What Is a Radon Reduction System: Components Walkthrough
A radon reduction system is the engineered apparatus installed in a home to lower indoor radon concentrations to safe levels. The system goes by several names — radon mitigation system, radon remediation system, sub-slab depressurization system — but the physical hardware is essentially the same across naming conventions. This guide breaks down the system by its individual components: what each part is, what it does, how it is installed, and how to evaluate quality of installation. The aim here is to give homeowners enough technical vocabulary to read a mitigation bid intelligently and identify a competent installation. This guide summarizes EPA RMS-LL guidance current as of 2026 — consult a state-licensed mitigation professional for system design and an EPA-listed measurement professional for testing decisions.
What Is a Radon Reduction System?
A radon reduction system is a permanent installation in a residential building that continuously reduces indoor radon concentration by creating a low-pressure zone beneath the foundation. Soil gas, including radon, migrates into the suction system rather than into living space, and the collected gas is exhausted above the roof line. The system runs 24 hours a day, every day, for the life of the building. EPA’s Radon Mitigation Standards for Low-Rise residential buildings (RMS-LL) define the design and performance requirements; the system shape that meets those requirements is known as active sub-slab depressurization (ASD).
Effective systems reduce indoor radon by 50% to 99% from pre-mitigation levels. Most Front Range installations bring concentrations below 2 pCi/L from starting levels of 8 to 20 pCi/L. Our broader radon testing guide for Front Range homeowners covers when reduction is needed in the first place. Our companion piece on radon mitigation options covers the strategy-level choices that lead to system design.
Component 1: PVC Pipe
The vent pipe is the spine of the system. Schedule 40 PVC pipe (typically 3 to 4 inches in diameter) carries soil gas from the suction point beneath the slab to the exhaust termination above the roof. Pipe is joined at every connection with primer and PVC cement, and the joints must be solvent-welded — not slip-fit or threaded — because the system must hold a small negative pressure continuously.
Pipe Sizing
The 3- to 4-inch nominal diameter is not arbitrary. Smaller pipe creates flow resistance that wastes fan capacity; larger pipe is more expensive without proportional benefit. The 4-inch size is standard in newer installations; 3-inch installations are common in older retrofits.
Pipe Routing
Pipe routing should minimize horizontal runs (which collect condensation) and maximize visibility for inspection. Pipe should be supported by clamps every 5 to 10 feet, sloped slightly back toward the suction point to allow any condensation to drain back, and pass through unconditioned spaces wherever practical. Pipe penetrations through the building envelope must be sealed at every point.
Component 2: Suction Point
The suction point is where the system connects to the soil-gas reservoir beneath the foundation. A hole is drilled through the concrete slab — typically 3 to 6 inches in diameter — and a small pit is excavated beneath the slab to create a collection chamber. The pipe is inserted into the hole and sealed at the slab-pipe junction with polyurethane sealant or non-shrink concrete.
The pit beneath the slab is important. Without it, the suction is limited to the small area immediately around the pipe end. With it, suction propagates outward through the gravel layer (or permeable soil) beneath the slab, covering a much larger footprint. A typical pit is 12 to 24 inches in diameter and 6 to 12 inches deep.
Component 3: Inline Fan
The fan is the active element of the system. It creates the negative pressure (suction) that drives soil gas into the pipe rather than into living space. Residential fans are typically inline centrifugal units rated 50 to 90 watts, drawing 0.5 to 1 amp at 120 volts. The fan operates continuously.
Fan Location
EPA RMS-LL requires the fan to be mounted in unconditioned space — typically the attic, garage, or exterior wall. The location rule exists for safety: if the fan housing or downstream pipe develops a leak, soil gas should not enter living space. Fan mounting in a basement or living area is non-compliant with the standard.
Fan Sizing
The right fan depends on the soil permeability and the number of suction points. Fans are characterized by their pressure-flow curve. A higher-pressure fan is required for low-permeability soils (clay, dense fill); a higher-flow fan is required for highly permeable soils (gravel). Most Front Range homes use a mid-range fan; complex installations may use multiple fans or larger units. Resources from epa.gov/radon list certified professionals who size fans correctly.
Component 4: Manometer
The manometer is the homeowner’s visible confirmation that the system is running. It is a simple U-tube pressure gauge containing colored fluid (typically a dyed alcohol or water). One side connects to the vent pipe through a tee fitting; the other side opens to atmosphere. The pressure differential created by the fan offsets the fluid columns by a measurable amount, typically 0.5 to 2.0 inches of water column.
The gauge should be mounted on the pipe at eye level in an accessible location — typically near where the pipe enters the conditioned space, or in a utility room. A monthly glance at the manometer confirms the fan is operating. Equal fluid columns indicate fan failure; offset columns indicate a working system.
Component 5: Sealed Sump Cover and Floor Drains
Sealing is integral to system effectiveness. The most important sealing point is the sump pit cover, which provides a direct soil-to-interior pathway when unsealed. A radon-rated sump cover with a one-way pressure relief valve seals the pit while still allowing emergency overflow if the sump pump fails.
Floor Drains
Floor drains in basement slabs connect directly to soil. They should be fitted with a trap primer or a one-way trap cover to prevent soil gas from flowing up through the drain.
Slab Cracks
Visible cracks in the basement slab should be sealed with elastomeric caulk or polyurethane sealant. Hairline cracks are not material; cracks wider than 1/16 inch should be addressed. Sealing reduces the air loss that otherwise short-circuits fan suction.
Component 6: Electrical Wiring and Code Compliance
The fan requires a dedicated 120-volt circuit. Electrical work must comply with the local jurisdiction’s adopted electrical code — typically the National Electrical Code as referenced by the International Residential Code. Most installations include:
- A dedicated breaker at the panel.
- An exterior-rated junction box if the fan is on an outside wall.
- A pilot light or alarm circuit that visibly indicates power to the fan.
- Optional: a battery-backup power supply for the fan to operate during short outages.
The electrical installation should be performed by a licensed electrician if local code requires it. Many mitigation contractors employ electricians on staff or subcontract the electrical scope. Our piece on radon reduction system design covers the full electrical scope in additional detail.
Component 7: Roof Exhaust Termination
The pipe must terminate above the roof line at a height and distance specified by EPA RMS-LL. The standard requirements:
- Terminate at least 12 inches above the roof surface.
- Locate at least 10 feet from any window, door, or air intake on the same building.
- Locate at least 10 feet from any window or air intake of a neighboring building when possible.
- Cap with a rain cap or weather flange to prevent water ingress without restricting airflow.
The roof termination is the point at which soil gas re-enters the atmosphere. By the time the gas disperses a few feet from the pipe outlet, the concentration has dropped to near-outdoor background levels.
How the Components Work Together
The integrated system operates by creating a continuous pressure differential. The fan pulls air from the pipe; the pipe draws from the suction point; the suction point draws from the soil beneath the slab through the excavated pit. The sealed sump cover, floor drains, and slab cracks reduce the air “leakage” that would otherwise let the fan short-circuit through these openings instead of pulling from the soil.
When the system is properly designed, soil gas flows from the surrounding soil into the suction system rather than upward into the building. The manometer shows the pressure differential is present. The roof exhaust disperses the collected gas above the roof line. The home tests below the EPA action threshold (4.0 pCi/L) and stays there as long as the fan continues running.
Post-Installation Verification
EPA RMS-LL requires post-installation radon testing to confirm the system has achieved the target level. The standard approach:
- Allow the system to operate for at least 24 hours after commissioning.
- Place a short-term test kit in the lowest livable level of the home for 48 to 96 hours.
- If the result is below 4 pCi/L, the system passes commissioning.
- If the result is still elevated, the system requires troubleshooting — typically larger fan, additional suction points, or sealing improvements.
Post-mitigation testing is a homeowner’s evidence that the installed system performs as designed. The result should be documented and retained with the home’s permanent records.
Ongoing Maintenance
An installed system requires minimal but regular attention:
- Monthly manometer check. A glance confirms the fan is running.
- Annual visual inspection. Walk the pipe routing to check for cracks, loose joints, or condensation.
- Periodic re-testing. Every 2 to 5 years and after any foundation work, major renovation, or HVAC change.
- Fan replacement. Every 10 to 20 years at $250 to $500 cost.
The system is designed to operate transparently — once installed, it requires almost no attention beyond the periodic checks above. The protective benefit continues for the life of the building.
How to Read a Manometer Reading
The U-tube manometer is the simplest diagnostic tool in the system. When the fan is operating correctly, the colored fluid in the U-tube is offset between the two columns by a measurable amount — typically 0.5 to 2.0 inches of water column. The offset reflects the negative pressure the fan creates in the pipe relative to ambient atmospheric pressure. Higher offset means stronger suction; lower offset means weaker suction or restricted airflow.
Equal fluid columns indicate the fan has stopped or the pipe is blocked. Either condition requires immediate attention because indoor radon levels can return to pre-mitigation values within days of fan failure. Sudden large changes in the reading (the fluid columns become much closer together or much farther apart than they were the previous month) suggest something has changed in the system — a fan that is wearing out, a partial pipe blockage, a leak in the pipe joint, or a change in soil-gas dynamics.
Some installations include a digital pressure sensor with an audible alarm in addition to the manometer. The alarm triggers if pressure falls below a threshold for a set duration. These add-ons cost an additional $100 to $300 at installation and provide more immediate feedback than the visual manometer alone. For homeowners who travel frequently or have absentee management of the property, the alarm option is worth considering.
Electrical Consumption and Cost
An inline fan rated 50 to 90 watts operates continuously, which translates to about 440 to 790 kilowatt-hours per year. At Front Range electricity rates of $0.10 to $0.15 per kWh, the annual electricity cost is roughly $44 to $118 for the radon mitigation system. This is comparable to a small refrigerator. The cost is the price of continuous radon protection and is built into the homeowner’s ongoing utility expense rather than appearing as a separate line item.
Fan efficiency has improved over the past decade. Newer ECM (electronically commutated motor) fans use less power than older shaded-pole motors while delivering equivalent or better airflow. Replacing a 10-year-old fan with a current-generation ECM model typically reduces electricity consumption by 25% to 40%. The replacement also extends expected fan life — newer fans often last 15 to 20 years rather than the 10 to 15 years typical for older models.
Integration With Smart-Home and Monitoring Tools
Some installed systems now integrate with smart-home platforms via Wi-Fi-enabled monitors. A continuous radon monitor placed in the home transmits real-time concentration data to a smartphone app, alerting the homeowner if levels rise above a threshold. Wi-Fi-enabled pressure sensors on the vent pipe can alert if fan operation changes. These additions cost $200 to $500 and are particularly valuable for vacation homes, rental properties, or any installation where the homeowner cannot easily check the manometer in person.
The integration is optional. A basic system without smart-home connectivity provides full radon protection as long as the homeowner performs the routine monthly visual checks. The smart-home additions provide convenience and earlier failure detection rather than fundamentally different protection.
References
- EPA Consumer’s Guide to Radon Reduction — U.S. Environmental Protection Agency
- Colorado Radon Program — Colorado Department of Public Health and Environment
- CDC Radon Health Information — Centers for Disease Control and Prevention
- American Lung Association Radon Resources — American Lung Association
Front Range homeowners considering installation can reach out to a vetted local inspector to coordinate testing and discuss the right system design for the home’s foundation type.