How To Install A Radon Mitigation System: A Technical Step-by-Step Guide

Installing an active sub-slab depressurization radon mitigation system requires sealing all foundation entry points, drilling a suction pit through the concrete slab, routing a continuous 3-inch or 4-inch Schedule 40 PVC vent pipe to an inline radon fan, and venting exhaust gases safely above the roofline. This process alters pressure differentials to redirect cancer-causing soil gases away from the living space, targeting a post-mitigation radon level below the EPA action limit of 4.0 pCi/L.

Pre-Installation Engineering & Material Diagnostics

Before initiating the installation of an active sub-slab depressurization (SSD) system—the most common and effective method for reducing indoor radon—you must execute diagnostic planning. This begins with a continuous radon monitor (CRM) test or short-term charcoal canisters to establish your baseline radon levels. Additionally, you must perform a sub-slab communication test (also known as a pressure field extension test) by drilling a small diagnostic hole in the slab, applying a vacuum to it, and measuring pressure drops at distant test holes using a micro-manometer. This ensures your proposed extraction point can draw air from across the entire foundation.

Equipment, Materials, and Planning Metrics

• Required Power Tools and Safety Gear:
  
  
  • Rotary hammer drill with a 5-inch diamond-tipped core bit and 1/2-inch masonry bits
  • Reciprocating saw or PVC pipe cutter
  • Personal Protective Equipment (PPE): N95 or HEPA respirator (critical for concrete/silica dust protection), safety glasses, and heavy-duty work gloves
• Essential System Materials:
  
  
  • Inline radon fan (e.g., Fantech HP 2190 or GP 501, selected based on soil density)
  • Schedule 40 PVC pipe (3-inch or 4-inch diameter) and compatible 90-degree sweep elbows
  • Flexible, vibration-damping rubber couplings (Fernco style) with stainless steel hose clamps
  • Polyurethane elastomer sealant (specifically rated for concrete, such as ASTM C920 compliant caulking)
  • U-tube manometer (0-3 inch water column scale) to monitor system vacuum pressure
• Performance Metrics and Project Scope:
  
  
  • Estimated Budget: $350 to $700 for raw materials and tools (compared to $1,500 to $3,000 for professional installation)
  • Project Duration: 6 to 10 hours of active labor depending on slab hardness and pipe routing complexity
  • Compliance Target: Safe mitigation below the EPA action level of 4.0 pCi/L, with an ideal target below 2.0 pCi/L

Step-by-Step Active Sub-Slab Depressurization Installation

Step 1: Selecting and Coring the Extraction Point

Selecting the optimal location for the suction point is critical. It must be positioned in a utility area, closet, or basement corner where you can route the PVC pipe vertically through the home's framing (or along an exterior wall) without disrupting living spaces. Avoid structural footings, load-bearing walls, and under-slab plumbing utility runs.

To begin, place your rotary hammer drill equipped with a 5-inch diamond core bit perpendicular to the concrete slab. Apply steady downward pressure while drilling, occasionally spraying a fine mist of water to suppress hazardous crystalline silica dust. Once the core bit cuts entirely through the 4-inch slab, carefully extract the concrete plug using a pry bar or heavy-duty pliers.

Warning: Always locate underground utilities, post-tension cables, and main sewer drain lines before drilling into any concrete slab. Damaging a post-tension cable can compromise the structural integrity of your foundation.

Step 2: Excavating the Sub-Slab Suction Pit

The air space created immediately below the slab dictates the vacuum reach of your fan. With the concrete plug removed, you will find dirt, sand, clay, or gravel aggregate.

Using a hand trowel, soil auger, and a heavy-duty shop vacuum, excavate approximately 5 to 10 gallons of soil (roughly 1 to 1.5 cubic feet) from beneath the concrete hole. Digging a wide, bowl-shaped pit directly beneath the slab exposes more aggregate surface area. This physical void reduces air flow resistance, allowing the radon fan to draw soil gas from the entire sub-slab footprint rather than pulling air from only a tight, localized pocket.

Step 3: Fabricating and Sealing the Suction Pit Interface

Insert a straight length of Schedule 40 PVC pipe into the newly dug pit. The pipe should extend approximately 1 to 2 inches below the bottom of the concrete slab, ensuring it does not touch the soil at the bottom of the pit, which would restrict airflow.

Wrap a layer of closed-cell backer rod tightly around the outer diameter of the PVC pipe where it intersects the slab. Push the backer rod 1 inch down into the circular gap between the pipe and the concrete.

Apply a generous bead of premium, non-sag polyurethane sealant over the backer rod, tooling it smooth against the concrete and the pipe wall. This polyurethane seal must be completely airtight; any leakage here will draw conditioned air out of your basement, reducing system efficiency and wasting energy.

Step 4: Routing the PVC Vent Piping

Route the PVC vent pipe from the suction point to the location where the inline radon fan will be mounted. When routing, you must maintain a slope of at least 1/8-inch of drop per foot of horizontal run back toward the suction pit. This slope allows any condensation that forms inside the cold pipe to drain back into the soil beneath the slab, preventing water from pooling inside the line and choking off airflow or destroying the fan motor.

Use high-quality PVC primer and heavy-duty PVC cement on all joints. Secure the pipe runs to floor joists and wall studs using robust pipe hangers spaced no more than 6 feet apart on horizontal runs and 8 feet apart on vertical runs.

Pro-Tip: Do not use standard 90-degree elbows on horizontal-to-vertical transitions. Instead, use "long sweep" 90-degree elbows or two 45-degree elbows. This reduces friction loss, maximizes velocity, and minimizes structural air-flow noise.

Step 5: Positioning and Mounting the Inline Radon Fan

By building code and safety design standards (AARST/ANSI), the inline radon fan must never be installed within a conditioned or occupied indoor living space, basement, or crawlspace. If the fan or its fittings develop a leak, it would discharge concentrated radon gas directly into the home.

The fan must be located in an unoccupied attic space, an unconditioned garage attic, or mounted on an exterior wall of the home. Mount the fan vertically to prevent condensation from pooling in the housing.

Connect the fan to the PVC intake and exhaust pipes using flexible rubber couplings (Fernco couplers) secured with stainless steel hose clamps. These rubber couplers insulate the house from fan motor vibrations and allow for easy fan replacement in the future.

The electrical connection must comply with local codes: wire the fan to a dedicated electrical box with a nearby outdoor or attic weather-proof service disconnect switch.

Step 6: Installing the Exhaust Stack Termination

Extend the exhaust PVC pipe from the discharge side of the inline fan upward to its termination point. The exhaust outlet must terminate at least 12 inches above the roofline to prevent snow blockage, at least 10 feet above ground level, and at least 10 feet away (horizontally or vertically) from any window, door, skylight, or mechanical air intake. This prevents exhausted radon gas from re-entering the home through convective air currents.

Do not install a rain cap on the top of the exhaust pipe, as it can trap moisture, cause freezing issues, and restrict upward exhaust velocity. Instead, leave the pipe open to the sky; rain falling down the vertical pipe will safely pass through the fan and drain back into the sub-slab soil.

Step 7: System Activation and Manometer Calibration

Mount the U-tube manometer on the main vertical run of the PVC pipe in a highly visible location, such as a basement utility room.

Drill a small 3/16-inch hole into the PVC pipe approximately 6 inches above the top of the manometer. Insert the vinyl static pressure tube from the manometer into this hole, sealing the insertion point with a small rubber grommet or silicone.

Zero the manometer scale, then turn on the power to the inline radon fan. The suction created by the fan will draw the colored fluid up on the side connected to the pipe. Note this reading; a standard system should show a system vacuum level between 0.5 and 2.0 inches of Water Column (WC).

Write the baseline reading, date, and installer name on a system label affixed directly next to the manometer.

Sub-Slab Aggregate & Fan Performance Matrix

Selecting the proper fan and pipe configuration depends entirely on the soil aggregate permeability under your concrete slab. Use the reference matrix below to match your home's soil conditions with the correct system components.

System Diagnostics, Common Pitfalls, & Field Fixes

When a newly installed radon mitigation system fails to perform or exhibits unexpected behavior, use these diagnostic troubleshooting protocols to locate and resolve the issue.

Scenario A: The Manometer Fluid Level Remains Completely Level (Reading Zero)

• Root Cause: There is an absolute loss of suction, either due to a lack of electrical power to the fan, a failed fan motor capacitor, or a physical disconnection in the PVC piping between the manometer and the fan.
• Actionable Fix:
  
  
  1. Verify that the system's electrical circuit breaker is on and the attic/exterior disconnect switch is set to "ON".
  2. Inspect the flexible rubber couplings on the suction and exhaust sides of the fan to ensure they are tight and have not slipped off the PVC pipe.
  3. Ensure the vinyl tube running from the top of the U-tube manometer into the PVC pipe is not kinked, clogged with condensation, or disconnected from the pipe port.

Scenario B: Severe Condensation Noise or "Gurgling" in the Vent Pipe

• Root Cause: A portion of the horizontal run of PVC pipe is sagging or does not have the minimum required 1/8-inch per foot slope back toward the suction pit. This allows water condensation to pool in a low spot, restricting airflow and creating a loud gurgling sound.
• Actionable Fix:
  
  
  1. Use a digital level to inspect all horizontal runs of the PVC vent line.
  2. Re-adjust the pipe hanger straps to eliminate any sags and re-establish a continuous, downward slope back to the suction pit.
  3. If a joist or structural beam prevents proper sloping, route the pipe along an alternative path or install a dedicated condensate bypass loop.

Scenario C: Backdrafting of Natural Draft Combustion Appliances

• Root Cause: The high-suction radon fan is drawing air from the basement so aggressively that it has depressurized the utility room, causing carbon monoxide and combustion exhaust from a gas water heater or furnace to flow backward down their chimneys and enter the living space.
• Actionable Fix:
  
  
  1. Perform a combustion safety backdrafting test in the Combustion Appliance Zone (CAZ) with the radon fan running.
  2. Seal any unsealed sump pump pits, expansion joints, or large slab cracks to prevent the system from pulling conditioned indoor air from the basement.
  3. If depressurization continues, install combustion makeup air ducts to supply fresh outdoor air directly to the utility room, or replace the natural draft appliances with direct-vent, sealed-combustion units.

Frequently Asked Questions

Can I use thin-walled Schedule 30 PVC or flexible ducting for radon piping?

No. Standard residential building codes and radon mitigation standards (specifically ANSI/AARST) prohibit the use of flexible ducting or thin-walled Schedule 30 PVC. You must use Schedule 40 PVC, which is thick enough to resist physical impacts, support long vertical runs, prevent air leakage, and suppress the operational airflow noise generated by the fan.

Where should the inline radon fan be physically located?

The radon fan must be located outside the conditioned envelope of the home. Acceptable locations include an unconditioned attic, an unconditioned garage attic space, or mounted on an exterior wall of the home. It must never be installed in a basement, crawlspace, or occupied room, as any leak on the pressurized discharge side of the fan would pump raw radon gas into the living space.

How long after installation should I perform a clearance test?

You must wait a minimum of 24 hours after activating the radon system before starting a post-mitigation radon clearance test. This delay allows the fan to establish a stable sub-slab vacuum field and exhaust any radon gas that was previously trapped within the home's air volume. Run a 48-hour to 72-hour test to verify the system has brought radon levels below the EPA action limit of 4.0 pCi/L.

How much electricity does a radon mitigation fan consume?

Most standard residential radon mitigation fans are highly efficient, drawing between 40 and 150 watts of continuous power depending on the model and the static pressure of the soil. This equates to approximately $50 to $150 per year in electrical operating costs, depending on your local utility rates.

Take Action to Protect Your Indoor Air Quality

Ensure your radon mitigation project meets the highest levels of safety and scientific precision by closely monitoring post-mitigation pressure fields. If you find your sub-slab conditions require complex diagnostic testing or advanced multi-point suction engineering, consult a certified NRPP or AARST professional to guarantee long-term safety for your home.