Radon Vent: What Homeowners Need to Know
The radon vent is the pipe that does the actual work of getting radon out of a home — yet it is the part homeowners understand least. It is more than a length of PVC; where it starts, how it is routed, and exactly where it discharges all determine whether a mitigation system reduces radon or merely moves the problem around. On the Colorado Front Range, where indoor radon runs high across the region, getting the vent right matters. This guide summarizes EPA and Colorado Department of Public Health and Environment guidance current as of 2026 — consult a certified radon professional for system design, since vent routing depends on your home’s foundation and layout.
What is a radon vent and what does it do?
A radon vent is the pipe in a radon mitigation system that carries radon-laden soil gas from beneath the foundation up and out of the home, discharging it above the roofline where it disperses safely. In an active system, a fan pulls the gas through this pipe; in a passive system, natural air movement and the stack effect draw it upward. The vent is what separates a working mitigation system from a sealed-up basement — it gives the radon a controlled exit path rather than letting it accumulate indoors. The pipe is typically 3- or 4-inch PVC sealed into the slab at the suction point.
The vent is one component of a larger system; how it connects to the suction point and fan is covered in the guide to radon testing in Colorado and the mitigation resources within it.
How the vent pipe is routed
Routing the vent is a design decision, not an afterthought. There are two common paths:
- Interior routing: the pipe runs up through the house — often through a closet, garage, or chase — into the attic, where the fan sits, then through the roof. This keeps the pipe and fan inside conditioned or semi-conditioned space and is cleaner in appearance.
- Exterior routing: the pipe exits low on the foundation and runs up the outside wall to a fan mounted outdoors, terminating above the eave. This is simpler to install but more visible and exposes the fan to weather.
Either path can work well when executed correctly. The pipe should slope back toward the suction point so condensation drains down rather than pooling, and it should avoid sharp bends that reduce airflow. The way the vent integrates with the rest of the assembly is detailed in the guide to radon mitigation installation.
Condensation management is easy to overlook but important. As warm, moist soil gas rises through the cold upper section of pipe — especially through an unheated attic in a Colorado winter — water vapor condenses on the inside walls. If the pipe is pitched correctly back toward the suction pit, that water drains harmlessly into the soil. If a low spot or a sag traps it, the pooled water restricts airflow, can freeze, and reduces the system’s effectiveness. A continuous slope and properly supported pipe prevent the problem.
Discharge placement rules
Where the vent terminates is governed by EPA guidance, and it is the detail most often gotten wrong. The discharge point should be:
- Above the roof eave — typically at or above the highest roofline so the gas disperses high and away from the living space.
- Away from windows, doors, and air intakes — generally at least 10 feet from any opening into the home or a neighbor’s, so exhausted radon does not re-enter.
- Clear of decks and occupied areas where people might breathe the discharge.
A vent that ends below a window or too close to an HVAC intake can recirculate radon back inside, defeating the system. This is one reason a discharge terminated at ground level or under an overhang is a red flag worth correcting. The fan that drives the discharge is covered in the guide to the radon mitigation fan.
Passive versus active vents
Some homes — especially newer Colorado builds constructed with radon-resistant features — have a passive vent installed during construction: a sealed pipe from the sub-slab to the roof with no fan, relying on the natural stack effect to draw radon upward. Passive systems reduce radon modestly but often not enough on their own in a high-radon area.
The advantage is that a passive vent is easy to convert: a contractor simply adds an inline fan to the existing pipe, turning it into an active system that performs far better. If a home has a passive vent and a test still shows elevated radon, activating it with a fan is usually the quickest, cheapest fix. The cost picture for adding the active component appears in the guide to the cost of radon mitigation.
Many newer Colorado homes were built with passive radon-resistant features under modern building practices: a gravel layer beneath the slab, a vapor barrier, a sealed sump, and a capped vent pipe stubbed up through the roof. A homeowner who sees a capped white pipe in the attic of a recently built house likely has a passive system waiting to be activated. Testing tells whether activation is needed, and if so, the upgrade is among the least expensive radon fixes available because the pipe routing is already in place.
Common vent mistakes
Several recurring errors undermine an otherwise sound system:
- Discharge too low or near a window — recirculates radon back indoors.
- Undersized or sagging pipe — restricts airflow and traps condensation.
- Fan mounted in living space — any pipe leak on the pressure side would push radon into occupied air, which is why the fan belongs in an attic, garage, or outdoors.
- No manometer — leaves the homeowner with no way to see whether the fan is moving air.
- Unsealed suction point — reduces the suction the vent can apply under the slab.
A post-installation radon test catches the consequences of these mistakes; the manometer catches the day-to-day function. Both should be present on a properly finished system.
Vent materials, sizing, and code considerations
The vent pipe is almost always rigid PVC, typically 3 or 4 inches in diameter, chosen for durability and smooth interior walls that do not restrict airflow. Larger 4-inch pipe is common because it moves the required air with less resistance, letting the fan work efficiently. Flexible or corrugated pipe is avoided in the main runs because its ridged interior creates turbulence that reduces airflow and can trap condensation.
Sizing the vent to the fan and the sub-slab conditions is part of good design. An undersized pipe paired with a strong fan creates excess noise and resistance; an oversized pipe with a weak fan may not maintain enough velocity to carry condensation back to the suction point. Matching the components is why a thoughtful contractor specifies both together rather than grabbing whatever is on the truck.
Local building codes and radon standards influence the installation. Many jurisdictions reference recognized radon mitigation standards that govern discharge height, clearance from openings, fan placement outside living space, and labeling of the system. Newer Colorado construction often includes rough-in provisions for radon under modern building practices, which is why a recently built home may already have a capped vent ready for a fan. A homeowner does not need to memorize the code, but should confirm their contractor follows recognized standards — that adherence is what separates a system that merely looks right from one that performs and will pass scrutiny at resale.
When to have the vent checked or corrected
Have a certified radon professional evaluate the vent if a test shows elevated radon despite a system being present, if the discharge terminates near a window or below the roofline, if the fan is mounted inside the living space, or if there is no manometer. Correcting a vent’s routing or discharge is far cheaper than living with a system that does not work. After any change, re-test to confirm the home is below the EPA’s 4.0 pCi/L action level. For questions about health effects of past radon exposure, consult a physician — the vent’s job is to manage the gas going forward.
The manometer: reading the vent’s performance
Every active radon vent should have a manometer — a small U-shaped tube partly filled with colored liquid, mounted on the pipe near the fan or at eye level. It is the simplest, most reliable way for a homeowner to confirm the system is working day to day. When the fan is running and drawing air through the vent, the liquid sits at different heights on the two sides of the U, showing the pressure difference the fan creates. When both sides are level, the fan is off or has failed.
Homeowners should glance at the manometer periodically and note the normal reading shortly after installation, so a future change is easy to spot. A sudden shift to a level reading means the fan has stopped — time to call a contractor for a replacement. A gradual change can indicate a developing blockage, a condensation problem, or a leak in the vent. The manometer does not measure radon directly; it measures whether the vent is moving air, which is the precondition for the system reducing radon.
The manometer pairs well with periodic radon re-testing. The gauge confirms the vent is functioning mechanically; a re-test every couple of years confirms the result — that the home is actually staying below the action level. Together they cover both halves of the question: is the system running, and is it working? A vent with a healthy manometer reading and a low re-test result is doing exactly what it was installed to do, which is the outcome every Front Range homeowner with a radon system is looking for.
For all its modest appearance, the vent is the component that actually carries radon out of the home, and the details of its routing and discharge are what separate a system that protects a household from one that merely looks the part. A homeowner does not need to become an expert in pipe sizing or stack effect, but knowing what a correctly installed vent looks like — discharging above the roofline, well away from windows, with the fan outside living space and a manometer in view — lets them recognize good work and question bad work. On the high-radon Front Range, where a great many homes need mitigation, that ability to tell the difference is worth having, whether evaluating a system during a purchase or confirming one in a home already owned.
If anything about an existing vent looks off — a discharge near a window, a fan in the basement, a missing manometer, or a system that still pairs with a high radon reading — the right move is to bring in a certified radon professional rather than living with a system that may not be doing its job. Vent corrections are usually far cheaper than a full new installation, since the suction point and much of the routing are already in place. The reassuring takeaway is that a flawed vent is almost always fixable, and a correctly functioning one quietly protects the home for years with nothing more than an occasional glance at the gauge and a periodic re-test.
References
- Consumer’s guide to radon reduction — U.S. Environmental Protection Agency
- Radon mitigation guidance for Colorado — Colorado Department of Public Health and Environment
- Radon and lung health — American Lung Association
If your Front Range home has a radon vent you are unsure about, connect with us here to have a certified radon professional evaluate the system.
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 |