indoor air, which drives radon inward, especially during Colorado winters when heated homes pull air upward. A radon system reverses that gradient by making the space under the slab the low-pressure zone, so gas flows into the pipe instead of into your basement. The EPA reports that a properly installed system can lower indoor radon by up to roughly 99 percent.
The main types of radon systems
Homeowners usually choose among a few designs based on foundation type and whether the home already tests high.
Active sub-slab depressurization
This is the workhorse retrofit for homes with a basement or slab-on-grade. A continuously running inline fan pulls soil gas from beneath the concrete and vents it above the roof. It is the most reliable way to bring an existing high reading below the action level, and it gives the installer measurable control over suction. The deeper overview of how a radon mitigation system works walks through the components.
Passive systems
A passive system uses no fan. It relies on the natural rise of warm air, the stack effect, to draw gas up the vent pipe. These are typically built into new construction and cost nothing to run, but they move less gas and may not get a high home under 4 pCi/L on their own. Many are designed so a fan can be added later, converting them to active.
Sub-membrane depressurization for crawl spaces
Homes with crawl spaces use a heavy sealed plastic membrane over the dirt floor, with suction drawn from beneath it. The membrane acts like the slab does in a basement system, giving the fan a sealed surface to depressurize. Mixed foundations sometimes combine this with sub-slab suction.
How a radon system actually moves the gas
The mechanics are worth understanding because they explain why some systems work and others fall short. Soil beneath a foundation is typically at slightly higher pressure than the air inside the home. That pressure difference, combined with the stack effect of warm air rising through a heated house, drives radon-laden soil gas upward through every available opening: cracks, the floor-wall joint, utility penetrations, even the pores of the concrete itself.
An active system reverses the gradient. By drawing suction from a pit beneath the slab, the fan makes the space under the foundation the lowest-pressure zone in the equation. Soil gas now flows toward the suction point and into the pipe rather than into the basement, because gases move from higher to lower pressure. The captured gas travels up the vent and discharges above the roofline, where it dilutes into the open atmosphere. The elegance of the design is that it does not try to seal out an invisible gas perfectly; it simply gives that gas an easier path out than in.
This is also why fan sizing and suction-point placement matter so much. If the fan cannot establish negative pressure across the entire slab, some areas keep leaking radon inward. Tight clay soils make that harder, which is why a competent installer tests the pressure field before committing to a single suction point.
Parts of a radon system and what each does
Most systems share a recognizable set of components. The suction point is the cored opening in the slab where gas is collected. The vent pipe, usually PVC, carries that gas up and out. The fan, mounted in an attic, garage, or on an exterior wall, provides the suction; it is sealed and runs around the clock. The manometer is the small U-tube gauge that shows whether the fan is pulling pressure; an offset in the liquid columns means it is working, while level columns signal a failure. Some installs add sealing at major slab cracks and the sump pit to improve suction, though sealing alone is not a substitute for active venting.
Fans are sized to the home. A tight, clay-heavy soil resists airflow and may need a stronger fan or more than one suction point, while a gravel-bedded slab pulls easily. Getting the sizing right is the difference between a system that holds below the action level and one that does not.
How installers choose the right system for a home
Selecting a system is a matter of reading the building, not applying a template. The foundation type is the first fork in the decision. A full basement or slab-on-grade home points toward sub-slab depressurization. A crawl space points toward sub-membrane depressurization. A mixed foundation, increasingly common in Front Range homes that combine a basement with a crawl-space addition, may need a hybrid that draws from both.
Soil permeability is the second factor. Before committing to a single suction point, a careful installer may run a pressure-field extension test, drilling a small test hole and measuring how far suction reaches from the proposed point. Loose, gravelly soils transmit pressure easily and often need only one suction point. Dense clay soils, which appear across much of the region, resist airflow and may require a stronger fan, a larger suction cavity, or more than one suction point to depressurize the whole slab evenly. Getting this right at the design stage avoids the frustration of a finished system that still tests high in one corner.
Pipe routing and discharge round out the design. The installer weighs interior routing, cleaner-looking but more invasive, against an exterior run that climbs the outside wall. Either way the discharge must clear the roof eave and stay away from windows so vented gas disperses rather than re-entering. The full picture is laid out in this guide on a radon mitigation system and its components.
What radon systems cost and what drives the price
The EPA’s general guidance puts most residential radon mitigation in a range running from several hundred dollars on the low end to well over a thousand on the higher end, with the typical job landing in the middle. Several variables move a quote within that band. Foundation type matters most: a simple open basement with gravel under the slab sits at the low end, while a finished basement, a crawl space, or a multi-foundation home costs more because of added labor and materials.
The number of suction points is the next big driver. A tight clay slab that needs two or three points to depressurize evenly costs more than a single-point system on permeable soil. Pipe routing factors in too, since concealing a run inside finished walls takes more time than an exterior climb. Local labor rates and the fan model selected complete the picture. Across all of these, the cheapest bid is rarely the best value. A system that fails to hold radon below 4 pCi/L solves nothing, so the right comparison is value and verified results, not the headline price.
How radon systems lower your health risk
Radon is the leading cause of lung cancer among nonsmokers in the United States, according to the EPA, and the second leading cause overall behind smoking. Risk rises with both the concentration and the years of exposure. Because radon is invisible and odorless, testing is the only way to know your level, and a system is the proven way to reduce it. The EPA sets 4 pCi/L as the action level and notes that any reduction lowers risk, with no level considered entirely risk-free.
Colorado’s geology makes this more than theoretical. Much of the Front Range, including Denver, Douglas, El Paso, Boulder, and Jefferson counties, falls into the EPA’s highest-potential zone. A working system is the most dependable long-term control. The broader radon testing guide for Front Range homeowners explains how to confirm you need one.
When a home needs a radon system at all
A system is the answer to a measured problem, not a default feature every home requires. The trigger is a test result at or above the EPA action level of 4 pCi/L. Below that, the EPA notes that risk still exists and that reducing exposure always lowers it, but the formal recommendation to install a system kicks in at 4 pCi/L. The only way to know your number is to test, since radon is invisible and odorless and gives no symptoms at any level.
For homes on the Front Range, the odds of an elevated reading are high enough that testing is strongly advised regardless of age or construction. Newer homes are not exempt; tight, energy-efficient construction can actually trap radon more effectively than a drafty older house. Real-estate transactions are a common moment for testing, since a buyer wants to know whether a system will be needed. If a short-term test during a sale reads high, a long-term test or a confirmed system becomes part of the negotiation. The point is that the decision to install rests on data, and the broader radon testing guide for Front Range homeowners walks through how to gather it correctly.
Maintaining and verifying your system
A radon system is low-maintenance but not no-maintenance. Check the manometer every month or two; even liquid columns mean the fan has stopped and radon may be climbing. The fan runs continuously and typically lasts five to ten years before it needs replacement. There are no filters to change and no lubrication to add.
Verification is the part homeowners skip most. After installation, and after any fan replacement, retest to confirm levels are below 4 pCi/L. A short-term test gives a fast read; a long-term test over more than ninety days reflects your true year-round average, which is especially relevant in Colorado where months of sealed, heated air concentrate radon. The EPA recommends retesting every two years even with a working system, and again after major foundation or remodeling work that could change how soil gas moves under the slab.
Common problems and how systems are kept reliable
Even a well-built radon system can run into issues over its life, and knowing the warning signs helps homeowners catch them early. The most common failure is the fan itself, which runs around the clock and typically lasts five to ten years before the motor wears out. A silent or rattling fan, or a manometer that has drifted to level, signals it is time for a replacement. Because the fan is sealed and lubricant-free, it is swapped rather than repaired.
Other problems are subtler. A cracked or disconnected pipe joint can leak suction and let radon back indoors. Ice forming inside an exterior fan during a hard Colorado freeze can briefly choke airflow. Condensation pooling in a fan mounted off-vertical strains the motor and shortens its life. New cracks in the slab, or a basement remodel that opens fresh pathways for soil gas, can raise readings even with the original fan still spinning. None of these announce themselves through smell or sound, which is why routine retesting is the backstop.
Keeping a system reliable comes down to a short list of habits. Check the manometer every month or two. Note the fan’s installation date so you know when to expect end of life. Retest every two years and after any work that disturbs the foundation. Label the system so a future homeowner understands what it is. These small steps keep a radon system doing its one job, holding the air below the action level, for the long haul. For homeowners weighing whether they even need a system yet, the broader radon testing guide for Front Range homeowners covers how to confirm the starting level.
References
- Consumer’s Guide to Radon Reduction — U.S. Environmental Protection Agency
- Health Risk of Radon — U.S. Environmental Protection Agency
- About Radon — Centers for Disease Control and Prevention
Front Range homeowners weighing a new system or unsure if an existing one still works can get connected with a vetted local mitigation pro. Get in touch through our contact page to start.