Radon Gas Removal System: How It Actually Works
A radon gas removal system is the residential or commercial installation that prevents indoor radon accumulation. The phrase removal is slightly misleading. The system does not destroy radon gas; radon decays naturally on a 3.8-day half-life regardless of any intervention. What the system actually does is redirect soil-gas flow, drawing the radon-laden air from beneath the building foundation and venting it to the exterior before it can enter habitable rooms. This guide explains the gas-removal mechanism, the fan-curve specifications that determine system effectiveness, and the manometer-based pressure monitoring that confirms the system is operating. The information summarizes EPA and CDPHE guidance current to 2026; specific system design and installation should be assigned to a CDPHE-certified mitigation professional.
What a radon gas removal system actually does
The system creates a controlled negative-pressure zone beneath the building foundation. Soil gas that would otherwise be drawn upward through cracks, slab penetrations, sump pits, and crawlspaces due to indoor-outdoor pressure differentials is instead pulled laterally toward the system’s suction point and discharged through a vent pipe to the exterior atmosphere. Once outside, the radon disperses into ambient air and decays naturally without ever entering occupied spaces. The parent radon testing in Colorado pillar covers the testing protocols that identify when the system is needed.
The mechanism is gas-flow redirection, not gas destruction. This distinction matters because some marketing materials describe radon mitigation as removal in a way that implies the radon is eliminated. The radon is not eliminated; it is simply prevented from entering the home. The reduction in indoor concentration is real (80 to 95 percent typical), but it is achieved by changing where the gas ends up, not by neutralizing it. A look at radon system engineering covers the broader mitigation system landscape.
The sub-slab depressurization standard
Sub-slab depressurization (SSD) is the dominant residential radon gas removal system in 2026. The system has four functional zones.
The suction footprint
Beneath the foundation slab, an air gap exists in the gravel or soil layer where the slab meets earth. The suction point is a single core-drilled opening through the slab that connects to this air gap. The fan’s negative pressure propagates outward through the permeable layer, creating a depressurization footprint that extends 15 to 40 feet from the suction point depending on soil conditions.
The collection pipe
3-inch or 4-inch schedule 40 PVC pipe runs from the suction point upward through the home to an exterior discharge above the roof line. The pipe is sized to maintain low resistance to airflow while keeping installation cost reasonable.
The fan
An electric in-line fan installed in the piping (typically in the attic, garage, or exterior wall) creates the negative pressure that drives soil-gas flow. Common Front Range residential fan selections include the RadonAway RP145 (entry-level, 60-80 CFM, 0.5 to 1.0 in. WC vacuum), RP265 (mid-range, 100-150 CFM, 0.8 to 1.5 in. WC), and HP series (high-performance, 150-250 CFM, 1.0 to 2.5 in. WC). Fan selection depends on the foundation size, soil permeability, and target negative pressure.
The vent termination
The discharge pipe terminates above the roof line, at least 10 feet above grade and away from operable windows or doors. The radon exits the system at this point and disperses into ambient outdoor air.
Fan-curve specifications
The fan is the engine of the gas removal system, and its performance characteristics determine whether the system actually achieves its design target. Each radon fan model is characterized by a fan curve plotting airflow (CFM) against static pressure (in. WC of vacuum). Higher static pressure correlates with higher gas removal effectiveness for tight or low-permeability foundations; higher airflow correlates with broader depressurization footprint for permeable foundations.
A working CDPHE-certified installer selects the fan based on the home’s actual conditions. A home with a clean gravel sub-slab layer and a 1,200 square foot footprint typically needs an RP145 generating roughly 80 CFM at 0.7 in. WC. A home with poorly compacted soil and a 2,400 square foot footprint may need an HP series fan generating 180 CFM at 1.4 in. WC to achieve the same depressurization across the larger area.
Undersized fans are one of the most common mitigation-failure modes on the Front Range. Contractors quoting tight bids occasionally specify a smaller fan than the application warrants, then face callback work when the post-installation radon test still reads above 4.0 pCi/L. Homeowners should ask which fan model is being specified and how the selection matches the home’s foundation and soil characteristics. A look at radon entry causes covers why some homes need stronger fan specs.
Manometer pressure monitoring
The U-tube manometer is the small visible gauge mounted on the indoor portion of the vent pipe. It measures the negative pressure inside the pipe (in inches of water column) and displays the reading visibly so the homeowner can verify at a glance that the system is operating.
A properly operating residential SSD system typically shows 0.5 to 1.5 in. WC negative pressure on the manometer. A reading of zero or near-zero indicates either a fan failure, a power outage, or a major leak in the system piping. A reading dramatically higher than the design target (3.0 in. WC or more) indicates a possible airflow restriction (blocked pipe, clogged suction pit) and warrants investigation.
Homeowners should check the manometer monthly as part of routine home maintenance. The check takes 5 seconds and catches fan failures before they go undetected for weeks. A failed fan that goes undetected returns the home to pre-mitigation radon conditions until the fan is repaired or replaced. A look at radon testing inspection covers post-mitigation verification including manometer monitoring.
How the gas-flow physics work
The system relies on three physics principles working together.
Pressure differential
Soil gas naturally flows from areas of higher pressure to areas of lower pressure. The fan creates a region of reduced pressure beneath the foundation, which becomes the lowest-pressure point in the relevant flow network. Soil gas that would otherwise rise into the home is instead drawn toward this low-pressure zone and into the vent pipe.
Continuous operation
The fan must run continuously, not on demand, because radon entry into the home is continuous. Cycling the fan on and off (some homeowners try to save electricity by turning it off at night) defeats the gas-removal mechanism because radon accumulates rapidly during off periods. Annual electricity cost for continuous operation is typically $50 to $130 at Colorado utility rates.
Buoyancy and stack effect
Warm air rises. Inside a heated home in winter, warm indoor air rising through the upper floors creates a slight negative pressure at the foundation level, which drives the stack effect that pulls soil gas into the basement. The mitigation system’s negative pressure must be stronger than the stack effect’s negative pressure for the system to redirect the gas flow effectively.
Variations and alternatives
Sub-membrane depressurization
For crawlspace foundations, the system uses a vapor barrier (typically 6-mil polyethylene) sealed across the crawlspace floor, with the suction point and vent pipe drawing from beneath the membrane. The physics is similar to slab depressurization but the membrane creates the depressurization zone instead of the slab.
Drain tile depressurization
For homes with interior perimeter drain tile, the suction point can connect to the drain tile itself, using the existing pipe network as the depressurization footprint. This approach is less common than slab depressurization but works well in homes designed with interior perimeter drainage.
Block wall depressurization
For homes with hollow concrete block foundation walls, the suction point can draw from the hollow block cavities, which connect through the wall and provide a depressurization path along the wall plane. Used in older homes where the block-wall design supports it.
System longevity and maintenance
A properly installed radon gas removal system requires minimal maintenance. The PVC piping, manometer, and electrical hookup typically last the life of the home with no scheduled service. The fan is the only component that wears out. Continuous-duty radon fans typically run 8 to 12 years before bearing failure or impeller wear reduces airflow below the design target. Replacement fans cost $200 to $400 plus 1 to 2 hours of installation labor.
Homeowners should plan for one or two fan replacements over a typical 20-year residency. Most CDPHE-certified mitigation contractors will return for a replacement at the same hourly rate as the original installation; many maintain customer records and can identify the specific fan model and rebuild kit needed.
Homeowners with questions about an existing system or considering a new installation can reach out through our contact page for a connection to a CDPHE-certified radon mitigation professional.
Common questions about the gas-flow mechanism
Three questions come up consistently when homeowners learn the system redirects rather than destroys radon. The first is whether discharging radon to the outdoor atmosphere creates a hazard for neighbors. Generally no. Outdoor radon disperses rapidly into ambient air; even a fan discharging 100 CFM of soil-gas-laden air produces an immediate downstream concentration that drops below outdoor ambient within 2 to 3 feet of the discharge point. Roof-line termination places the discharge well above any neighboring living space, and natural air movement dilutes the gas quickly.
The second is whether radon dispersed outdoors eventually re-enters the home. The atmosphere is large enough relative to a single mitigation discharge that this is not a practical concern. The radon decays on its 3.8-day half-life regardless, and atmospheric mixing distributes any released volume across thousands of cubic meters within hours.
The third is whether the system removes other indoor air pollutants beyond radon. The answer is mostly no. The system depressurizes the area beneath the slab, which redirects soil-gas including radon and any soil-vapor contaminants present, but it does not address airborne pollutants in occupied living spaces (VOCs, particulate matter, allergens). HRV/ERV ventilation systems address indoor air pollutants more broadly; the radon gas removal system specifically targets the soil-gas entry pathway.
What the system does not do
One useful clarification is what a radon gas removal system does not provide. It does not provide whole-home ventilation. It does not eliminate the source of radon (the underlying uranium decay in soil and bedrock continues indefinitely). It does not protect against radon from secondary sources like well water (radon dissolved in groundwater can off-gas during showering and laundry; this requires a separate water aeration system if levels are elevated). It does not eliminate radon’s daughter products that may already be present in indoor air at installation time; those decay within hours after the entry pathway is shut down, but they are not extracted by the system itself.
Homeowners with well water in elevated-radon regions of Colorado may benefit from a separate water radon test in addition to indoor air testing. The two pathways are independent, and a home with mitigated indoor air radon but high water radon can still produce elevated occupant exposure during routine water use.
References
- EPA radon mitigation system standards — U.S. Environmental Protection Agency
- CDPHE Colorado radon mitigation program — Colorado Department of Public Health and Environment
- American Lung Association radon mitigation resources — American Lung Association
- CDC radon mitigation and lung cancer prevention — Centers for Disease Control and Prevention