Radon Gas Mitigation System: What Homeowners Need to Know
A radon gas mitigation system is a permanent installation that lowers the indoor radon concentration in a home, typically by drawing radon-laden air from beneath the foundation slab and venting it above the roofline. The most common design is called active sub-slab depressurization (ASD), and it is the recognized standard recommended by the EPA for nearly all U.S. homes with elevated radon. This guide summarizes EPA, CDPHE, and trade-association guidance current as of 2026 — it is informational, not medical advice. Hire a Colorado-certified radon mitigation professional for design and installation in your specific home, and consult a physician for any health concerns related to long-term exposure. The aim here is to give homeowners a clear picture of how mitigation works, what it costs, and what to expect during and after installation.
What is a radon gas mitigation system?
A radon gas mitigation system is a permanent collection of components designed to reduce indoor radon concentrations to as far below the EPA action level (4.0 pCi/L) as practical. The most common type — active sub-slab depressurization — uses a fan to create a slight negative pressure under the home’s foundation slab, drawing soil gas (which contains radon) out before it can enter the living space. The collected gas is vented through a sealed pipe up and out above the roof.
Other system types exist for specific situations. Sub-membrane depressurization is used for homes with crawlspaces; the membrane is sealed over the soil and the fan pulls gas from beneath it. Block-wall depressurization addresses homes with hollow concrete-block foundations where radon enters through the wall cores. Drain-tile depressurization uses an existing perimeter drain system as the suction point. Each variant follows the same principle: collect soil gas before it enters the home and vent it safely outside.
Most Colorado Front Range homes with elevated radon receive a standard active sub-slab depressurization system, often with a single suction point installed through the basement slab or garage floor. The parent guide to radon testing for Front Range homeowners covers when testing leads to mitigation and how to plan for it.
How active sub-slab depressurization works
The system has four main components: a suction point cut into the foundation slab, a sealed vertical pipe (typically 3-inch or 4-inch PVC) running from the suction point to above the roofline, an inline fan installed outside the conditioned space (typically in the attic or on the exterior wall), and a U-tube manometer or pressure gauge that confirms the system is operating.
The fan pulls air from beneath the slab at a low flow rate but a continuous duty cycle. The negative pressure under the slab is small — typically less than 1 inch of water column — but enough to reverse the gradient that would otherwise push radon up through cracks, joints, and penetrations. The collected gas exits above the roof, where it disperses into the atmosphere at concentrations far below outdoor health concerns.
System design depends on home characteristics. Slab construction (poured concrete, with or without an aggregate base), foundation type (slab-on-grade, basement, crawlspace, mixed), home size, soil conditions, and existing penetrations all influence where the suction point goes and how the pipe is routed. A certified mitigation professional performs a diagnostic test before designing the system, often using smoke pencils and pressure measurements to map sub-slab communication.
What a radon gas mitigation system costs
Typical residential installation costs in 2026 run $1,200 to $2,500 for a standard system in a slab-on-grade or basement home with straightforward access. Pricing depends on:
- Number of suction points (most homes need one; large or complex foundations may need two or three)
- Pipe routing complexity (attic-routed systems are typically less expensive than exterior wall-routed)
- Aesthetics (interior pipe runs cost more but look cleaner; exterior runs are cheaper but visible)
- Foundation type (crawlspaces with sub-membrane work cost more)
- Geographic factors (Front Range labor and material rates)
Mountain markets, rural properties, and homes with multiple foundation types or unusual configurations can cross $3,500. Crawlspace mitigation with full sub-membrane installation typically runs $2,500 to $5,000. The cluster article on radon mitigation cost in 2026 covers detailed pricing scenarios across the Front Range.
Operating cost is modest. The fan typically draws 50 to 100 watts continuously, which translates to roughly $5 to $15 per month in electricity at typical Colorado utility rates. Fans last 5 to 10 years on average and cost $150 to $400 to replace, plus labor.
What to expect during installation
Installation typically takes one full day for a standard system, sometimes two days for complex configurations or when significant pipe routing is required. The mitigation contractor cuts a small hole (typically 5 to 6 inches) through the slab at the chosen suction point, removes a small amount of aggregate beneath, installs the suction pit and pipe, and seals the slab penetration.
The pipe runs up through the home or along the exterior to above the roofline. Interior routes typically go through a closet or chase to the attic and then through the roof. Exterior routes mount to the side of the home and extend above the roof or eave. The fan installs inline somewhere outside the conditioned space (typically in the attic for interior runs, or in the upper part of the exterior pipe for exterior runs).
The contractor seals visible foundation cracks and penetrations to improve system performance. Sump pump pits, if present, are typically sealed with a gasketed lid that allows access for service. Floor drains may need traps to prevent depressurization from drawing sewer gas. Once the system is operating, the contractor verifies pressure at the manometer and explains how to read it for ongoing operation checks.
Verifying the system works: post-installation testing
Mitigation systems should be tested after installation to confirm they reduce indoor radon below the EPA action level. The standard procedure is a 48-hour continuous monitor test or a 2-day charcoal canister test, performed 24 to 48 hours after the system is energized. Many mitigation contractors include the post-installation test in the installation price; others charge $125 to $200 separately.
EPA guidance recommends retesting every two years thereafter to confirm continued performance. Mitigation systems can degrade over time as fans wear, seals fail, or building modifications change the pressure dynamics. A consumer-grade continuous radon monitor (around $200 to $300) provides ongoing visibility without lab-tested formal results.
Most mitigation contractors warranty their work for one to two years on workmanship and offer service plans for ongoing maintenance. Fans typically last 5 to 10 years; replacement is straightforward and costs $150 to $400. Manometer fluid evaporates over time and may need topping up. The cluster article on DIY radon test accuracy covers post-mitigation monitoring options for homeowners.
Common installation choices and trade-offs
Homeowners installing a radon gas mitigation system make several design choices that affect both cost and aesthetics. Interior versus exterior pipe routing is the biggest. Interior routes (through a closet, chase, or storage area to the attic) cost more but keep the system invisible from the exterior. Exterior routes (mounted on the outside of the home) cost less but show a 3-inch or 4-inch white PVC pipe running up the side of the house.
Suction point location is another choice. Basement installations typically place the suction in an unfinished mechanical room or storage area, where the slab penetration is hidden. Garage installations work well for slab-on-grade homes; the pipe rises through the garage attic and out the roof. Some homeowners choose the more discrete location even at slightly higher cost.
Fan location and noise also matter. Inline fans installed in unconditioned attic space are usually inaudible from living spaces. Fans in exterior pipe runs produce a slight hum audible if the pipe runs near a bedroom window. Higher-quality fans run quieter; budget fans can be loud enough to notice in nearby rooms. Discuss fan placement with the contractor before installation, particularly if the home has bedrooms close to the planned exterior pipe location.
References
- EPA Consumer’s Guide to Radon Reduction — U.S. Environmental Protection Agency
- CDC radon health information — Centers for Disease Control and Prevention
- CDPHE Colorado radon program and certified contractor list — Colorado Department of Public Health and Environment
- EPA radon professional certification information — U.S. Environmental Protection Agency
Front Range homeowners considering radon mitigation or system upgrades can connect with a vetted local inspector through our contact page for a referral to a certified Colorado radon mitigation 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 — $148.29 |
 Radon U-Tube Manometer | Confirms the system is pulling suction. | Amazon — $10.99 |