Radon Exhaust System: Parts, Venting and Inspection Checks
A radon exhaust system is the visible half of most radon mitigation jobs: the pipe, fan and discharge point that pull soil gas from under a house and release it outdoors. Buyers usually see it as a white PVC pipe running up a garage wall or the side of the house, often with a small gauge near the bottom. Each part has a job, and each part can be installed or maintained poorly. This guide walks through the components, where EPA says the exhaust should discharge, interior versus exterior routing, Colorado winter issues, noise, an inspection checklist for buyers, and when to retest. It summarizes EPA and CDC guidance current as of 2026; a certified radon mitigation professional should evaluate a specific system, and health questions belong with a physician.
Part of our Radon Mitigation Systems guide — start there for the full picture →
What a Radon Exhaust System Does
Radon is a radioactive gas released from rocks and soil. CDC describes it as odorless and invisible, notes that it can build up inside homes through small cracks and holes, and states that radon is the second leading cause of lung cancer after smoking. EPA’s Citizen’s Guide to Radon recommends fixing a home if the radon level is 4 picocuries per liter (pCi/L) or higher, and adds that levels below 4 pCi/L still pose a risk and in many cases may be reduced. CDC’s prevention page states that EPA also recommends taking action between 2 and 4 pCi/L.
The most common fix is soil suction. EPA’s Consumer’s Guide to Radon Reduction describes active subslab suction, also called subslab depressurization, as the most common and usually the most reliable method. One or more suction pipes go through the floor slab into the crushed rock or soil beneath, and a radon vent fan connected to those pipes draws the gas from below the home and releases it outdoors while creating a negative pressure, or vacuum, under the slab. That negative pressure is what keeps soil gas from leaking up into the living space.
The “exhaust system” is everything from the suction point to the discharge. A related variation draws from a capped sump pit, a drain tile loop, or hollow block walls, and in crawlspace homes EPA describes submembrane suction, where a high-density plastic sheet covers the earth floor and a vent pipe and fan draw radon from under the sheet. EPA calls submembrane suction, when properly applied, the most effective way to reduce radon in crawlspace homes. For a fuller look at the whole system, see the guide to the sub-slab radon mitigation system.
The Parts of a Radon Exhaust System
Suction point
The suction point is where the pipe penetrates the slab, sump lid or membrane. Under the slab, the installer usually excavates a small pit to improve airflow. EPA notes that the number and location of suction pipes depend on how easily air moves in the crushed rock or soil under the slab and on the strength of the radon source, and that often only a single suction point is needed. The penetration should be sealed around the pipe with a durable sealant so the system pulls from below the slab, not from the basement air. A sump used as a suction point needs an airtight cover that still lets the sump drain water; the guide to a radon sump pump cover explains what to look for.
Vent pipe
Most residential systems use rigid PVC pipe, typically 3 or 4 inches in diameter, glued at the joints. Horizontal runs should slope so any condensation drains back toward the suction point rather than pooling in the pipe or fan. The pipe should be supported along its length and protected where it could be struck, such as in a garage near a vehicle.
Inline fan
The fan is the engine. EPA’s Consumer’s Guide states that the exhaust fan must not be located in or below a livable area and should be installed in unconditioned space, and that a fan installed outside must meet local building codes for exterior use. It lists common fan locations as unconditioned home and garage spaces, including attics, and the exterior of the home. The fan should run continuously. EPA writes that the fan should never be turned off and must run continuously for the system to work correctly. Fan models, sizing and life span are covered in the guides to radon fans and radon fan installation.
Discharge point
The discharge is where the gas leaves the pipe, and it is the detail EPA spells out most specifically. In its section on checking a contractor’s work, the Consumer’s Guide states that the exhaust pipes of soil suction systems must vent above the surface of the roof and 10 feet or more above the ground, and must be at least 10 feet away from windows, doors or other openings that could allow radon to reenter the home, if the exhaust pipes do not vent at least 2 feet above these openings. That is EPA’s own wording on location; state rules and industry standards can add requirements, and the installer should be able to explain how the system meets the local rules.
Warning device and manometer
EPA’s Consumer’s Guide states that a warning device must be installed to alert the occupant if an active system stops working properly, and gives examples: a liquid gauge, a sound alarm, a light indicator, and a dial or needle gauge. It adds that the device must be placed where it can be seen or heard easily and that the contractor should check that it works. In its maintenance section, EPA notes that the warning device is usually a manometer and that owners of fan-powered systems should look at it regularly. A U-tube manometer shows the difference in pressure between the pipe and the room; a change from the original reading signals that something has changed. The guide to the manometer gauge explains how to read one.
Labels
EPA states that radon reduction systems must be clearly labeled, so accidental changes do not disrupt how the system works. A typical label identifies the pipe as part of a radon reduction system, gives the installer’s name and contact information, and shows the installation date. Labels on the pipe in the basement, at the fan, and near the electrical disconnect help future owners, inspectors and tradespeople recognize the system.
Electrical
EPA states that electrical connections of all active radon reduction systems must be installed according to local electrical codes. In practice, inspectors look for a proper disconnect near the fan, no extension cords, and outdoor-rated wiring and fittings on exterior fans.
Interior vs. Exterior Routing
Contractors route the vent pipe one of two broad ways, and both appear in EPA’s materials. The Citizen’s Guide notes that a typical system has one pipe penetration through the basement floor and that the pipe may also be installed on the outside of the house.
Interior routing
Here the pipe rises from the basement through a closet, chase or garage, the fan sits in an unconditioned attic or garage space, and the pipe exits through the roof. Interior routing tends to look tidier from the street, keeps the pipe warmer in winter, and puts the discharge above the roof line. It also means more penetrations through floors and the roof, more work to fire-stop and seal those openings, and a fan in the attic that must still sit in unconditioned space under EPA’s guidance.
Exterior routing
Here the pipe exits through a rim joist or foundation wall, the fan mounts on the outside of the house, and the pipe runs up the siding to discharge above the roof edge. Exterior systems are often faster to install and keep the fan outside the living space entirely. They are more visible, the pipe and fan are exposed to weather, and the discharge must still extend above the roof edge rather than ending at the eave or the side of the house.
Neither layout is automatically better. Foundation type, the location of the suction point, roof shape, attic access and appearance all factor in. The guide to radon mitigation systems cost explains how routing affects the price.
Colorado Winters: Condensation, Freezing and Noise
Soil gas drawn from under a slab is usually warmer and more humid than winter air along the Front Range. As it travels through a cold pipe, moisture can condense on the inside walls. In very cold weather, that water can freeze, particularly at the top of an exterior pipe or at the discharge cap, and ice can narrow the opening. Some installers in cold climates favor interior routing, insulated exterior pipe, larger-diameter discharge sections, or fan placements that help condensation drain back down. Practices vary by contractor, and there is no single rule that fits every house.
Signs of winter trouble include a manometer reading that changes during cold snaps, gurgling or dripping sounds in the pipe, ice visible at the top of the stack, and water dripping from fan housings or joints. Owners in high-radon areas of Colorado who see those signs should contact the installer rather than tapping or heating the pipe themselves. Pipe slope matters too: if a horizontal run sags, water can pool, and a pool in front of the fan adds noise and strain.
Noise and vibration
A properly installed fan produces a low hum and a faint airflow sound at the discharge. More noise than that can come from a fan mounted rigidly to framing, a pipe that touches drywall or joists without isolation, water in the pipe, a failing bearing, or a fan that is oversized for the soil conditions. Rubber couplings at the fan, pipe hangers that do not clamp directly against framing, and keeping the fan away from bedrooms all help. A fan that rattles, squeals or grinds is often near the end of its life; EPA notes that fans may last five years or more and that manufacturer warranties tend not to exceed five years. Typical costs are in the guide to radon fan replacement cost.
Radon Exhaust System Inspection Checklist for Buyers
A home inspection may note a radon system, but evaluating its performance is usually a separate service and often outside the standard inspection scope. The checklist below helps buyers and owners know what to look at, and the table summarizes the main components.
| Component | What to check | Warning signs |
|---|---|---|
| Suction point | Pipe penetration sealed to slab, sump lid or membrane | Open gaps around pipe; loose or unsealed sump lid; torn membrane |
| Vent pipe | Glued joints, solid supports, slope back toward suction point | Cracked or separated joints; sagging horizontal runs; dents from vehicles |
| Fan | Running continuously; located in unconditioned space or outside; outdoor-rated if exterior | Silent fan; grinding or rattling; fan inside living space; water leaking from housing |
| Discharge | Above the roof surface, clear of windows, doors and openings per EPA guidance | Pipe ending at the eave or side wall; discharge near a window or deck; ice blocking the cap |
| Warning device | Manometer or alarm visible, readable and showing a reading | Liquid level even on both sides; no gauge at all; alarm disabled |
| Labels | System labeled with installer info and date | No labels; pipe painted over or mistaken for plumbing |
| Electrical | Proper disconnect and wiring per local code | Extension cords; unprotected exterior wiring |
| Test records | Pre- and post-mitigation results available | No post-mitigation test; results older than two years |
Questions to ask the seller
- When was the system installed, and by whom? Is there a warranty?
- What was the radon level before mitigation, and what did the post-mitigation test show?
- Has the fan ever been replaced, and has the manometer reading changed?
- Has the home been remodeled, finished or added onto since installation?
EPA’s Consumer’s Guide notes that sellers of homes with a radon reduction system should inform potential buyers and supply information about the system’s operation and maintenance. A seller who has kept records makes the decision much easier.
How Contractors Design the Exhaust System
The layout of a radon exhaust system is not chosen from a catalog. EPA’s Consumer’s Guide explains that a contractor usually gathers design information from visual inspection, from diagnostic tests or from experience. One diagnostic it describes is chemical smoke: the contractor releases a small amount of smoke into holes, drains, sumps or along cracks and watches where it moves, because the sources of air flow show possible radon routes. Other contractors drill a small test hole some distance from the planned suction point and measure how well suction travels under the slab, which helps decide whether one suction point is enough and how strong a fan is needed.
EPA also notes that a contractor may have concerns about backdrafting of combustion appliances when considering mitigation options and may recommend that the homeowner have those appliances checked by a qualified inspector. That matters most when a fan or suction approach could change pressure in a basement or crawl that contains a furnace or water heater.
Homes with more than one foundation type
Many Front Range houses combine a basement with a crawlspace or a slab-on-grade addition. EPA points out that in these situations a combination of radon reduction techniques may be needed. In practice, that can mean a sub-slab suction point in the basement tied into the same vent stack as a membrane in the crawl, or two separate systems. When a buyer sees a membrane in the crawl with a pipe sealed into it, that pipe is part of the exhaust system too and deserves the same checks as the basement penetration.
What a proposal should spell out
EPA’s checklist for comparing contractor proposals asks whether the estimate includes diagnostic testing before design, installation of a warning device, testing after installation, and a guarantee to reduce radon levels to 4 pCi/L or below, with the length of any guarantee. For the exhaust side specifically, it also helps to see on paper where the pipe will run, where the fan will sit, where the discharge will end relative to windows and the roof line, and how the installer will handle condensation drainage in winter. Clear answers make two bids easier to compare and give a future buyer a record of how the system was meant to work.
A simple owner routine
- Glance at the manometer monthly and note the reading on a piece of tape beside it.
- Listen at the fan a few times a year for new rattles, grinding or silence.
- Look at the top of the stack after a hard freeze for ice at the cap.
- Check that labels are still legible and that no one has boxed in or painted over the pipe.
- Schedule a radon test every two years and after any lower-level remodel.
Testing and Retesting After Mitigation
A good-looking exhaust system is not proof that radon levels are low. EPA’s Consumer’s Guide states that a post-mitigation test should be done within 30 days of installation, but no sooner than 24 hours after the system is operating with the fan on. It notes that the contractor may perform this test but recommends an independent follow-up measurement as well. After that, both EPA guides recommend retesting every two years to confirm levels remain low. EPA also advises retesting in the lowest lived-in area after remodeling, because construction can change how the system performs.
For buyers, a current test during the inspection period is the clearest answer. EPA’s Consumer’s Guide notes that all radon tests should run for a minimum of 48 hours. Results can be compared with the action levels in the radon levels chart, and the guide to radon level in a basement explains why lower-level readings often run higher. Test pricing is covered in the guide to radon testing cost.
When the exhaust system needs attention
Call a qualified mitigation contractor when the manometer reading changes or drops to zero, the fan stops or grows noisy, the pipe cracks or separates, ice repeatedly blocks the discharge, or a retest comes back at or above the action level. EPA advises that if the monitor shows the system is not working properly, the owner should call a contractor to have it checked. EPA’s guide also suggests checking with the state radon office about any state requirements contractors must meet, which is a useful starting point in Colorado. More guides on systems and fans are collected on the radon mitigation hub, and the main radon testing section covers testing basics.
References
- U.S. EPA. Consumer’s Guide to Radon Reduction: How to Fix Your Home (PDF)
- U.S. EPA. A Citizen’s Guide to Radon (PDF)
- CDC. About Radon
- CDC. Preventing Radon Exposure
Frequently asked questions
Where should a radon exhaust pipe discharge?
EPA's Consumer's Guide says soil suction exhaust pipes must vent above the surface of the roof and 10 feet or more above the ground, and at least 10 feet from windows, doors or other openings unless the pipe vents at least 2 feet above them. State and local rules may add requirements.
Can a radon fan be installed inside the house?
EPA states the fan must not be located in or below a livable area and should be in unconditioned space. Attics, garages and the exterior of the home are the common locations EPA lists.
How can a homeowner tell if a radon system is working?
Check the warning device, usually a U-tube manometer, regularly. Uneven liquid levels indicate suction; even levels or a changed reading suggest a problem. A radon test is the only way to confirm the levels themselves.
Do radon vent pipes freeze in Colorado winters?
They can. Moist soil gas condenses in cold pipe, and in very cold weather ice may build at the top of an exterior stack. Pipe slope, routing and pipe insulation help; a changing manometer reading during a cold snap is a reason to call the installer.
How often should a home with a radon system be retested?
EPA recommends a post-mitigation test within 30 days of installation but at least 24 hours after the fan starts, then retesting at least every two years and after remodeling the lower level.
Looking at a house with a radon system and unsure if it checks out? Get in touch with photos of the pipe, fan and gauge and we can point out what to ask the seller and what to test.
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 — $154.03 |
 Radon U-Tube Manometer | Confirms the system is pulling suction. | Amazon — $8.95 |