If you have discovered elevated radon levels in your home, you have probably wondered how these mitigation systems actually work. The good news is that the underlying principle is straightforward, and the technology has been refined over decades to achieve remarkable effectiveness.
This guide breaks down the science and engineering behind radon mitigation. You will understand why these systems work so well, what components make up a complete system, and what to expect during and after installation.
Key Points About Radon Mitigation
- Simple principle: Create negative pressure to draw radon away before it enters
- Proven technology: Same basic design used successfully since the 1980s
- Quick installation: Most systems installed in a single day
- Low maintenance: Systems require minimal attention once installed
1. The Core Principle: Pressure Differential
Radon enters your home because of pressure differences. The air pressure inside your home, especially at lower levels, is typically slightly lower than the pressure in the soil beneath your foundation. This creates a gentle suction effect that draws soil gases, including radon, into your living space.
Radon mitigation systems work by reversing this pressure relationship. By creating even lower pressure beneath your foundation than inside your home, the system ensures that soil gases flow away from your living space rather than into it.
How Pressure Differential Works
Without Mitigation:
- • Home interior: Lower pressure
- • Soil beneath foundation: Higher pressure
- • Result: Radon flows INTO home
With Mitigation:
- • Home interior: Normal pressure
- • Sub-slab area: Lower pressure (from fan)
- • Result: Radon flows AWAY from home
The beauty of this approach is that you do not need to seal every crack or opening in your foundation. As long as the sub-slab pressure is lower than the interior pressure, radon will naturally flow toward the mitigation system rather than into your home. The system essentially creates a path of least resistance that directs radon safely outdoors.
2. Types of Radon Mitigation Systems
Several types of radon mitigation systems exist, each suited to different home configurations. The most common and effective type is Active Soil Depressurization (ASD), but the best choice depends on your home's construction.
Sub-Slab Depressurization (SSD)
The most common type. A pipe is inserted through the concrete slab into the gravel or soil below. A fan creates suction to draw radon from beneath the slab.
Best for: Homes with basement or slab-on-grade foundation
Sub-Membrane Depressurization (SMD)
Used for dirt-floor crawl spaces. A heavy plastic membrane covers the soil, and a pipe with fan draws radon from beneath the membrane.
Best for: Homes with crawl spaces
Block Wall Suction
For homes with hollow block foundation walls. Suction is applied to the interior of the block walls to draw radon before it enters.
Best for: Homes with hollow concrete block foundations
Heat Recovery Ventilator (HRV)
Increases ventilation to dilute radon. Less effective than ASD but can be used in combination or where ASD is not feasible.
Best for: Supplemental reduction or unusual situations
For most homes in the Atlanta area and throughout the Southeast, sub-slab depressurization is the standard approach. It offers the best combination of effectiveness, reliability, and cost-efficiency.
3. System Components Explained
A standard radon mitigation system includes several key components, each serving a specific function. Understanding these parts helps you maintain your system and recognize if something needs attention.
1Suction Point
A 4-5 inch hole drilled through the slab into the gravel or soil below. This is where the system draws radon from beneath your home. Some homes need multiple suction points for full coverage.
2PVC Piping
Schedule 40 PVC pipe (typically 3-4 inches diameter) connects the suction point to the fan and extends to the discharge point. White PVC is standard, though it can be painted to match your home.
3Radon Fan
The heart of the system. Specialized fans designed for continuous operation create the suction that draws radon away. Installed in the attic, garage, or exterior of the home, never in living spaces.
4Discharge Point
The pipe extends above the roofline or to an exterior location away from windows. Radon disperses rapidly into outdoor air, where it poses no health risk.
5Manometer
A simple U-tube gauge that shows the system is creating suction. When the liquid levels are uneven, your system is working. A critical visual indicator of system operation.
6Electrical Connection
The fan requires a dedicated electrical circuit. Professional installations ensure proper electrical connections that meet code requirements.
4. The Installation Process
Professional radon mitigation installation typically takes 3-5 hours for a standard residential system. Here is what to expect:
Site Assessment
The technician evaluates your home, identifies the best location for the suction point, plans the pipe routing, and determines fan placement. This happens before or at the start of installation.
Core Drilling
A 4-5 inch hole is drilled through the concrete slab. The technician removes some material from beneath to create a suction pit. This is the loudest part of the installation.
Pipe Installation
PVC piping is connected to the suction point and routed to the fan location. Depending on your home, pipes may run through closets, garages, or along exterior walls.
Fan Installation
The radon fan is installed in the attic, garage, or exterior location. The fan is connected to the piping above and below, and electrical connections are made.
Discharge and Sealing
The discharge pipe extends above the roofline or to an appropriate exterior location. All penetrations are sealed, and the manometer is installed.
System Activation and Testing
The fan is turned on, and the technician verifies proper operation. A post-mitigation radon test is scheduled to confirm the system has reduced levels adequately.
5. How Effective Is Mitigation?
Radon mitigation is remarkably effective. Professional systems consistently achieve 95-99% reduction in radon levels. The EPA states that properly installed active soil depressurization systems can reduce radon to below 2 pCi/L in virtually all homes.
Real-World Results
That is a 93% reduction, and many systems achieve even better results.
The system begins working immediately upon activation. Within 24 hours, most of the radon reduction has occurred. Post-mitigation testing is typically performed 24-48 hours after installation to verify results.
In rare cases where initial results are not adequate, adjustments can be made. Additional suction points, a more powerful fan, or sealing of major foundation cracks can improve performance. Experienced contractors know how to diagnose and address these situations.
See It in Action: This Old House Explains Radon Mitigation
Watch the experts at This Old House explain how radon testing and mitigation systems work to protect your home.
Video courtesy of This Old House
6. Understanding Costs
Radon mitigation is one of the more affordable home safety investments you can make. Understanding what affects cost helps you evaluate quotes and make informed decisions.
Typical Cost Ranges
Factors That Affect Cost
- Foundation type: Slab foundations are typically simpler than basements with multiple foundation sections
- Home size: Larger homes may need multiple suction points
- Pipe routing: Interior routing is typically less expensive than exterior
- Accessibility: Difficult access adds time and cost
Ongoing Costs
Operating costs are minimal. The fan runs continuously but uses only about as much electricity as a 75-watt light bulb. Most homeowners see an increase of $3-$8 per month on their electric bill, or roughly $50-$100 per year.
7. Maintenance Requirements
One of the best things about radon mitigation systems is how little maintenance they require. Once properly installed, these systems run reliably for years with minimal attention.
Monthly Check (30 seconds)
- • Glance at manometer to verify system is running
- • Liquid should show uneven levels
- • Listen for normal fan operation if accessible
Every 2 Years
- • Retest radon levels to confirm continued effectiveness
- • Professional testing recommended
- • Test after any major home renovations
Signs Your System Needs Attention
- Manometer shows equal levels (no suction)
- Unusual fan noise (grinding, rattling, or silence)
- Retest shows elevated radon levels
Radon fans typically last 10-15 years before needing replacement. Fan replacement is straightforward and costs $300-$600 including installation. The PVC piping and other structural components last 25+ years or the lifetime of the home.
8. Choosing a Qualified Contractor
The effectiveness of your mitigation system depends heavily on proper installation. Choosing a qualified, experienced contractor ensures you get a system that works correctly from day one.
What to Look For
- Certification: Look for NRPP (National Radon Proficiency Program) or NRSB (National Radon Safety Board) certification
- Experience: Ask how many systems they have installed and their success rate
- Insurance: Verify they carry liability insurance
- Warranty: Reputable contractors guarantee their work
- Post-mitigation testing: They should include or recommend testing to verify results
Be cautious of unusually low bids. Proper mitigation requires quality materials and experienced installation. A system that does not work properly is not a bargain at any price.
9. Frequently Asked Questions
10. Get Started with Mitigation
If your home has elevated radon levels, mitigation provides a proven, permanent solution. Most homeowners are surprised at how straightforward and affordable the process is.
