What Does a Radon Mitigation System Do: 2026 Guide
A radon mitigation system performs one core function: it reverses the natural flow of soil gas so that radon vents safely outdoors above the roofline instead of accumulating inside the home. The system achieves this by creating a slight negative pressure under the foundation, which pulls radon-laden soil gas into a suction pipe rather than allowing it to seep through cracks, joints, and slab penetrations into the living space. Understanding what the system actually does — distinct from what it is — helps homeowners evaluate whether their system is performing, decide between mitigation methods, and recognize when an installation has succeeded. This guide summarizes EPA, CDPHE, and AARST guidance current as of 2026 — consult an NRPP- or NRSB-certified mitigator for installation decisions and your physician for symptoms.
What a radon mitigation system does, in one sentence
The system depressurizes the soil under the foundation so that radon-bearing soil gas is captured and vented outdoors before it can enter the home’s interior air. Everything else — the pipe, the fan, the sealing, the manometer — is in service of that single function. The depressurization typically targets 0.5 to 1.5 inches water column of vacuum across the slab; that small pressure differential is enough to reverse the soil-gas flow direction across all the small cracks and gaps in a typical foundation envelope.
Function 1: capture soil gas before entry
The first action the system performs is capture. The fan creates a vacuum under the slab, which draws soil gas (containing radon and its decay products) into the suction pipe. The capture point is typically a single 4-inch core-drilled hole through the slab, opening to a small plenum carved out of the gravel or soil below. The size of the capture zone — measured by how far across the foundation the depressurization extends — depends on soil permeability, slab integrity, and fan capacity. On a typical basement slab, a single suction point depressurizes the entire foundation footprint of a 1,500 to 3,000 square foot home. Larger or irregular foundations may need multiple suction points.
Function 2: convey the gas to the discharge point
Once captured, the soil gas travels through sealed PVC pipe from the suction point to the discharge point above the roofline. The conveyance function requires absolute pipe integrity — any leak upstream of the fan (i.e., between the suction point and the fan) creates a risk that radon-laden air re-enters the home through the breach. AARST standards require continuous sealed joints, no exposed unions inside conditioned space, and pipe labeling at regular intervals so future occupants and tradespeople can identify the radon system. Conveyance pipes are typically 3-inch or 4-inch PVC, with 4-inch dominating in higher-flow applications.
Function 3: discharge the gas safely
The discharge point releases the radon-bearing soil gas to the outdoor atmosphere where it dilutes harmlessly. AARST standards require the discharge to terminate at least 10 feet above ground level, 10 feet from any operable window or door, and at least 2 feet above any roofline within 10 feet of the discharge. The vertical termination above the roofline ensures the discharged gas does not re-enter the home through windows, eaves, or other openings. The radon levels in the discharged gas are typically much higher than in the indoor air — the entire purpose is concentration of soil gas — so the discharge location matters significantly for safety.
Function 4: maintain continuous depressurization
The fan runs 24/7 to maintain the negative pressure that drives the system. Stopping the fan, even briefly, allows soil-gas pressure to equalize and radon to begin entering the home through foundation gaps. The fan therefore performs the ongoing maintenance function that keeps the system operating; everything else is essentially passive infrastructure. Fan reliability is the single biggest determinant of long-term system performance. Most residential radon fans last 5 to 10 years before requiring replacement; high-quality fans from RadonAway and Festa often exceed 10 years with proper installation and weather protection.
Function 5: provide ongoing performance visibility
The U-tube manometer mounted on the vertical pipe near the fan provides ongoing visibility into system operation. Equal liquid columns indicate the fan has failed or the pipe is blocked; an offset between the columns confirms operating pressure. The manometer is the homeowner’s quickest check on system health. AARST standards require manometer installation on every active soil depressurization system, and the gauge is intended for monthly visual inspection. Newer installations sometimes add an electronic pressure switch with an audible alarm or smart-home notification, but the simple U-tube remains the most common monitoring device.
What the system does NOT do
The system does not remove radon from the indoor air directly — it prevents soil-gas radon from entering. Radon already in the home when the system activates dilutes through normal ventilation over the following weeks; the system reduces ongoing entry but does not actively scrub indoor air. The system also does not affect radon coming from non-soil sources, which are typically minor contributors. Building materials (granite countertops, certain concrete formulations) and well water sources can introduce small amounts of radon independent of soil-gas entry; these are usually below the level requiring intervention and are not addressed by a standard ASD mitigation system. For more on the testing-to-mitigation workflow, see our guide on Colorado radon testing and mitigation.
How the system performance is measured
Two metrics confirm the system is doing its job. Pressure differential — the manometer offset shows the system is maintaining negative pressure under the slab. Indoor radon level — a post-installation test (typically 48 hours with a continuous monitor or a charcoal-canister kit) confirms the indoor concentration is below the target threshold. Mitigators typically target a post-installation indoor level below 2.0 pCi/L (well under the 4.0 pCi/L action level), and many homes achieve 0.5 to 1.5 pCi/L on properly installed systems. The performance ratio (indoor radon before vs after) typically falls in the 50 to 99 percent reduction range depending on starting concentration and home characteristics.
Function under different operating conditions
The system’s performance varies with several environmental factors. Outdoor temperature affects building stack effect; winter cold increases the natural upward air flow through a home and can pull more soil gas into the lower levels. Wind direction and speed affect vent discharge dynamics. Soil moisture changes soil permeability and affects how widely the depressurization extends. HVAC operation creates indoor pressure dynamics that interact with the mitigation system. Most certified mitigators design for the worst-case conditions (winter operation with HVAC running) so the system maintains performance year-round. For broader context on system design, see our guide on radon mitigation techniques.
What active vs passive systems do differently
Active soil depressurization (ASD) uses a fan to create continuous negative pressure — this is the dominant residential design. Passive radon-resistant new construction (PRRNC) uses the same pipe-and-vent infrastructure but no fan; the system relies on stack effect (warm air rising in the vent pipe) to draw soil gas upward and out. Passive systems reduce indoor radon by 30 to 70 percent without electricity but cannot match active-system reduction rates. New construction in many Colorado jurisdictions is required to install passive PRRNC infrastructure under International Residential Code Appendix F; if post-construction testing shows radon above 4.0 pCi/L, the homeowner adds a fan to convert the system from passive to active.
Sealing’s role in what the system does
Sealing visible foundation cracks, sump covers, slab penetrations, and floor-wall joints is a standard component of the system installation. Sealing alone rarely reduces indoor radon below 4.0 pCi/L, but combined with active depressurization it improves the system’s efficiency by reducing the soil-gas flow that must be captured by the suction point. Comprehensive sealing typically reduces fan-power requirements and extends fan life by reducing flow demand. AARST standards require attention to visible soil-gas entry points during system installation, so any reputable mitigator includes sealing as part of the package.
When the system is doing its job correctly
Three indicators confirm correct operation. The manometer shows the expected pressure differential (typically 0.5 to 1.5 inches water column offset between liquid columns). The post-installation indoor radon test shows levels below the target threshold (usually 2.0 pCi/L or lower). Annual follow-up indoor radon tests continue to show levels in the same range. If all three hold, the system is performing its function as designed. If any one degrades — manometer equalizes, indoor radon rises above target, follow-up tests trend upward — the system needs maintenance attention.
How the system handles seasonal variation
Indoor radon levels typically vary by season, with winter levels 20 to 50 percent higher than summer levels in most Colorado homes. The variation is driven by stack effect — warm interior air rises and exits through the upper levels of a tightly built home, creating a slight negative pressure on the lower levels that draws additional soil gas inward. A properly designed mitigation system handles this seasonal variation by maintaining sufficient depressurization across all operating conditions. Mitigators size fans for worst-case winter operation; summer performance is typically 10 to 20 percent better than the winter baseline. Homeowners who add a continuous radon monitor can observe the seasonal pattern directly and confirm the system is keeping the elevated winter levels under control.
What happens with crawlspace foundations
Crawlspaces present a different mitigation problem than basements or slab-on-grade homes. The soil under a crawlspace is typically exposed (no slab) and can produce significant soil-gas flow into the conditioned space above. The standard solution is sub-membrane depressurization (SMD): a sealed polyethylene sheet is installed over the entire soil surface, with the suction pipe drawing from beneath the membrane. The membrane creates the pressure-differential surface that the slab provides in basement installations. SMD systems require careful installation to seal the membrane edges against the foundation walls; gaps or tears reduce performance significantly. Crawlspace mitigation typically costs more than basement mitigation ($2,000 to $4,000) due to the additional sealing labor.
What the system does for combustion safety
A radon mitigation system depressurizes the soil under the foundation, but in a tight home it can also slightly depressurize the indoor air relative to outdoor. If the home has atmospherically vented combustion appliances (older gas furnaces, gas water heaters, fireplaces with open dampers), the indoor depressurization can occasionally cause backdrafting — combustion exhaust drawn back into the home rather than rising up the flue. AARST standards require mitigators to check combustion-appliance operation after installation and either confirm safe operation or recommend appliance upgrades. Newer sealed-combustion or direct-vent appliances are immune to backdrafting concerns. Homeowners with older atmospherically vented equipment should mention this to the mitigator before installation so the post-install verification covers combustion safety.
References
- EPA Radon Program Overview — U.S. Environmental Protection Agency
- CDPHE Colorado Radon Program — Colorado Department of Public Health and Environment
- CDC Radon Health Resources — Centers for Disease Control and Prevention
- American Lung Association Radon Resources — American Lung Association
Front Range homeowners considering radon mitigation can reach our team through the contact page for a referral to a certified installer.
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 |