Walk into enough basements and you begin to smell patterns. Damp limestone foundations in older brick homes, tight new construction with sprayed foam, crawlspaces breathing into floor cavities. Every building teaches you something about air, pressure, and the hidden paths gas will take if you let it. Radon behaves like a polite trespasser: it does not force doors, it waits for us to create a pressure difference, a crack, a sump, and it slips in. Understanding radon mitigation is mostly understanding physics in slow motion, plus some geology and hard-earned judgment about how houses actually move air.
This is a deep look at how a radon system works, what the data says about performance, where things go wrong, and how a smart installation adapts to soil, structure, and season. If you are deciding whether to call a radon mitigation contractor, or if you already have a fan humming on your foundation wall and want to know what it’s really doing, the science helps you make better choices.
What radon is and why houses collect it
Radon is a radioactive gas that seeps from soil when uranium decays in rock and dirt. It has no color, smell, or taste, which makes testing non-negotiable. Outdoors, it dilutes quickly and rarely matters. Indoors, we create the perfect trap. As warm air rises and leaves through the top of a building, the stack effect pulls replacement air from the lowest level. If the path of least resistance is through cracks, joints, a drain tile system, or a dirt crawlspace, we pull soil gas along with that make-up air. Concrete looks solid but it leaks at the slab-to-wall seam, at control joints, and through hairline shrinkage fractures that the eye ignores but pressure does not.
The Environmental Protection Agency sets an action level at 4.0 pCi/L. Plenty of homes in the upper Midwest and along ancient river valleys test higher than that, especially in winter when windows close and the stack effect strengthens. In the St. Louis area, I have personally logged homes that swing from 2.5 pCi/L in May to 10 to 20 pCi/L in January, with the same slab and the same fan off. That kind of variance is why any serious conversation about St Louis radon starts with seasonal data, not a single number.
The core idea: sub-slab depressurization
A Radon system does not “filter” radon. It changes pressure. The standard approach, called active sub-slab depressurization (ASD), uses a fan to create a slight vacuum under the slab or membrane so that soil gas flows to a controlled discharge point outdoors rather than into the living space.
You drill or core through the slab, dig a small pit into the aggregate, and connect PVC piping from that suction point to a fan mounted outside or in the attic or garage. The fan pulls soil gas from under the slab, routes it up and away, and exhausts it above the roofline. If the sub-slab material is coarse gravel that communicates well, one suction point often serves a large footprint. If the sub-slab is tight clay or poorly compacted fill, you may need additional points or a completely different strategy like sub-membrane depressurization in a crawlspace.
The physics is simple: gas follows pressure gradients. Lower pressure under the slab relative to the basement air reverses the natural flow into the home. We aim for a pressure field extension that reaches under the entire slab. You do not need a large vacuum, only enough to move gas freely. Most residential radon fans create between 0.5 and 4 inches of water column in the pipe and move 50 to 150 cubic feet per minute depending on resistance. The exact numbers do not matter as much as the result measured in the home’s air.
Why fans matter more than seals
Homeowners often ask if they can just seal the cracks. Sealing helps, but not to the degree people hope. Concrete shrinks and moves, and you will never find every capillary path a gas can use over time. Sealing buys efficiency, not victory. The fan does the heavy lifting by capturing gas before it reaches the slab. In my notes from hundreds of mitigations, sealing alone rarely cuts levels by more than 10 to 20 percent. Add a properly sized fan and a good suction field, and reductions of 70 to 95 percent are common.
There is still an art to sealing. You always address large visible openings: an open sump lid, a utility penetration, gaps where the slab meets the wall. Seal those, and the system wastes less energy pulling conditioned air from the basement or crawlspace rather than soil gas. A clear, tight sump cover with gaskets and ports for pump lines is not optional. It is the kind of detail that separates a Radon mitigation system that hums along for years from one that rides the edge of acceptable and drifts higher every winter.
Pressure field extension, or how far your suction reaches
You can think of the sub-slab area as a shallow, leaky plenum. The goal is to make that plenum slightly negative relative to the interior. Where installers often go wrong is assuming one suction point always suffices. In a ranch with a single slab pour over clean gravel, one point through the mechanical room often does. In a split-level with grade beams, footings, or multiple pours separated by interior foundations, the vacuum may die at the first barrier.
The practical way to confirm is a smoke test or pilot holes with micro-manometers. Drill small test holes in far corners, drop in a probe, and read the pressure change when the fan runs. If those far points show a consistent negative pressure under the slab, the system is set. If they do not, you add suction points or change the fan. I have seen houses where a second point at the other end of the basement dropped long-term levels by half, even though the first point already looked “good” on paper. Real houses, with clay pockets and compacted silt, do not always match drawings.
Pipe size, routing, and the quiet war against friction
Friction steals fan performance. Every elbow and every foot of pipe adds resistance. Two design rules hold up well:
- Keep runs as short and straight as the layout allows. Choose pipe diameter to balance velocity and loss, commonly 3 inch for most residential jobs and 4 inch when long vertical runs or multiple points demand lower friction.
Horizontal piping below the slab is rare in retrofits, but above-slab routing matters. A gentle sweep elbow flows better than a hard 90 degree. Multiple 90s in quick succession can force a smaller fan to its high-pressure, low-flow corner, right where you do not want to operate. When planning a Radon mitigation near me search, ask the contractor how they size the fan and pipe. If the answer is “we always use X,” be cautious. Good contractors adapt.
Fans by the numbers, and why high suction is not always better
Fan models range from low-power units that whisper along at 50 watts to heavy-duty units that pull through tight sub-slab soils at 150 watts or more. Bigger fans can overcome resistance, but they also move more heated or cooled air from the building if the slab leaks or the sump is not sealed. That can increase energy bills and, counterintuitively, pull more radon into the house from areas outside the pressure field if the system is poorly detailed.
In most houses with a decent gravel bed, a mid-range fan handles the load. In very tight clay, you either work to improve communication by coring a larger suction pit, or you add an extra suction point with a moderate fan rather than jumping to the most aggressive model. The choice affects noise, energy use, and long-term reliability. I have swapped out “muscle fans” that masked design flaws with brute force and replaced them with two moderate units serving separate zones. The readings stabilized and the owners saved on electricity.
Exhaust location and the myth of the magic roofline
The purpose of the discharge is to throw the exhaust away from openings where it can be drawn back in. Roofline terminations do this well because the plume disperses and stack effect pulls it upward. Sidewall discharges can work if they respect clearances from windows, soffit vents, and neighboring structures, but wind eddies and seasonal pressure differences can cause re-entrainment. I prefer roof terminations unless the architecture or local code dictates otherwise. In a tight neighborhood where houses sit close, a high vertical discharge matters more than people realize.
In winter, exhaust condensation can frost the outlet. That is normal. However, if you see heavy staining or water pooling in the pipe, the slope is wrong or the condensate drain strategy is missing. Water weight inside the piping saps performance and shortens fan life.
Measuring success: short-term spikes and long-term truth
You validate a Radon mitigation system with testing. A certified professional should retest 24 hours after activation with a short-term device to confirm immediate reduction. That number is a snapshot. The set of readings that matter more live in long-term data, 90 days or, better yet, a full heating season. Long-term monitors now cost little and give a moving average so you can see changes when the ground saturates after a storm or when high winds push pressure against one side of the house.
In the St. Louis region, clay soils swell and dry, river levels shift the water table, and older basements breathe differently week to week. A system that holds 0.9 to 1.5 pCi/L in October through March is doing its job. If you see a steady creep toward 3 to 4 pCi/L with the same fan and weather conditions, call your Radon mitigation contractor. Something changed, possibly a new crack, a loosened sump cover, or a fan entering its last months.
Crawlspaces, slabs, and the hybrid house problem
Plenty of homes pair a slab-on-grade section with a crawlspace or add a basement under an addition. Each zone may need its own approach. Sub-membrane depressurization in a crawlspace uses a durable plastic sheeting sealed to the walls and around piers, with a suction point under the membrane. In practice, the quality of that sealing decides the outcome. A loose sheet piles up at the perimeter and leaks like a sail. A properly sealed membrane with taped seams and mechanical attachment to the wall turns the entire crawl into a controlled plenum.
In split zones, a single fan can serve both a slab suction point and a crawlspace membrane if the piping paths and flows balance. More often, especially in homes with complicated footprints, two smaller fans serving two systems simplify control and make diagnostics easier.
New construction and passive systems that almost work
Building a passive radon rough-in into new construction costs little and pays back for the life of the home. The idea is the same: lay a layer of clean aggregate or a soil gas mat under the slab, connect a 3 or 4 inch pipe to a tee in that layer, run the pipe through the structure, and terminate it above the roof. You seal the slab edges and any penetrations. If the home’s natural stack effect is gentle and the sub-slab communicates well, a passive stack sometimes keeps levels below 4 pCi/L. In tighter homes or in higher emission areas, that passive stack acts as a ready-made pathway. You add a fan on the exterior where the stack rises and turn a maybe into a yes.
In practice, the “almost” is common. I have activated many passive stacks in newer subdivisions around St. Louis with a compact fan and watched 6 to 8 pCi/L readings fall below 1.5 pCi/L within a day. The existence of the stack saved time and avoided interior disruption.
Homes without slabs: drain tiles and sump systems
In many Midwestern homes, perforated drain tile runs along the footing, connecting to a sump pit. If the drain tile is continuous and open to the sub-slab aggregate, tapping the sump cover for suction often gives excellent results. The fan pulls through the tile and communicates along the foundation perimeter. When the tile is intermittent, clogged, or entirely absent, a direct sub-slab suction point is safer.
One caution in homes where the sump discharges to an interior drain or where the laundry or floor drains connect to old, partially open piping: make sure the system does not draw sewer gas. Proper traps, sealed lids, and attention to piping details prevent that problem.
Seasonal forces and the moving target
Radon entry is not a flat line. Consider a January storm in St. Louis with a deep low-pressure system. Indoor-outdoor pressure differences jump. The ground freezes at the surface, which caps diffusion and forces soil gas to follow paths under the frost line toward your foundation. Heavy rains fill pore spaces with water, changing gas flow patterns and sometimes pushing more into a basement. Wind stacks on the windward side and depressurizes the leeward side, changing where the house pulls air. An effective system accommodates these swings by maintaining a steady sub-slab vacuum across the year.
You see this in the data. Homes that sit at 1.2 pCi/L most of the year may bump to 2.2 pCi/L for a few days after a thaw, then slide back. That is entirely acceptable. What you do not want is a system that cannot keep up in the worst weeks, or one that only performs on mild days. That is another reason a reputable Radon mitigation contractor will size and test for the heating season even if they install in June.
Noise, aesthetics, and living with the system
Most fans are quiet enough that you forget them, especially if mounted on an exterior wall with vibration isolators. If you hear a rattle indoors, check for pipe contact with framing. If you hear a new whine after a few years, the bearings may be going. Typical residential fans last 5 to 10 years. A manometer on the pipe tells you at a glance whether the fan is pulling. The colored fluid should show a difference between the two columns. If it equalizes, the fan is off or has failed.
Aesthetics matter, especially at the front of a home. I route piping at the back corner where possible, paint exterior pipe to match the siding, and avoid odd diagonals. For brick fronts, a painted downspout cover or a chase can hide vertical runs. Small efforts like these make adoption easier for homeowners who plan to stay.
Energy use and indoor air side effects
A Radon mitigation system moves a modest amount of air from under the slab to the outdoors. If your slab is leaky to the interior, the makeup air may come from the basement. In cold climates, that can pull warm basement air out and increase heating demand slightly. You mitigate that by sealing obvious slab leaks and by avoiding oversizing the fan. In most houses I measure, the added energy cost lands around a few dollars a month. The health benefit is not hypothetical, so the trade-off is clear, but it is still smart design to keep operating costs low.
An ASD system does not depressurize the house itself when built well. If you notice persistent backdrafting at a water heater that was not present before, call the installer. You may have an interaction between the system and an atmospherically vented appliance. There are fixes, from additional sealing to upgraded combustion venting.
What separates a good install from a great one
Hiring matters. If you search Radon mitigation near me, you will find a range of providers. Strong work shows up in three places: diagnosis, detailing, and documentation. Diagnosis means testing, mapping the slab and any sub-slab utilities, and picking suction points that suit the house rather than the installer’s convenience. Detailing shows in sealed sumps, neat pipe runs, proper supports, labeled electrical disconnects, and a thoughtful discharge location. Documentation means a drawing or photo set, initial test results, fan model and serials, and clear instructions for the homeowner.
In St. Louis, local geology makes judgment important. Pockets of loess over clay, karst features in parts of the metro area, and a housing stock that mixes 100 year old basements with brand new slab-on-grade developments mean a one-size approach misses nuance. Reputable Stl radon professionals test before they bid, explain options, and do not promise miracles without caveats.
Edge cases: when systems struggle
Every so often, a house resists quick fixes. High water tables that flood the sub-slab aggregate can block air movement. A slab with radiant heat tubing complicates coring. Old stone foundations without a true slab create pathways that do not respect the usual rules. In those cases, hybrid strategies help. You may use both sub-slab and sub-membrane suction, add localized sealing at the wall-floor joint with backer rod and elastomeric sealant, or use a partial perimeter drain retrofit to create communication under the slab. I once worked a 1920s basement with a segmented floor that leaked at every panel edge. Two small fans on separate panels, plus sealing the visible seams and a tight sump cover, finally pulled the average down from 12 pCi/L to under 2 pCi/L across a winter. It took patience and pressure mapping to get there.
How long results last, and what maintenance looks like
Once dialed in, a Radon mitigation system is mostly hands-off. Homeowners check the manometer monthly and listen for changes in fan noise. If the fan dies, replacement is a one to two hour job. The sealants at the sump lid and major cracks hold up for years, though I re-bead obvious gaps when already on site for other work. After major structural changes, like finishing a basement, adding a bedroom over a crawlspace, or cutting in a new bath drain, test again. You may have changed pressure paths.
Radon levels in a region can drift over decades as groundwater patterns shift, but the larger variable is the house itself. If your long-term monitor begins to climb, even slowly, do not ignore Radon mitigation near me it. Most slips have a cause you can identify and fix.
What to expect when you call a pro
The first visit should include a review of prior test results, a look at the foundation, discussion of discharge options, and a written scope. A competent Radon mitigation contractor in the St. Louis area will quote a system that fits the home’s layout, not just the cheapest path to a pipe. Typical residential installs take half a day to a day. Drilling through the slab is loud for a short stretch. Dust control, cleanup, and patching distinguish careful crews from the rest.
After activation, plan on a follow-up test. I leave a continuous monitor for several days when possible and provide a printout. I also show the owner how to read the manometer and where the fan disconnect sits. A label on the pipe with the installer’s number and the fan model saves headaches later.
Common questions, answered clearly
- Will opening windows fix high radon? Temporarily, sometimes. It is not a solution. Seasonal comfort and security limit how often you can ventilate, and dilution is unpredictable. Can I vent the system into my attic or garage? No. That moves the problem. The exhaust must discharge outdoors where it can disperse safely. Do I need a bigger fan if my number is still 3.8 pCi/L? Maybe, but start with diagnostics. Another suction point or better sealing often solves what brute force cannot. Is radon only a winter issue? Levels often peak in winter, but I have measured summer spikes after heavy rains. Assume it is a year-round variable. How does a Radon mitigation st Louis project differ from other regions? Soil composition and housing age drive design choices. Around St. Louis, mixed foundations and clay content often demand extra attention to pressure field verification and sump detailing.
A brief checklist for homeowners before hiring
- Verify certification, insurance, and recent references in your area. Ask how they determine pressure field extension, not just where they plan to drill. Review discharge location and appearance, including painting or concealment options. Confirm follow-up testing and clear documentation will be provided. Discuss warranty terms for both workmanship and the fan.
The bottom line, grounded in physics and practice
A Radon mitigation system works because it persuades gas to choose an easier path than your basement air. It builds a small, reliable pressure difference where it counts, under the slab and membranes, then guides the flow outside where dilution makes it harmless. The success of that persuasion rests on soil communication, pipe routing and friction, fan selection, and a hundred small sealing decisions that add up to a steady vacuum.
If you live in the metro and type Radon mitigation near me or Radon mitigation St Louis into a browser, use the science to guide your questions. Ask how the installer will confirm the suction field, what they will do if the first point does not reach far corners, and why they chose a given fan. The good ones welcome those questions. They know that radon is not a mystery. It is a problem with clear physics, answered by careful work and verified by the numbers on a monitor that tell you your family is breathing easier.
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/This local radon mitigation and testing company is a reliable indoor air quality specialist serving Edwardsville, IL and the surrounding Metro East region.
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Homeowners throughout Edwardsville, IL rely on Air Sense Environmental for customer-focused radon reduction systems designed to safely lower elevated radon levels.
To schedule radon testing or mitigation service, call (618) 556-4774 or visit https://www.airsenseenvironmental.com/ to speak with a quality-driven local specialist.
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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/.