A radon mitigation system has six primary components and several secondary ones. Each serves a specific function in the chain from soil gas collection to safe discharge above the roofline. Understanding what each part does — and what failure looks like — turns a mysterious pipe in your basement into a system you can actually monitor and maintain.
Component 1: The Suction Point
The suction point is where the mitigation system makes contact with the radon source. It is the entry point for the entire system — everything else serves only to move radon from here to outside.
In Slab and Basement Homes (ASD)
A 3.5″–4″ diameter core hole drilled through the concrete slab, penetrating into the sub-slab aggregate or soil layer beneath. The riser pipe seats directly into this hole. Around the pipe, the annular gap is sealed with hydraulic cement to prevent uncontrolled air entry at the penetration point.
The sub-slab aggregate — typically 3/4″ clean gravel installed during construction — is the reservoir from which the fan draws. The aggregate allows pressure to distribute laterally, so a single suction point can depressurize a large area. Homes with poor aggregate (clay, sand fill) have limited pressure distribution and may require multiple suction points.
In Crawl Space Homes (ASMD)
The suction point penetrates through the vapor barrier membrane and connects to a perforated collection mat placed beneath it. The mat creates an air gap between the soil and the membrane, allowing the fan to draw from a distributed area rather than a single point. Multiple suction points connected via manifold pipe are common in crawl space systems.
Sump Pit Integration
When a sump pit is present, the pit itself serves as a highly effective suction point. An airtight lid replaces the standard pit cover, with a pipe fitting connecting the pit to the fan system. The drain tile network surrounding the foundation perimeter communicates with the sump, creating a distributed collection network that can cover the entire foundation footprint from a single connection.
Component 2: The Riser Pipe
The riser pipe is the vertical backbone of the system — 3-inch or 4-inch Schedule 40 PVC that carries radon-laden soil gas from the suction point at the slab up to the fan location in the attic or on the exterior wall.
Pipe Specifications
- Material: Schedule 40 PVC — the same material used for residential drain, waste, and vent (DWV) plumbing
- Diameter: 3″ for most residential installations; 4″ for high-flow applications or when the diagnostic test shows high static pressure requirements
- Joints: All joints made with PVC primer and solvent cement — never dry-fitted. A dry-fitted joint will eventually separate or allow air to bypass the system.
- Slope: Pipe should have positive slope toward the suction point (condensate drains back to the sub-slab rather than pooling in the pipe)
- Strapping: Secured to framing with pipe hangers every 4–6 feet; pipe should not flex or vibrate during fan operation
Routing Paths
The riser pipe takes one of two primary paths from slab to fan:
- Interior routing: Pipe runs through the home’s interior — through a wall cavity, utility chase, or closet — to the attic. The fan is mounted in the attic, protected from weather. This is the preferred approach for fan longevity and noise isolation.
- Exterior routing: Pipe penetrates through the foundation wall or rim joist directly to the exterior, running up the outside of the home. Faster to install and avoids interior framing work, but the fan is exposed to weather and temperature extremes.
Component 3: The Radon Fan
The radon fan is the active heart of the system. It creates continuous negative pressure in the pipe network, drawing radon-laden air from the sub-slab and routing it to discharge.
Fan Placement Rules
AARST-ANSI SGM-SF has an absolute requirement: the fan must be installed in unconditioned space (attic, exterior, or garage) — never in conditioned living space, including finished basements and utility rooms inside the thermal envelope. The reason: radon fan housings can develop minor leaks over time. If the fan leaks in conditioned space, radon enters the home at the leak point. In unconditioned space, any leak discharges into air that is not routinely occupied.
Common Fan Models
- RadonAway RP145: 20W, ~40 CFM at 0.5″ WC. Lowest energy use; ideal for excellent aggregate, small footprint, or homes with measured low static pressure at the suction point.
- RadonAway RP265: 55W, ~75 CFM at 0.5″ WC. The most-installed residential radon fan in the U.S. Covers the majority of single-family residential conditions.
- RadonAway GP301/GP501: 85–90W. High-static fans for demanding conditions: dense sub-slab fill, large footprints, multiple suction points, or unusually deep aggregate requiring high lift.
- Festa DP3: Alternative brand in the RP265 performance class, used by some contractors.
Fan Sizing Logic
Fan selection is determined by the pre-installation diagnostic test — specifically the measured static pressure at the suction point under test vacuum conditions. A mitigator who selects a fan without performing a diagnostic test is guessing. Oversized fans consume unnecessary electricity and can over-depressurize the sub-slab (drawing conditioned air into the soil, increasing heating costs). Undersized fans leave radon reduction incomplete.
Fan Lifespan and Warranty
RadonAway fans carry a 5-year manufacturer warranty. Expected operational lifespan is:
- Interior/attic-mounted fans: 10–15 years
- Exterior-mounted fans: 7–12 years (weather exposure shortens bearing life)
Fan replacement is the most common maintenance event in a radon system’s life. Because the pipe network and all fittings remain in place, a fan replacement is typically a 30–60 minute job costing $100–$300 in labor plus the replacement fan ($80–$200).
Component 4: The Discharge Pipe and Termination Cap
From the fan outlet, a discharge pipe routes the extracted radon above the roofline and terminates with a weatherproof cap. This is where radon exits the system and disperses into the atmosphere.
Termination Requirements (AARST SGM-SF)
- Discharge must extend at least 12 inches above the roof surface at the penetration point
- Discharge must not terminate within 10 feet horizontally of any window, door, or mechanical ventilation opening
- Termination cap must prevent precipitation entry and pest intrusion while allowing free airflow
- For exterior-routed systems: discharge must terminate above the roof eave line — not at the side of the house below the eave
Roof vs. Gable Discharge
Discharge can exit through the roof (via a plumbing pipe boot flashing) or through the gable end of the attic. Gable discharge is preferred by many contractors because it avoids a roof penetration — reducing the potential for future leak points and typically faster to install. Both are compliant when termination height requirements are met.
Component 5: The System Performance Indicator (Manometer)
The U-tube manometer is the system’s dashboard — the only component visible inside the living area that tells you whether the system is operating correctly without requiring a radon test.
How the Manometer Works
The U-tube manometer is a small glass or plastic tube filled with colored liquid, installed on the riser pipe at a visible interior location. It connects to the inside of the pipe via a small fitting. When the fan is running and creating negative pressure:
- Liquid displaced (one side higher than the other): Fan is generating suction — system operating normally
- Liquid level (both sides equal): Fan is not generating suction — fan may be off, failed, or the pipe has a breach
AARST SGM-SF requires a performance indicator on every active system installation. Check it monthly.
Digital Pressure Gauges
Some installations use a digital magnehelic gauge instead of a liquid U-tube, providing a numeric pressure reading in inches of water column. These are more precise but add cost ($30–$80 vs. $5–$15 for a U-tube). Both are AARST-compliant performance indicators.
Component 6: Sealing and Caulk
Sealing is not a glamorous component, but it is frequently the difference between a system that achieves 95% reduction and one that achieves 70%. Every unsealed gap in the slab, wall joint, or floor penetration is a pathway for radon to bypass the sub-slab vacuum and enter the home directly.
Sealing Materials Used
- Hydraulic cement or non-shrink epoxy grout: Used to seal the annular gap around the riser pipe at the slab core hole. Sets hard and does not compress over time. The correct material — spray foam is NOT appropriate for this application (foam compresses).
- Polyurethane caulk: Used to seal expansion joints, control joints, visible cracks, and the floor-wall perimeter joint. More flexible than hydraulic cement — accommodates minor foundation movement.
- Backer rod: Foam rod inserted into wide joints before caulking, to provide backing and reduce the volume of caulk required for deep gaps.
- Rigid foam board: Used to seal foundation vents in crawl space ASMD systems.
- Fire-rated caulk: Required where the pipe passes through fire-rated floor/ceiling assemblies per local building code.
Required Labeling
AARST standards require a permanent warning label applied to the riser pipe at a visible location. The label identifies the pipe as a radon reduction system and includes:
- “RADON REDUCTION SYSTEM — Do not cover or obstruct”
- Installer name and state license/certification number
- Installation date
- Fan model (typically noted on the fan body itself)
This label serves homeowners, future buyers, home inspectors, and any contractor who works on the home after installation. A system without a label is a system that has no installation record attached to it — a flag during real estate transactions in states with radon disclosure requirements.
Frequently Asked Questions
What does the pipe sticking out of my basement floor connect to?
The pipe connects to a core hole drilled through the concrete slab, which opens into the aggregate or soil layer beneath your foundation. This is the suction point — the pipe draws radon-laden soil gas from beneath the slab and routes it up through the home to a fan in the attic, then discharges it above the roofline.
What is the liquid-filled gauge on my radon pipe?
That is the U-tube manometer — the system’s performance indicator. The colored liquid in the tube should be displaced (one side higher than the other) when the system is running correctly. A level liquid column means the fan is not generating suction and should be inspected.
Why does the fan need to be in the attic and not the basement?
AARST standards require the fan to be in unconditioned space — never in conditioned living area. If the fan housing develops a minor leak, radon discharges into unconditioned space (attic, exterior) rather than into the living area. This is a safety requirement, not a preference.
How many suction points does a radon system need?
Most slab and basement homes with good aggregate need one. Larger footprints (3,000+ sq ft), poor sub-slab fill (clay, sand), or complex foundation geometry may need two or three. Crawl space systems typically need two to four. The pre-installation diagnostic test determines the correct number — a mitigator should not determine suction point count without testing first.
What should I check on my radon system each month?
Check the U-tube manometer — confirm the liquid column is displaced, indicating the fan is generating suction. Listen for the fan (a faint hum from the attic area is normal; silence or new grinding sounds are not). Visually confirm the pipe labels and required signage are still in place. Conduct a post-mitigation radon test every 2 years per EPA recommendations.
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