Radon Mitigation System Diagram: Parts Explained
A radon mitigation system looks simple from the curb, a white pipe running up the side of a house, but the diagram of how it works reveals careful engineering beneath the slab. Understanding a radon mitigation system diagram helps homeowners verify their system is installed correctly, read an inspector’s report, and know what each part does. This guide summarizes EPA and Colorado guidance current as of 2026 and is informational only; consult a certified radon professional for installation or evaluation decisions. Below: a component-by-component walk through the standard diagram, how gas is routed out, and what the labels mean.
What Does a Radon Mitigation System Diagram Show?
A typical diagram shows an active sub-slab depressurization system, the most common design. Reading it from the bottom up, the diagram depicts a suction point cut into the concrete slab, a pit excavated in the soil or gravel beneath, a vent pipe rising from that point, an inline fan that creates suction, and an exhaust point above the roofline where radon-laden gas is released safely into the outdoor air. A manometer (pressure gauge) on the pipe confirms the fan is pulling.
The diagram illustrates the central principle: rather than trying to block radon, the system collects soil gas before it enters the home and routes it outside. By depressurizing the space under the slab, the fan reverses the natural pressure that would otherwise draw radon up through cracks and penetrations. This is why the design is called “active soil depressurization,” a concept the broader Colorado radon testing guide explains in the context of why Front Range homes are prone to elevated radon.
The Suction Point and Sub-Slab Pit
At the base of the diagram is the suction point, the heart of the system. A hole is cored through the concrete slab, usually in the basement floor, and a pit is excavated in the soil or aggregate beneath. This pit creates a void where the fan’s suction can spread across a wide area under the slab, drawing soil gas toward the pipe rather than letting it seep up into the living space.
The effectiveness of this single point depends on what lies beneath the slab. A bed of clean gravel allows suction to communicate widely; compacted soil or fill restricts it, sometimes requiring multiple suction points. Mitigators perform diagnostic “communication” testing to decide how many points a home needs. The diagram may show one point for a small, gravel-bedded slab or several connected points for a larger or poorly communicating one. This sub-slab work is the foundation of the active radon mitigation system, and getting it right matters more than any visible component.
The Vent Pipe and Routing
From the suction point, the diagram traces a vent pipe, typically PVC, upward and outward to the exhaust above the roof. Routing follows two rules visible in any good diagram: the pipe must run from the suction point to a discharge point above the roofline, and it should rise continuously so any condensation drains back down to the soil rather than pooling in the pipe.
There are two common routing styles the diagram may show. An interior routing runs the pipe up through the house and out the roof, which hides the pipe and discharges high above windows. An exterior routing exits the rim joist near the floor and runs up the outside wall to above the eave. Both must terminate at a height and distance from windows, doors, and other openings that prevent the exhausted radon from re-entering the home. The visible exterior pipe many homeowners recognize is detailed in the guide to the radon pipe and its placement rules.
The Fan and Where It Sits
The inline radon fan is the powered component, and the diagram always shows it located outside the living space, in the attic, in the garage, or outdoors on the exterior pipe, never in a basement or other occupied area. This placement matters: keeping the fan downstream of the conditioned space ensures that any leak in the pressurized portion of the pipe vents radon outdoors rather than back into the home.
The fan runs continuously, drawing soil gas up through the suction point and pushing it out the exhaust. Fans are sized to the suction demand the diagnostics revealed, more restrictive sub-slab conditions need a stronger fan. The diagram may label the fan’s position relative to the manometer so a reader can confirm the gauge sits on the suction side. Homeowners curious about how the powered design compares to passive setups can read how the radon mitigation system works end to end.
The Manometer and System Labels
A small U-shaped or digital manometer appears on the diagram mounted on the vent pipe inside the home, usually in the basement. This pressure gauge is the homeowner’s at-a-glance health check: when the fan is running and pulling properly, the liquid columns sit at different heights, or the digital display shows a pressure reading. If the two columns level out or the reading drops to zero, the fan has likely failed and the system needs service.
The diagram also typically shows a system label, a tag required in many jurisdictions and recommended by standards, listing the installer, install date, and instructions. Some systems include a fan failure warning device, a light or alarm, that supplements the manometer. Reading these indicators is part of routine radon mitigation system maintenance, and a quick monthly glance at the manometer catches most problems before radon levels climb.
How to Use the Diagram to Evaluate Your System
Walk your own system against the diagram. Confirm the fan sits outside occupied space, the pipe rises continuously and discharges above the roofline away from windows, the manometer shows a pressure difference, and a system label is present. If your home has a sump pit, the diagram for a sump-integrated system will show the suction drawn from a sealed sump lid, a common Front Range configuration.
If any element is missing, an unlabeled fan in a basement, a manometer reading zero, an exhaust discharging beside a window, that is a flag to call a certified radon professional. After any installation, the only true confirmation the diagram cannot provide is a follow-up radon test showing levels below the EPA action level of 4.0 pCi/L. A diagram explains how the system should work; a post-mitigation test proves it actually does. Pairing the visual understanding with verification testing is how homeowners confirm their investment is protecting them.
Variations the Diagram May Show
Not every system looks identical, and the diagram for your home reflects its specific construction. The most common variation is the routing path. An interior diagram runs the pipe from a basement suction point up through closets or chases and out the roof, keeping the pipe hidden and discharging well above the home. An exterior diagram shows the pipe exiting near the floor through the rim joist, then running up the outside wall to terminate above the eave. Both are valid; the choice depends on the home’s layout, aesthetics, and the easiest path to a compliant discharge point.
Foundation type changes the bottom of the diagram. A home over a crawl space uses sub-membrane depressurization, the diagram shows a plastic membrane laid over the soil, sealed at the edges, with the suction drawn from beneath it rather than from a slab pit. A home with a sump pit may show a sealed sump lid serving as the suction point, a common Front Range configuration where the sump connects to the sub-slab drain tile. Multiple suction points appear on diagrams for larger homes or those with poor sub-slab communication, with the pipes joining into a single riser and fan. These configurations all apply the same depressurization logic shown in the basic active radon mitigation system, just adapted to the foundation.
Some diagrams also include a fan-failure alarm or warning light wired to alert occupants if suction is lost, supplementing the manometer. Recognizing which variation matches your home helps you read your own system accurately and spot if a component has been omitted or installed incorrectly.
The Physics the Diagram Represents
Behind the simple lines of a radon diagram is a clear physical principle worth understanding. Radon enters a home because of a pressure difference: the air inside a heated home is slightly lower in pressure than the soil gas beneath the foundation, so the higher-pressure soil gas, carrying radon, is drawn up through cracks, slab penetrations, and gaps. This is sometimes called the stack effect, and it is why radon levels are often highest in the lowest level of a home and during colder months when the heating-driven pressure difference is strongest.
An active mitigation system, the one the diagram depicts, defeats this by reversing the pressure relationship right at the slab. The fan pulls air from beneath the slab, lowering the pressure there below the pressure inside the home. With the pressure gradient reversed, soil gas no longer flows up into the living space; instead it flows into the suction pit, up the pipe, and out the exhaust. The diagram’s arrows, if present, trace exactly this path. Understanding the physics makes the diagram intuitive: every component exists to establish and maintain that reversed pressure field, which is why the same logic underlies the explanation of how a radon mitigation system works.
This also explains why sealing matters. The diagram may show caulking at major cracks and a sealed sump lid not because sealing alone stops radon, it does not, but because unsealed openings let the fan waste suction pulling conditioned indoor air instead of soil gas. Good sealing lets the fan apply its pressure where it counts, beneath the slab, making the whole system more efficient. Reading the sealing details on a diagram tells you whether the installer understood this principle.
Using the Diagram for Maintenance and Resale
A clear system diagram is a practical document beyond installation day. For maintenance, it tells you and any service technician where each component sits, helpful when a fan needs replacing or a manometer reads abnormally. Keeping the diagram with your home records, alongside the post-mitigation test results and the system label information, gives a future technician an instant map of what they are working on.
At resale, the diagram and test records reassure buyers and their inspectors that a working, properly designed system is in place. A buyer’s home inspector can compare the installed system to the diagram to confirm it meets best practice, and the documented radon results show the system achieved acceptable levels. In radon-prone areas like Colorado’s Front Range, a documented, well-designed mitigation system is a selling point rather than a red flag. Pairing the diagram with periodic retesting, the upkeep covered in the guide to radon mitigation system maintenance, keeps both the protection and the documentation current for as long as you own the home.
Common Diagram Mistakes and Red Flags
Reading a diagram against your installed system can expose problems an untrained eye would miss. The most serious red flag is a fan located inside conditioned living space, in a basement utility room, for example. The pressurized portion of the pipe downstream of the fan must run through unconditioned space so that any leak vents radon outdoors, not back into the home. A diagram showing, or a system with, a basement-mounted fan violates this principle and should be corrected.
Discharge placement is another frequent issue. The exhaust must terminate above the roofline and a sufficient distance from windows, doors, and other openings, including a neighbor’s, so the released radon disperses rather than re-entering. A pipe that discharges low on a wall, beside a window, or under a deck defeats the purpose. The diagram should clearly show the discharge clearing the roof and standing apart from openings. A manometer reading zero, an unlabeled system with no installer information, or a pipe that dips and traps condensation are further signs that the installation departs from the diagram’s intent.
When your system diverges from a correct diagram, the fix is a call to a certified radon professional rather than a do-it-yourself adjustment, since fan relocation, rerouting, and discharge changes affect both safety and performance. The point of learning to read the diagram is not to become your own installer but to become an informed owner who can recognize when something is wrong and verify, after any correction, that a follow-up radon test confirms the system actually delivers safe levels.
References
- A Consumer’s Guide to Radon Reduction — U.S. Environmental Protection Agency
- Radon Mitigation Guidance for Colorado Homeowners — Colorado Department of Public Health and Environment
- Radon and How to Reduce It — American Lung Association
Front Range homeowners who want their system evaluated against a proper diagram can reach out through our contact page to connect with a certified local radon professional.
Radon mitigation fans & parts
If a sub-slab depressurization system is the fix, the inline fan is the heart of it. Match the fan to your soil and pipe diameter — or have a certified installer size it.
| Product | Why | Buy |
|---|---|---|
 RadonAway RP145 Inline Fan | Common 4-in. SSD workhorse fan. | Amazon — $152.00 |
 Fantech Rn2 Radon Fan | Quiet operation; energy-efficient. | Amazon — $165.24 |
 Radon U-Tube Manometer | Confirms the system is pulling suction. | Amazon — $13.95 |