A radon mitigation system installation takes 4–8 hours for a single-entry-point job. Most homeowners wake up with elevated radon levels and end the same day with a system running and a measurement 90% lower than before. Here is exactly what happens between those two moments — every step, every decision, every tool, and every material a certified mitigator uses to protect your home.
What Is a Radon Mitigation System?
A radon mitigation system — most commonly an Active Sub-Slab Depressurization (ASD) system — is a mechanical ventilation system that creates negative pressure beneath your home’s concrete foundation. By drawing soil gases (including radon) out from under the slab before they can seep into living spaces, the system routes them safely above the roofline where outdoor air dilutes them to harmless concentrations.
Pre-Installation: Assessment and Planning
Before the crew touches a drill, a properly trained mitigator performs a diagnostic assessment. This is not optional — AARST-ANSI standard SGM-SF requires a pre-mitigation diagnostic to select the appropriate system design.
Site Walkthrough
The mitigator inspects:
- Foundation type: Slab-on-grade, basement, crawl space, or combination
- Slab condition: Cracks, expansion joints, sump pits, drains, and floor penetrations
- Existing ventilation: HRV/ERV systems, exhaust fans, combustion appliances
- Attic accessibility: For interior pipe routing
- Exterior wall access: For exterior routing if attic is not viable
- Electrical availability: Outlet locations within reach of fan placement
Diagnostic Testing: The Core Test
The most critical pre-installation diagnostic is the sub-slab communication test (also called a block test or core test). The mitigator drills a small test hole through the slab — typically 2 inches in diameter — and inserts a vacuum gauge or connects a shop vacuum to assess:
- Sub-slab suction field: How far a vacuum applied at one point extends under the slab
- Aggregate type: Gravel aggregate allows easy airflow; sand or clay-heavy fill may require additional suction points
- Moisture presence: Wet conditions influence pipe placement and fan selection
According to AARST standard SGM-SF Section 5, mitigators must perform this diagnostic to confirm system design before proceeding. A mitigator who skips this step and drills directly is not following best practice.
System Design Selection
Based on the diagnostic, the mitigator selects:
- Number of suction points: Most homes require one; larger slabs or poor aggregate may need two or three
- Fan model: Entry-level (RadonAway RP145), standard (RadonAway RP265), or high-flow (GP501/GP301) based on measured sub-slab airflow resistance
- Pipe routing: Interior through conditioned space to attic (preferred — protects fan from freeze-thaw), or exterior through outside wall (faster installation, fan exposed to weather)
- Pipe diameter: 3-inch PVC for most residential; 4-inch for high-flow applications
Tools and Materials Used in Installation
A professional mitigator arrives with a specific kit. Understanding what they bring helps you verify the job is being done correctly.
Core Tools
- Rotary hammer drill with 3.5–4″ core bit (for slab penetration)
- Reciprocating saw or jigsaw (for wall penetrations)
- Hole saw set (for pipe through walls and plates)
- Shop vacuum (diagnostic testing and debris removal)
- Manometer (magnehelic gauge or digital) for airflow measurement
- PVC pipe cutter or miter saw
- PVC cement and primer
- Caulk gun with polyurethane sealant
- Pipe straps and anchors
- Electrical work tools if hardwired fan
Materials Installed
- 3″ Schedule 40 PVC pipe (typically 8–20 feet depending on routing)
- PVC elbows, tees, couplings
- Radon fan (mounted in attic or exterior)
- System performance monitor (U-tube manometer visible in living space)
- Warning label (required by AARST standards)
- Weatherproof exterior cap (termination above roofline or 12″ above grade on exterior)
- Concrete patch or hydraulic cement (sealing core hole perimeter)
Step-by-Step Installation: Interior Routing (Most Common)
Interior routing — pipe runs inside the home through conditioned space up to an attic-mounted fan and exterior discharge — is the most durable and recommended approach per AARST SGM-SF guidelines.
Step 1: Mark and Core the Slab (15–30 Minutes)
The mitigator selects the suction point location — typically a utility closet, mechanical room, or unfinished basement corner — and uses a rotary hammer with a 3.5″ or 4″ core bit to drill through the concrete slab. This hole becomes the suction pit connection. Debris is vacuumed out and the hole is temporarily covered while work continues.
The mitigator may use a shop vacuum at the fresh core hole to conduct a final suction field confirmation before cutting any additional material.
Step 2: Prepare Sub-Slab (5–15 Minutes)
If aggregate (gravel) is present below the core, the technician may use a long-handled tool to redistribute material and maximize the suction cavity radius. If there is no aggregate (just compacted soil or clay), additional suction points may be required — this is identified in the diagnostic phase, not discovered mid-installation.
Step 3: Install the Riser Pipe (30–90 Minutes)
A 3″ Schedule 40 PVC pipe — the riser — connects from the slab core hole, routes up through the interior of the home, and terminates above the roof. The routing path depends on the home’s framing:
- Closet routing: Pipe runs vertically through a closet wall, through the top plate into the attic
- Utility chase routing: Existing utility chases (HVAC, plumbing) may offer natural routing paths
- Garage wall routing: Common in slab homes with attached garages
All joints are cemented with PVC primer and cement. The pipe is strapped to framing members every 4–6 feet per standard plumbing practice. Where the pipe passes through fire-rated assemblies (floor/ceiling), fire-rated caulk is required by local building codes.
Step 4: Mount the Radon Fan (30–60 Minutes)
The radon fan is installed in the attic — between the riser from below and the discharge pipe to the exterior. Fan mounting requirements per AARST SGM-SF:
- Fan must be installed in unconditioned space (attic, garage, or exterior) — never in conditioned living space or basement. This ensures that if the fan housing develops a leak, radon-laden air is not discharged inside the home.
- Fan should be accessible for inspection and future replacement
- Fan wiring connects to a dedicated circuit or outlet within reach; some installations use a junction box with a switched outlet, others hardwire to the panel
Common fan models installed:
- RadonAway RP145: Low-static, low-flow — ideal for homes with excellent sub-slab aggregate. Draws ~40 CFM at 0.5″ WC.
- RadonAway RP265: Mid-range — the most commonly installed residential fan. Draws ~75 CFM at 0.5″ WC.
- RadonAway GP501: High-static, high-flow — for homes with dense fill, clay soils, or multiple suction points.
- Festa DP3: An alternative brand used by some contractors; similar performance range to RP265.
Step 5: Install the Discharge Pipe (15–30 Minutes)
From the fan, a discharge pipe routes radon-laden air out of the attic and above the roofline. AARST SGM-SF requires the discharge termination to:
- Extend at least 12 inches above the highest eave of the roof (or above any window/door within 10 feet)
- Terminate with a weatherproof cap to prevent rain/debris entry
- Not terminate within 10 feet horizontally of a window, door, or operable vent
The discharge pipe typically penetrates the roof via a standard plumbing pipe flashing boot or exits through the gable end. Both are acceptable; gable exit is faster and avoids roof penetration.
Step 6: Seal the Slab Penetrations (15–30 Minutes)
Sealing is a critical but frequently underemphasized step. The mitigator uses hydraulic cement or non-shrink epoxy grout to seal the annular gap around the riser pipe at the slab. Polyurethane caulk seals any visible cracks in the slab, expansion joints, and any floor-wall joints in the mitigation zone.
Why sealing matters: every unsealed gap is a path for radon to bypass the sub-slab vacuum and enter the home directly, reducing system effectiveness. A system with excellent fan performance but poor sealing can underperform significantly compared to a well-sealed system with a smaller fan.
Step 7: Install the System Performance Monitor (5–10 Minutes)
The mitigator installs a U-tube manometer — a small liquid-filled gauge — in the riser pipe at a visible interior location, typically at the base of the riser in a utility closet or at eye height in a basement. This monitor shows whether the system is operating:
- Liquid displaced (column imbalanced): System generating negative pressure — operating normally
- Liquid level (column balanced): System has stopped generating negative pressure — fan may be off or failed
AARST SGM-SF Section 9 requires a performance indicator on every installed system. This monitor is the homeowner’s first alert that the fan needs attention.
Step 8: Label the System and Power On (5 Minutes)
AARST standards require a permanent warning label on the pipe indicating:
- “RADON REDUCTION SYSTEM — Do not cover or obstruct”
- Installer contact information and license number
- Installation date
- Fan model and serial number (on the fan body itself)
The fan is powered on. The mitigator confirms airflow with the manometer and may use a digital gauge to measure the actual static pressure the fan is generating at the suction point.
Post-Installation Verification
A complete installation includes a post-installation check and documentation.
System Performance Measurement
The mitigator measures and records:
- Static pressure at the suction point (in inches of water column)
- Airflow rate (CFM) — confirmed by digital anemometer at the discharge termination or calculated from pressure curves
- Fan model and serial number
- Number of suction points and their locations
Post-Installation Radon Testing
The system itself does not produce an immediate radon reading you can verify that day. EPA and AARST recommend waiting at least 24 hours after installation before placing a post-mitigation test device, and the test should run for a minimum of 48 hours (short-term charcoal test) under closed-house conditions.
Most mitigators either include a post-mitigation test in their package or provide a short-term test kit at installation. Results typically come back within 3–7 business days. Target: below 4.0 pCi/L (EPA action level). Most properly installed systems achieve 0.5–2.0 pCi/L in homes that previously tested 4–20 pCi/L.
Installation Documentation
The mitigator should provide you with a written report including:
- Pre-mitigation radon level
- System type installed
- Fan model, serial number, and manufacturer warranty information
- Suction point location(s)
- System pressure readings
- Post-installation test kit instructions
- State contractor license number and certification credentials (NRPP or NRSB)
- Workmanship warranty terms (typically 1–5 years)
Keep this documentation. Real estate disclosure often requires it when you sell the home.
What to Watch for During Installation
Being present during installation (or reviewing work afterward) lets you spot quality issues before they become problems.
Green Flags
- Mitigator performs a diagnostic test before drilling
- Fan is located in attic or exterior — not inside a living space
- All PVC joints are primed and cemented (not just press-fit)
- Slab gap around riser pipe is patched with hydraulic cement, not just foam
- U-tube manometer installed at visible location
- Required labeling is applied to the pipe
- Mitigator records and provides pressure/flow measurements
- Post-mitigation test kit included or scheduled
Red Flags
- No diagnostic test — mitigator drills immediately without testing sub-slab conditions
- Fan installed in conditioned living space (basement, utility room inside the thermal envelope)
- PVC joints dry-fitted without cement
- Slab gap sealed only with spray foam (foam compresses over time and is not airtight)
- No manometer — “just check the fan is running”
- No documentation provided
- Discharge terminates into attic space, crawl space, or below eave level
Exterior Routing: The Faster Alternative
When interior routing is impractical — no attic access, finished interior walls, or homeowner preference for speed — mitigators run the pipe on the exterior of the home. The installation sequence is identical except:
- The pipe penetrates through the foundation wall or rim joist directly to the exterior
- The fan is mounted on the exterior wall in a weatherproof location
- The discharge pipe runs up the exterior wall, terminating above the roofline or at least 12 inches above the highest point of the adjacent structure
Exterior routing typically adds 60–90 minutes in pipe paint and weatherproofing, but saves time on interior framing penetrations. The trade-off: exterior fans are exposed to freeze-thaw cycles and weather, reducing fan lifespan slightly compared to attic-mounted fans in temperature-controlled environments.
How Long Does Radon Mitigation Installation Take?
For a standard single-suction-point ASD system:
- Simple slab, interior routing, accessible attic: 3–4 hours
- Basement with finished walls, complex routing: 5–7 hours
- Multiple suction points: Add 1–2 hours per additional point
- Crawl space sub-membrane systems: 4–8 hours depending on coverage area
- New construction passive-to-active upgrade: 1–2 hours (pipe already installed)
Frequently Asked Questions
How does a radon mitigation system work after installation?
The fan runs continuously (24/7/365) at low wattage — typically 20–90 watts, similar to a light bulb. It draws radon-laden soil gas out from under the slab and discharges it above the roofline where it disperses into the atmosphere. Operating cost is typically $30–$75 per year in electricity depending on fan model and local utility rates.
Can I be home during radon mitigation installation?
Yes. There is no requirement to vacate. The work generates concrete dust during the core drilling step — a good mitigator uses a vacuum simultaneously to minimize dust. If you have respiratory sensitivities, briefly stepping outside during the core drilling (5–10 minutes) is reasonable.
How long does it take for a radon mitigation system to work?
The system begins reducing radon immediately when the fan is turned on. Most of the reduction occurs within the first few hours. However, because radon levels fluctuate naturally with barometric pressure, temperature, and soil moisture, a formal post-mitigation test requires 48 hours of operation under closed-house conditions to produce a reliable average.
What if the radon level is still high after installation?
Post-mitigation tests that still read above 4.0 pCi/L require a callback. Common causes: insufficient suction field coverage (additional suction point needed), unsealed pathways (cracks, sump, floor drain), fan is undersized for the specific aggregate conditions, or the test was conducted under non-standard conditions. A reputable mitigator will address these under their workmanship warranty at no additional charge.
Do I need to do anything after the system is installed?
Check the U-tube manometer monthly — the liquid column should remain displaced. Conduct a post-mitigation radon test within 30 days of installation. Then retest every 2 years per EPA recommendations, or any time you make structural changes to the foundation, finish a basement, or notice the manometer reading has changed.
Does the installation require a permit?
Permit requirements vary by municipality. Some jurisdictions require a building permit for any new mechanical penetration through the foundation or roof. A certified mitigator should know the local requirements and obtain permits where required. Unpermitted work can complicate home sales, particularly in states with radon disclosure laws.
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