Radon sneaks into houses quietly, without odor or color to warn you. I have tested hundreds of homes across the Midwest, including plenty in St. Louis City and County, and I can say with confidence that you cannot guess your radon risk by age of the house, neighborhood, or even whether a neighbor’s test came back clean. Homes that look identical on the same block often produce very different readings. The only honest starting point is a measurement. From there, you decide whether a radon mitigation system makes sense and, if so, how quickly to move.
Below, I lay out the clearest signs you need a system, what those signs look like in real houses, and the practical details that help you choose a path forward without wasting time or money. The focus is on plain facts, numbers you can act on, and what I have seen in the field.
What radon is doing in your house, even if you can’t see it
Radon forms naturally when uranium in soil and rock breaks down. The gas seeps upward and uses the path of least resistance into your home. Foundation cracks, sump pits, utility penetrations, gaps around plumbing, and even porous block walls all act like open doors. Your heating and cooling system can create a slight negative pressure inside, which draws soil gases in faster. When that gas builds up indoors, you breathe it. Over months and years, radon’s radioactive decay products lodge in the lungs and raise the risk of lung cancer. The Environmental Protection Agency recommends mitigation at or above 4.0 picocuries per liter, often written as 4.0 pCi/L. Many health agencies also encourage action between 2.0 and 3.9 pCi/L. That range recognizes a simple truth: lower is safer.
In older St. Louis basements, especially those with limestone or brick foundations and exposed aggregate floors, I frequently see radon concentrate during cold months. Homes with tight, energy-efficient envelopes can also trap more radon because the natural air exchange is low. On the flip side, drafty houses sometimes show seasonal dips, yet still spike when windows close or when the furnace cycles more often. The pattern varies, but the mechanism stays the same. Soil, entry paths, indoor pressure, and ventilation.
The top signs you need a mitigation system, explained with real-world context
The strongest sign is a verified test result above guideline levels. Still, there are other indicators that tell you to test again, dig deeper, or plan a system now rather than later.
1) A radon test at or above 4.0 pCi/L
This is the bright line. If your measurement is 4.0 or higher, the EPA recommends installing a radon mitigation system. I have seen houses in Chesterfield and Kirkwood go from 8 to under 1 with a properly sized fan and a sealed sump lid. A straightforward active sub-slab depressurization system usually achieves 50 to 90 percent reduction, sometimes more. The timeline can be short. A qualified radon mitigation contractor can typically install within a day, then verify the results with a post-mitigation test.
2) Repeated readings between 2.0 and 3.9 pCi/L, or winter spikes that cross 4.0
Many families get a 2.8 in spring and feel relieved. Then January hits, the basement turns into the TV room, and a follow-up test lands at 4.6. If you spend significant time in lower levels, particularly if you sleep in a basement bedroom, levels near 3.0 are a signal to act. I often advise clients in the 2 to 4 range to consider their exposure, the age and health of occupants, and how often they open windows. If the basement is finished space, an active system is a reasonable investment, and it usually lifts home value at resale. Buyers are increasingly familiar with radon in the St. Louis market. Seeing a neat exterior stack, labeled radon fan, and a manometer inside the basement reads like a safety upgrade, not a defect.
3) A neighbor’s high result combined with your home’s geology and foundation type
Radon varies lot by lot, so a neighbor’s 10.0 does not automatically mean yours is high, but it raises the odds. The St. Louis region sits on mixed soil profiles, with areas of karst and fractured limestone that can channel soil gas efficiently. If your foundation is a slab-on-grade or you have a crawl space with bare earth, the risk of elevated levels increases. In subdivisions where testing is common, I have watched one side of a street average 6 to 12 pCi/L while the opposite side averaged under 3. The difference traced to subtle grade changes and how stormwater drained. When a neighbor flags a problem, test promptly and be prepared to install if your result confirms it.
4) Unsealed or partially sealed sump pit, significant floor cracks, or hollow-block walls
If I walk into a basement and see a wide crack running the length of the slab, an open sump pit with a pump sitting on bare gravel, or hollow block walls that vent into the basement air, I expect higher readings. I have mitigated houses where sealing the sump lid alone dropped the level by one or two points, though sealing by itself rarely solves the entire problem. The more open pathways the soil gas has, the greater the draw into your interior. A radon system turns that flow around by creating a pressure field under the slab, pulling gas into a pipe, and venting it above the roofline.
5) Kids, older adults, or anyone who spends long hours in basement rooms
Health risk scales with dose over time. If the basement is a playroom, home office, or a bedroom, and you log hundreds of hours down there each season, even mid-range readings justify action. I often tell clients who work from home in a lower-level office to assume they live in that environment eight hours a day. A 3.5 with minimal time downstairs is one thing. A 3.5 with daily occupancy is another. The cost of a well-installed Radon mitigation system is typically lower than many remodeling projects and pays back in peace of mind.
Short-term tests, long-term monitors, and the numbers that matter
Not all tests are created equal. The standard short-term kit runs 48 to 96 hours. It gives a quick decision point for real estate transactions or initial screening. Follow the instructions carefully: close windows at least 12 hours before starting, place the device 20 inches to 6 feet above the floor, stay away from drafts and exterior walls, and position it in the lowest livable level.
For homeowners who want a better picture of seasonal swings, a 90-day to 12-month test levels out weather and gives a truer average. In homes around St. Louis, I often see a winter-to-summer swing of 1 to 3 pCi/L, sometimes larger in very tight or very open houses. Continuous radon monitors, available for purchase, can help you see trends, especially if you plan to finish a basement or change ventilation habits. Watch for weekly patterns as well. I have observed Monday spikes in houses where laundry days and bathroom exhausts ran longer, subtly increasing negative pressure.
If a short-term test comes back near the action level, run a follow-up either as a second short-term test under closed-house conditions or, better, a longer test that includes colder weather. Most buyers and many lenders accept a certified active monitor test after mitigation to verify the fix worked.
What a mitigation system does and what a good installation looks like
A modern Radon system is simple in principle. A contractor cores a hole in the slab, digs a small pit to lower soil resistance, then runs PVC pipe from the slab area to an inline radon fan that vents outdoors above the roofline. The fan creates a slight vacuum under the slab, intercepting soil gas before it enters the house. Sealing cracks and the sump lid improves the system’s efficiency because the fan pulls more from the soil and less from your interior air.
Inside a well-executed job, you will see clean PVC runs, solvent-welded joints, a proper electrical disconnect, a labeled radon fan rated for outdoor use, and a U-tube manometer mounted on the interior pipe. That manometer shows a pressure differential when the fan runs. If both fluid levels are even, the fan is off or failed. I advise homeowners to glance at the manometer whenever they are in the basement. It is the simplest health check for your system.
Sizing matters. A basement with thick gravel under the slab often needs a smaller fan than a compacted-clay site. Large homes with multiple slab sections or thick structural slabs sometimes require two suction points or a higher capacity fan to achieve uniform sub-slab pressure. Block-wall depressurization, crawl-space membranes with dedicated suction, or drain tile integration all belong in the toolkit of a capable radon mitigation contractor. If a contractor insists on a one-size-fits-all approach without asking about drainage tile or slab thickness, get a second quote.
St. Louis nuances: why local experience helps
Radon around St. Louis is neither the worst in the country nor trivial. The variability is what catches people off guard. I have mitigated post-war ranches in Affton that hit the teens, and rehabbed two-story homes in the city that tested under 2. In parts of West County, where crawl spaces meet slabs and walk-out basements complicate air movement, I often design hybrid systems. Brick veneer with open weep holes can also create odd pathways, where negative pressure in wall cavities pulls more soil gas. None of this is guesswork once you test, but these patterns explain why Stl radon results run the gamut.
When clients search Radon mitigation St Louis or Radon mitigation near me, they usually find a mix of national firms and local specialists. There is value in both. The key is to ask about regional experience: block-wall issues in older city housing stock, sump lids in homes with interior drain tile, and code requirements for exterior vent terminations. Local pros know how winter stack effect in our climate shifts readings, and they size systems with that in mind.
What it costs and how to think about value
Most standard installations in the region fall in the 1,100 to 1,800 dollar range, sometimes more if the home needs multiple suction points, a long exterior run, or crawl-space encapsulation. Exterior aesthetics can add to cost if you route pipe through a garage to hide it. I advise clients to weigh three things:
- Expected reduction and verification: You should receive a post-mitigation test showing results, typically within a week or two of running the system continuously. System noise and placement: Fans are quiet, but you do not want one mounted where bedroom windows pick up the hum. A competent installer will propose locations that balance performance and comfort. Long-term reliability and serviceability: The fan is the only moving part. Typical lifespan runs 5 to 10 years, depending on fan model and load. Replacement cost is modest compared to the original installation.
A well-executed Radon mitigation system also smooths real estate transactions. Buyers ask about radon more than they did ten years ago. Seeing a documented system, clear labels, and a low post-test can keep a deal on track.
Edge cases and trade-offs that matter
I occasionally meet homeowners who rely on ventilation alone, opening basement windows much of the year. On mild days, ventilation can lower levels, but it is weather dependent and unreliable in winter and summer. If your reading is clearly high, fresh air alone is not an adequate plan.
Another edge case is a house with under-slab ductwork for a forced-air system. Those ducts can collect radon and distribute it. The design of a mitigation system needs to consider duct sealing and sometimes a different suction point to avoid drawing household air into the ducts. In a few older St. Louis homes, I have also seen drain-tile systems tied directly into a sanitary line. That requires care to avoid pulling sewer gas into the system.
There are rare scenarios where a home’s architecture makes standard routing very difficult. In those cases, interior pipe runs hidden within closets, with a roof penetration through the attic, can preserve curb appeal while maintaining system performance. Professional judgment shows up in these decisions, balancing function, aesthetics, and code.
How to choose a contractor without second-guessing
Look for certification from recognized bodies and ask for recent local references. A good Radon mitigation contractor will walk the property, check slab conditions, look for drain tile, test suction points during installation, and show you the operating manometer before leaving. You should receive a clear diagram of the system, labeling on the pipes, and written guidance on fan operation and what to do if the manometer reads zero.
Pricing should be transparent. If the quote skips post-mitigation testing or ignores potential complications like a crawl space, expect change orders later. In my experience, two or three competitive quotes give you a fair view of market pricing for St louis radon work and reveal who is treating your home as a one-off design versus a template job.
Maintenance, monitoring, and the quiet routine that keeps levels low
After installation, your job is simple. Keep the fan powered. Check the manometer now and then. If your home has a sealed sump lid, make sure anyone servicing the pump re-seals the lid properly. If you remodel, especially if you cut new slab openings or alter mechanical systems, run a follow-up radon test. Fans do wear out with time. Many homeowners swap a fan every 7 to 10 years. Replacement takes an hour or two.
Seasonal checks pay off. I suggest a short-term test every couple of years, and sooner if you notice changes in basement humidity, new cracks, or long periods with windows closed. Continuous consumer monitors have improved in reliability and price. Place them where you spend time, not in dead corners. Watch for persistent rises rather than day-to-day wiggles.
Selling or buying a home with radon on the table
If you are selling and your pre-listing test reads high, install a system now. It takes a negotiating chip off the buyer’s list and avoids a rush-job during escrow. If you are buying and a test pops above 4.0, you can ask for mitigation or a credit. In both cases, require a post-mitigation test with a properly calibrated device. I have walked buyers through houses where a system ran but the manometer was flat, fan unplugged. The fix was simple, but the verification step matters.
For new construction, many local builders install airsenseenvironmental.com St louis radon passive systems, sometimes labeled as a Radon system in the listing. These help, especially when the rough-in includes a good sub-slab gravel layer and a dedicated vent path. In higher-radon pockets, activating the passive system with a fan can be the difference between a 3.5 and a 0.7. If you see a passive stack, ask for a test before and after activation.
When the numbers refuse to drop and what to do next
In a small fraction of homes, the first attempt does not achieve the target. The usual culprits are poor communication under the slab, a missed entry pathway like a dirt crawl, or an undersized fan. A methodical approach works:
- Smoke sticks or pressure field extension tests around cracks and utility penetrations to see if the vacuum reaches problem areas. Sealing the sump lid properly and gasketing any removable sections, with clear view panels for maintenance. Adding a second suction point or switching to a higher capacity fan if soil resistance is high.
In my practice, the second pass succeeds the vast majority of the time. It is rare to need three or more iterations, and when that happens, complex geometry or mixed foundations are usually to blame. A patient contractor with the right instruments can untangle even stubborn layouts.
A quick self-check to decide your next step
- You have any test at or above 4.0 pCi/L, or repeated results in the 2.0 to 3.9 range with regular basement use. Your basement has an open sump, visible slab cracks, or hollow-block walls that breathe into living space. A nearby home reported high results and your foundation type or soil suggests easy gas movement. You plan to finish the basement or add a bedroom below grade and want a healthy baseline. You value smoother resale and fewer surprises during buyer inspections.
If any of these fit, schedule a professional test if you have not already, then consult a qualified Radon mitigation contractor for a design and quote. If you prefer to start with a DIY short-term test, you can pick one up at a hardware store or order a certified kit online. Just remember to follow placement and closed-house rules, and to confirm high or borderline results with a second test.
Final thought from years in basements and crawl spaces
Radon is not a problem to fear, it is a problem to measure and manage. A well-designed Radon mitigation system is one of the most effective environmental fixes you can make to a home. It is quiet, it runs in the background, and it gives you hard numbers that show the benefit. Whether you searched Stl radon after a neighbor’s scare or typed Radon mitigation near me because a buyer’s inspector flagged an issue, the path is the same. Test carefully, read the results with context, and work with a pro who treats your house like a one-off. That is how you turn an invisible risk into a well-controlled variable.
Air Sense Environmental – Radon Mitigation & Testing
Business Name: Air Sense Environmental – Radon Mitigation & TestingAddress: 5237 Old Alton Edwardsville Rd, Edwardsville, IL 62025, United States
Phone: (618) 556-4774
Website: https://www.airsenseenvironmental.com/
Hours:
Monday: 9:00 AM – 5:00 PM
Tuesday: 9:00 AM – 5:00 PM
Wednesday: 9:00 AM – 5:00 PM
Thursday: 9:00 AM – 5:00 PM
Friday: 9:00 AM – 5:00 PM
Saturday: Closed
Sunday: Closed
Plus Code: RXMJ+98 Edwardsville, Illinois
Google Maps URL: https://maps.app.goo.gl/XTPhHjJpogDFN9va8
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https://www.airsenseenvironmental.com/Air Sense Environmental is a local indoor air quality specialist serving Edwardsville, IL and the surrounding Metro East region.
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Popular Questions About Air Sense Environmental – Radon Mitigation & Testing
What services does Air Sense Environmental provide?
Air Sense Environmental provides professional radon testing, radon mitigation system installation, indoor air quality solutions, and crawl space encapsulation services in Edwardsville, Illinois and surrounding areas.Why is radon testing important in Illinois homes?
Radon is an odorless and invisible radioactive gas that can accumulate indoors. Testing is the only way to determine radon levels and protect your household from long-term exposure risks.How long does a professional radon test take?
Professional radon testing typically runs for a minimum of 48 hours using continuous monitoring equipment to ensure accurate results.What is a radon mitigation system?
A radon mitigation system is a professionally installed ventilation system that reduces indoor radon levels by safely venting the gas outside the home.How do I contact Air Sense Environmental?
You can call (618) 556-4774, visit https://www.airsenseenvironmental.com/, or view directions at https://maps.app.goo.gl/XTPhHjJpogDFN9va8 to schedule service.Landmarks Near Edwardsville, IL
Southern Illinois University Edwardsville (SIUE)A major public university campus that serves as a cultural and educational hub for the Edwardsville community.
The Wildey Theatre
A historic downtown venue hosting concerts, films, and live entertainment throughout the year.
Watershed Nature Center
A scenic preserve offering walking trails, environmental education, and family-friendly outdoor experiences.
Edwardsville City Park
A popular local park featuring walking paths, sports facilities, and community events.
Madison County Transit Trails
An extensive regional trail system ideal for biking and walking across the Metro East area.
If you live near these Edwardsville landmarks and need professional radon testing or mitigation, contact Air Sense Environmental at (618) 556-4774 or visit https://www.airsenseenvironmental.com/.