What Is a Radon System: A Plain-Language Guide
Homeowners across Colorado often hear that a house “has a radon system” or “needs one,” yet the equipment itself stays mostly out of sight: a pipe in a closet, a fan in the attic, a small box on a wall. So what is a radon system, and how does a length of pipe and a quiet fan actually lower an invisible, radioactive gas to a safe level? This guide explains the parts of a radon system, how the most common design works, the difference between active and passive setups, and what installation typically involves. It summarizes EPA and Colorado health-department guidance current as of 2026 and is informational only; consult a certified professional for testing and mitigation decisions and a physician for health concerns.
What is a radon system?
A radon system, more formally a radon mitigation system, is a set of components that captures radon gas before it enters the living space and vents it safely above the roof. The most common type, sub-slab depressurization, draws radon-laden air from beneath the foundation and exhausts it outdoors, lowering the indoor radon concentration to an acceptable level.
The system exists because radon is a naturally occurring radioactive gas that seeps up from soil and rock and can accumulate indoors. The EPA identifies radon as a leading cause of lung cancer, second only to smoking, which is why reducing elevated levels matters. Colorado sits in a region with widespread elevated radon potential, making these systems common across the Front Range. The full overview lives on the radon testing pillar, and the mechanics are expanded in the guide to how radon mitigation systems work.
How does a radon system work?
The principle behind sub-slab depressurization is straightforward: create a zone of lower air pressure beneath the slab than inside the home, so radon flows into the system rather than up through cracks in the floor.
A pipe penetrates the slab into the soil or gravel below. A fan, usually mounted in an attic or on the home’s exterior, pulls air from under the foundation through that pipe and pushes it up a vent stack that discharges above the roofline, where the radon disperses harmlessly. Because the area under the slab is now at slightly negative pressure relative to the home, soil gas takes the path of least resistance into the pipe instead of leaking into the basement. Sealing visible foundation cracks and the sump pit improves the system’s efficiency by reducing competing air paths.
The parts of a radon system
A typical active radon system has a small number of well-defined components, each with a clear job.
Suction point and pipe
The system starts at a suction point cut through the slab, often near or in a sump pit, that taps the air space beneath the foundation. From there, PVC vent pipe routes the gas upward and outdoors.
The fan
An inline radon fan provides the suction that makes the system active. It runs continuously and is installed in an unconditioned space, such as an attic or outside the home, so that any leak in the pressurized section after the fan stays outside the living area. Fan selection and replacement are covered in the guide to radon mitigation fans.
The vent stack and monitor
The vent stack carries radon above the roofline for safe discharge. A manometer, a simple U-shaped pressure gauge mounted on the pipe, lets homeowners confirm at a glance that the fan is pulling suction and the system is working.
Active versus passive radon systems
Radon systems come in two basic types, and the difference is the fan.
A passive system uses the same pipe routing but relies on natural air movement, the stack effect, to draw soil gas up and out, with no fan. Passive systems are often roughed in during new construction and can reduce radon somewhat, but they are less reliable at hitting low target levels.
An active system adds the continuously running fan, which makes it far more effective and consistent. Many passive systems are later upgraded to active by adding a fan when post-construction testing shows levels remain elevated. The trade-offs are explored in the guide to a passive radon mitigation system.
What level does a radon system aim for?
Radon is measured in picocuries per liter of air. The EPA recommends taking action to reduce radon when indoor levels reach or exceed 4 picocuries per liter, and notes that any reduction below that lowers risk further, with no level being entirely free of risk.
A well-designed active system commonly brings elevated levels well below the action threshold, and many achieve readings of around 2 picocuries per liter or lower. The only way to confirm performance is testing after installation. A system is not “done” until a post-mitigation test verifies it reached the target, which is why testing bookends the entire process.
What does installing a radon system involve?
Professional installation is usually a one-day job for a typical home. The installer selects a suction point, cores through the slab, routes the vent pipe up through the home or along the exterior, mounts the fan in an attic or outside, and seals foundation openings to improve performance.
System cost for a standard Front Range home commonly falls in a low four-figure range, varying with foundation type, routing complexity, and whether the home has a basement, slab, or crawl space. Crawl-space homes often require a sealed membrane over the soil, which adds labor. The installation sequence and what to expect are detailed in the guide to radon installation.
How radon systems differ by foundation type
Not every home is built the same, and the radon system has to match the foundation. The design that works for a poured basement differs from the one needed for a crawl space or a slab-on-grade home.
Homes with a basement or slab foundation are the most straightforward. The suction point penetrates the concrete slab into the soil or aggregate below, and sub-slab depressurization works as intended because the slab acts as a barrier that the fan can depressurize beneath. Sealing cracks and the sump pit improves performance.
Crawl-space homes require a different approach. Because there is no continuous slab, the installer typically lays a sealed polyethylene membrane, sometimes called a sub-membrane system, over the exposed soil and draws air from beneath that membrane. This adds material and labor, which is why crawl-space mitigation often costs more. Homes with a mix of foundation types, common in additions and renovations, may need more than one suction point or a combined approach. A certified installer evaluates the foundation to design a system that actually reaches the target level, as discussed in the guide to a crawl-space radon mitigation system.
How a radon system is tested and verified
A radon system is not finished when the pipe is installed; it is finished when a post-mitigation test confirms it worked. This verification step is what separates a properly completed job from one that merely looks complete.
After installation, the system runs for a period before a follow-up radon measurement is taken, ideally under closed-house conditions in the lowest lived-in level. If the reading sits below the EPA action level, and ideally as low as practical, the system has done its job. If the level remains elevated, the installer troubleshoots, which may mean adding a second suction point, sealing additional air paths, or upsizing the fan.
The manometer on the vent pipe provides ongoing confirmation between formal tests. Its two liquid columns should sit at different heights whenever the fan is running, indicating suction. If they level out, the fan has likely failed and radon protection has stopped, prompting a service call. This combination of a one-time verification test and a permanent visual indicator gives homeowners both proof the system worked and a way to know it keeps working.
Do all homes need a radon system?
Not every home needs mitigation, and the only way to know is testing. Radon levels vary house to house even on the same street, because they depend on the specific soil, foundation condition, and how the home is operated.
The EPA recommends that every home be tested, since radon is invisible and odorless and gives no warning of its presence. A home that tests below the action level does not need a system, though periodic retesting is wise because levels change over time and after renovations. A home testing at or above the action level should be mitigated.
On the Front Range, where elevated radon is widespread, testing is especially worthwhile. Many Colorado homes test high enough to warrant a system, and newer homes are sometimes built with a passive system roughed in, ready to be made active if a test shows it is needed. Treating a radon test as a routine part of homeownership, much like checking smoke detectors, ensures a system is installed only where it actually lowers risk. Local context appears in the guide to a radon home test.
Maintaining a radon system
Radon systems are low-maintenance but not maintenance-free. The fan runs continuously and eventually wears out, typically after many years, at which point it needs replacement to keep the system effective. The manometer is the homeowner’s early-warning tool: if the liquid columns level out, the fan has likely failed.
The EPA recommends retesting every two years, and after any major home renovation or foundation work that could change air-pressure dynamics. Keeping the vent path clear and confirming the fan is running are simple habits that ensure the system keeps protecting the home year after year.
Why radon systems are common on the Front Range
Colorado’s geology gives the Front Range an unusually high share of homes with elevated radon. The granitic and uranium-bearing rock common beneath the region produces radon as it decays, and the gas migrates upward through soil and into homes through foundation cracks, the sump pit, slab penetrations, and gaps around utility lines. Counties including Denver, Boulder, Jefferson, Douglas, and El Paso see a large proportion of tested homes come back at or above the EPA action level, which is why mitigation systems are a familiar sight in basements and on the exterior walls of houses across the region.
Construction patterns reinforce the trend. Many Front Range homes have full basements that are finished into living space, which puts occupants in the lowest level of the home where radon concentrates. Newer Colorado homes are frequently built with a passive system roughed in during construction, a vent pipe routed from beneath the slab to above the roof, ready to be made active with the addition of a fan if a post-construction test shows elevated levels. A homeowner who finds such a stub already in place has a head start, since converting it to an active system is usually simpler and cheaper than installing one from scratch.
How a system interacts with the rest of the home
A radon system does not operate in isolation; it shares the home’s air-pressure environment with the furnace, water heater, fireplace, and exhaust fans. A well-designed system accounts for this, because combustion appliances that draw air for venting can interact with the depressurization the radon fan creates. A reputable installer checks that the system does not cause backdrafting of a furnace or water heater, which would pull combustion gases back into the living space.
Sealing also plays a supporting role. The fan does the primary work, but closing the obvious competing air paths, foundation cracks, the gap around the sump pit, and slab penetrations, lets the system reach lower levels with less effort and a smaller fan. This is why a complete installation pairs the active depressurization with targeted sealing rather than relying on suction alone, and why a post-installation test is the only way to confirm the combined approach actually reached the target.
References
- Consumer’s Guide to Radon Reduction — U.S. Environmental Protection Agency
- Colorado Radon Program — Colorado Department of Public Health and Environment
- Radon and Lung Health — American Lung Association
Front Range homeowners wondering whether their house needs a radon system should start with a test, then talk to a certified installer. Connect with a vetted local professional through our contact page. This guide is informational and not a substitute for professional testing and mitigation advice.