St Louis Radon: Testing and Mitigation for Safer Homes

Posted on 2026-02-21 21:21:17

Radon does not announce itself. It slips through the slab, rides up plumbing chases, and lingers in basements, crawlspaces, and lower-level living rooms without odor or color to betray it. In the St. Louis area, where limestone, clay soils, and a patchwork of older foundations meet variable weather, elevated radon shows up often enough that testing should be viewed as routine maintenance rather than an emergency measure. I have seen modest mid-century ranches in Webster Groves test at 1.8 pCi/L and similar homes just a few blocks away push 9 to 12 pCi/L. The difference was not craftsmanship or care. It was geology and pathways.

This guide draws on years of work in basements from Florissant to Festus, in gut rehabs in Benton Park, and in new builds in St. Charles. If you are searching for a Radon mitigation contractor or browsing Radon mitigation near me and seeing the same claims, you will find here the context to sort signal from noise. A good Radon mitigation system is not a commodity box; it is a set of choices, each adapted to your home and habits.

What radon is and why it concentrates in St. Louis homes

Radon is a radioactive gas produced by the natural breakdown of uranium in soil and rock. It moves up through the ground and into buildings through cracks and openings. Outdoors, it disperses quickly. Indoors, especially in colder months when windows are shut and stack effect draws air upward, it can accumulate to levels that increase lung cancer risk.

The Environmental Protection Agency sets 4.0 pCi/L as the action level, though many public health professionals prefer to mitigate down to 2.0 pCi/L or lower when feasible. I have tested homes in St. Louis City neighborhoods, suburban developments in Chesterfield, and post-war houses in Hazelwood. Roughly one out of three came back at or above 4.0 pCi/L. Some pockets, particularly in West County and the southern reaches of the metro where bedrock and soil composition vary, tend to produce higher readings. Missouri state data tracks with this: both sides of the river see enough elevated results that Radon mitigation St Louis should be a phrase as common as chimney cleaning or sump maintenance.

How testing works when done correctly

Testing is the first step, and it is messier than a single gadget on a coffee table would suggest. There are two main approaches: short-term and long-term testing. Short-term tests, using charcoal canisters or continuous radon monitors, run from 48 hours to a week. Long-term tests run for 90 days or more and capture seasonal swings.

A short-term test is ideal for a quick check or a real estate transaction. It is sensitive to weather, ventilation changes, and furnace or AC use. To make those results meaningful, maintain closed-house conditions for 12 hours before and during the test. That means windows shut, exterior doors used only for normal entry and exit, and no box fans pulling air to the outside. Place the device in the lowest livable area of the home, about 20 to 36 inches above the floor, away from drafts, high heat, or moisture sources. Do not set it in a kitchen or bathroom.

Long-term testing smooths out the noise. I encourage homeowners who get a short-term result around 3 to 5 pCi/L to follow with a long-term test to understand the annual average. I have seen May readings at 2.2 pCi/L climb to 6.8 pCi/L by January in the same home. That winter stack effect matters in St. Louis, where temperature swings are pronounced.

Professional testers use calibrated continuous radon monitors that log hourly data, which can be critical when a sale hangs on the outcome and both sides need assurance the test was conducted properly. Self-tests are fine for screening, but if you suspect tampering or the stakes are high, hire a professional or request a monitored test. The cost difference is small compared to the clarity you gain.

When to retest and how often

A single test is a snapshot. Retesting makes sense after any major foundation work, drainage changes, or HVAC modifications. New sump pits, a finished basement, or even extensive air sealing can change pressure dynamics. I recommend a retest every two to three years for peace of mind, and sooner if you remodel below grade. For homes with an active Radon system, test annually in the first couple of years, then every two to three years once performance is stable. Keep a written log of results, even if it is just dates and pCi/L numbers on a sheet taped near the Radon fan.

Understanding how mitigation actually reduces radon

Mitigation is about pressure and pathways. Radon enters where soil gas can slip in, then accumulates if the air is still. The common and reliable approach in this region is sub-slab depressurization. Think of it as a small vacuum under your slab that redirects soil gas to the outdoors before it can intrude.

A typical Radon system in St. Louis looks like this: a suction point is cored through the slab, aggregate or soil is removed to create a small plenum, and PVC piping carries gas up and out through an exterior wall or through the house to the roofline. An inline fan mounted outside living space, usually in the attic or on the exterior, pulls air from beneath the slab so the pressure there is slightly lower than the indoor pressure. That pressure differential is the heart of the system.

Success depends on four practical details. The suction point must reach a network of pathways under the slab. Older homes often have poor sub-slab communication because builders used compacted clay or the slab is segmented. A second or third suction point may be necessary. The fan must match the resistance under your slab, not just a default model in the contractor’s truck. The discharge should terminate above the eave and away from windows to prevent re-entrainment. Finally, the system must be sealed well, from the slab penetration to the PVC joints. Tiny leaks sap performance and invite condensation.

Crawlspaces and hybrid foundations require a different touch. In homes south of I-44, I often see a partial basement with an adjacent crawl. In those cases, sub-membrane depressurization over the crawlspace soil, tied into the same fan, is the cleanest approach. It involves laying a durable plastic membrane across the entire crawl floor, sealing to piers and walls, and connecting the membrane to the suction piping. Skipping that and trying to pull air through an unsealed crawl is a recipe for disappointment and dusty air.

Choosing a Radon mitigation contractor with local sense

When homeowners search Stl radon or St Louis radon and read a page of identical claims, they need a filter. Look for companies that probe before they propose. A site visit should include a pressure field extension test, notes on foundation types, slab thickness if known, sump conditions, and utility penetrations. If a contractor cannot describe how they will verify suction across the slab, or if they insist every house gets the same fan and a single suction point, keep looking.

I also weigh how they handle details that seem small but matter in daily life. Will they use a vibration isolation coupling where the piping meets the fan to limit hum on a quiet night? Do they plan to paint exterior piping to match siding rather than leave bright white PVC on a brick facade? Are they proposing a U-tube manometer and a label with system details near the fan? Small touches add up to pride of workmanship and fewer callbacks.

In St. Louis City, tight lot lines and historic facades push many installers to route to the rear. In some County municipalities, the discharge must be above the roofline. A seasoned contractor knows local codes and will place the Radon system with both performance and aesthetics in mind. Ask to see photos of similar homes they have treated in your neighborhood.

What a fair installation looks like, including costs

Prices vary with foundation complexity, the number of suction points, and aesthetic choices. In my experience across the metro, a straightforward single-suction sub-slab system in a typical 1,000 to 1,800 square foot footprint runs about 1,100 to 1,800 dollars. Add a sealed crawlspace with sub-membrane work and the range stretches to 2,000 to 3,500 dollars, sometimes more if access is tight or the crawl requires debris removal and grading. Multiple suction points or a garage-to-attic routed discharge can push a slab-only job into the 1,600 to 2,400 dollar band.

Permits and electrical outlets for the fan are line items. Some contractors prefer a licensed electrician to add a dedicated exterior-rated receptacle near the fan location. Others will hardwire in the attic when code allows. Ask how they plan to power the unit and ensure the solution is serviceable in the future.

The work itself typically takes four to eight hours. Expect some noise from coring, concrete dust control measures, and a clean patch at the suction point. A conscientious crew will aim the discharge to minimize visual impact and noise at windows. The fan hum is quiet, but not silent. On a still night, you can hear a gentle whir if you stand next to it. Proper mounting, vibration isolation, and a firm substrate keep that sound from telegraphing indoors.

After the fan goes on: verification and fine-tuning

A quality Radon mitigation system is only as good as its post-install test. Take a short-term test 24 hours after the fan runs continuously to allow the sub-slab pressure field to stabilize. Most professional installers place their own continuous monitor for a 48-hour check and include a lab-based confirmation test. Aim for well under 4.0 pCi/L. If your pre-mitigation level was 15 pCi/L, a post number around 1.5 to 2.5 pCi/L is a strong result. If you land at 3.5 pCi/L after a high baseline, discuss a second suction point or fan adjustment rather than stopping short.

I have had a few stubborn basements in South City with multiple floor levels and thick interior footings. In those cases, we added a second suction point on the far side of the footing and tied it into the same fan. Another common tweak is sealing a leaky sump lid and grommeting any penetrations. The fan does the heavy lifting, but sealing keeps the pressure where it belongs and improves energy efficiency by reducing conditioned air loss.

Operating costs, longevity, and what to expect over the years

Radon fans sip power. Most draw between 50 and 100 watts. At local electricity rates, that translates to roughly 45 to 110 dollars per year if they run 24/7, which they should. Fans last 7 to 12 years on average, sometimes longer if they are protected from weather and not forced to work against high resistance. When a fan fails, the first clue is the U-tube manometer reading equal on both sides or an audible change. Some systems include a small buzzer or light to indicate failure. Swapping a fan is a one to two hour job.

Keep the system simple to maintain. A clear-lidded sump cover with gaskets and pass-throughs you can open and reseal helps when the pump needs service. Labels and a dated installation sticker near the fan make home sales easier. Save all testing documentation in a dedicated folder. Buyers appreciate a paper trail, and frankly, so do appraisers who may not be radon experts.

Special cases: finished basements, additions, and new construction

Finished basements pose a trade-off between aesthetics and performance. If the ideal suction point falls under a hardwood floor or in the middle of a den, a seasoned installer will look for alternate locations, often near utility rooms, stairwells, or closets where slab access is less intrusive. Sometimes a perimeter French drain system or a block wall void can be adapted as a suction pathway, but that should be verified with pressure checks rather than guesswork.

Home additions complicate sub-slab communication. A new slab poured against an old foundation might not share aggregate pathways. I have had to drill through a cold joint to connect the two or run separate suction points. The final post-mitigation test should be placed in the lowest occupied area that connects to both sections, or run two monitors to be safe.

For new construction, passive radon rough-ins are smart and inexpensive compared to retrofits. A passive stack routes from the sub-slab gravel bed or drain tile to the roof. If post-occupancy testing shows elevated levels, adding a fan converts it to an active system with minimal disruption. Builders who include a sealed sump lid, proper sub-slab aggregate, and a clear path for vent piping make life easier for the future homeowner. If you are building, ask your contractor to follow EPA Radon-Resistant New Construction guidelines. In this market, it is a small upcharge with outsized benefit.

Health context without hype

Radon’s link to lung cancer is well-established. Risk rises with higher levels and longer exposure, and smoking compounds the danger. That does not mean a week in a home with 5 pCi/L is cause for panic. Mitigation is about reducing average exposure over months and years, nudging probabilities in your favor. I tell clients that a well-designed Radon system is like a seatbelt. You hope to never need it, but it sits there, working every day, quietly trimming risk.

Some homeowners ask whether air purifiers help. Portable HEPA units do not remove radon gas. They may capture some radon progeny attached to aerosols, but they are not a substitute for source control at the slab. Sealing cracks alone rarely brings numbers down sufficiently, though it helps the primary system do its job. Ventilating with an HRV can lower levels in some homes, yet in St. Louis summers you pay an energy penalty, and in winter you may depressurize the house in ways that increase soil gas flow. Sub-slab depressurization remains the most reliable and economical method here.

Weather, seasons, and the St. Louis quirk factor

Our climate brings two pressures that affect readings. In winter, stack effect pulls air up and out of the house, creating a slight vacuum at the lowest level. That suction can draw more radon from the soil. In summer, heavy air conditioning can create negative pressure in basements, especially if supply and return are imbalanced or if there is duct leakage. Thunderstorms and rapid barometric changes sometimes cause temporary spikes. If you watch a continuous monitor, you can see levels breathe with the weather.

Another local quirk is the prevalence of sumps feeding to exterior footing drains that daylight on sloped lots. If the sump lid is unsealed, the Radon system may short-circuit by pulling outdoor air through that drain instead of under the slab. A clear, gasketed lid with proper pass-throughs for pump cords and discharge solves the issue. Likewise, homes with porous cinder block foundations may benefit from block-top sealing or, in rare cases, a dedicated suction tapping the hollow cores.

What to watch during installation day

You can learn a lot in an hour with a contractor on site. Watch how they prep the suction point. If they pull out just a coffee can of soil and call it good, they may not achieve adequate pressure field extension. I prefer a larger sub-slab void, often 5 to 10 gallons removed, depending on aggregate. When they fire up the shop vac and drill small diagnostic holes, they should measure pressure changes at several spots around the basement, not just at the suction point. That tells you the pressure field is reaching across the slab.

Ask them to show you the U-tube manometer reading after the fan runs for a few minutes. They should annotate what a normal reading looks like for your fan model and what indicates a problem. Photograph the label with the fan model and the date. If they route through a garage to reach the attic, ensure the piping is sealed at the garage ceiling penetration to maintain fire separation, and that the discharge terminates above the roofline, not under an eave where exhaust can be pulled back indoors.

Working with real estate timelines

During a sale, radon becomes a clock. Buyers want safety, sellers fear delays, and inspectors sit in the middle. If a test comes back above 4.0 pCi/L, both sides are best served by moving straight to mitigation rather than arguing about retests that draw out closing. A credible Radon mitigation contractor can usually install within a week. Add two to three days for post-mitigation testing. Many contracts accept an escrow holdback if the calendar is tight. Document the baseline test, the system installation, and the post result. Keep copies in the Radon system seller’s disclosure packet. A clean radon file calms underwriters and keeps signatures moving.

How to choose between similar bids

When two quotes look alike, dig into fan sizing, suction points, discharge termination, and finish quality. One installer may be pricing a low-suction, high-flow fan that is cheap and noisy, while another offers a mid-range fan better matched to your slab’s resistance. Ask what happens if the first post-test is not low enough. Do they include a second suction point at no or reduced cost if needed, or is that a separate change order? Also compare warranty terms. One year on labor and five years on the fan is common. Some companies offer longer coverage that hints at confidence in their design and materials.

Finally, evaluate communication. If an estimator returns calls promptly, explains trade-offs, and provides a written scope that includes cleanup, patching, and test verification, you will likely get similar care from the crew. The cheapest bid can be expensive if it leaves you with a humming pipe off the front porch that does not meet code or results that hang just below 4.0 pCi/L on a cold week and drift higher every January.

A simple homeowner checklist for success

Test correctly first, ideally with closed-house conditions and placement in the lowest livable level. Hire a contractor who measures pressure field extension and can explain fan selection. Seal sumps and obvious slab openings to support the system rather than replace it. Verify performance with a post-mitigation test and keep all records together. Retest every two to three years or after major foundation or HVAC changes.

Common myths and practical truths

I often hear that opening a basement window a crack is a fix. It is not. You may drop a short-term number by diluting basement air, but you are not stopping the source. Once the window closes in winter, levels rebound. Another myth is that brand-new homes are immune. I have measured double-digit readings in new subdivisions where the soil under those tidy slabs had plenty of uranium and the builders skipped a passive stack. Conversely, I have scanned a 1920s brick bungalow with a rubble foundation and found 1.2 pCi/L. The lesson is to test rather than guess.

People also assume bigger fans are better. Oversizing can create condensation problems in vertical risers, increase noise, and pull conditioned air from indoors into the sub-slab, which wastes energy. Proper sizing matters. A well-matched Radon system runs quietly, uses modest power, and delivers stable, low numbers.

Finally, some folks expect an air purifier to solve radon outright. It does not. Capture of decay products is partial at best and does little for gas-phase radon. Source control under the slab is still the primary tool in this region.

Integrating radon mitigation with other home improvements

If you plan to finish a basement, schedule the mitigation first. It is easier to core and route piping before drywall and paint go up. If you are upgrading HVAC, ask the contractor to pressure-balance the system and avoid excessive return-only pathways in the basement that can over-depressurize the lowest level. If you are insulating rim joists, leave access room for potential suction points or piping runs. And if you are replacing windows, remember that tighter shells can raise radon levels by reducing natural leakage. The fix is not to punch holes back in the envelope, it is to let the Radon mitigation system handle soil gas while your house holds conditioned air efficiently.

What “Radon mitigation near me” should deliver in St. Louis

Local context matters. A crew that has worked across St. Louis City and County will already know which neighborhoods are prone to poor sub-slab communication, which municipalities are strict about discharge heights, and how to thread piping on a two-story 1920s brick without leaving a plastic scar on the facade. If you find yourself typing Radon mitigation system or Radon system into search, look beyond ads. Read recent reviews that mention post-mitigation numbers, not just punctuality. Ask neighbors. A contractor who solved a persistent 10 pCi/L basement on your block last year already knows your soil, your slab, and likely your code inspector.

Living with a radon system day to day

After the install, life looks the same. The system hums softly in the background. You might glance at the U-tube manometer once a month, the way you check a sump pump after a heavy rain. In winter, you enjoy the same sealed windows without wondering what you are trapping under your feet. If you host extended family in a newly finished basement, you do it with the quiet assurance that you have addressed a major indoor air risk with a permanent solution.

If you notice the manometer level equalize, or you hear the fan change pitch, act as you would with a sump that stopped after a storm. Call the installer. Fans are mechanical and eventually fail, but replacement is straightforward and quick. Keep a spare lab test kit on a shelf. Every couple years, run it, log the number, and get back to normal.

Radon is a patient hazard. It takes years to matter, which is exactly why homeowners delay. In St. Louis, with our geology and housing stock, waiting is not wise. A simple test and a well-designed Radon mitigation system convert an invisible risk into a solved problem. That is the kind of home improvement that pays you back in a currency more important than curb appeal.

Air Sense Environmental – Radon Mitigation & Testing

Business Name: Air Sense Environmental – Radon Mitigation & Testing
Address: 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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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/.