Why Your St. Louis Home Needs a Radon Test and How to Start

If you live in St. Louis, Missouri, and you haven’t tested your home for radon yet, you are not alone. Many homeowners assume radon is a problem that happens somewhere else, maybe in a basement with a dirt floor or in an old house with obvious cracks. The reality is less dramatic and far more common. Radon is a naturally occurring radioactive gas that seeps up from the soil, and it can enter any home, regardless of age or condition. The only way to know if your home has elevated radon levels is to perform a home radon test.

I have spent years working in indoor air quality, and I have seen the same pattern repeat: a family buys a radon test kit from a hardware store, gets a result that surprises them, and then scrambles to understand what to do next. A home radon test is not complicated, but doing it correctly matters. The difference between a reliable result and a misleading one often comes down to choosing the right test and following the instructions.

What Radon Is and Why It Matters in St. Louis

Radon comes from the natural decay of uranium in soil and rock. It moves up through the ground and into the air we breathe. When radon gets trapped inside a building, it can accumulate to levels that pose a health risk. The EPA has identified radon as the second leading cause of lung cancer, after smoking. For non-smokers, it is the number one cause.

St. Louis and much of Missouri sit on geology that can produce significant radon. The EPA has mapped radon zones across the country, and St. Louis County and the surrounding areas fall into Zone 1, meaning the average indoor radon level here is expected to be above the action level of 4 picocuries per liter. That does not mean every home has a problem, but it means the risk is high enough that every home should be tested. I have tested homes in Cottleville, Webster Groves, and downtown Clayton that showed low levels, and others within the same neighborhood that needed mitigation. The only pattern is that there is no pattern.

How a Home Radon Test Works

A home radon test measures the concentration of radon in the air over a set period. There are two main approaches: short-term and long-term. A short-term radon test typically lasts two to seven days and uses a device such as a charcoal canister or a continuous radon monitor. A long-term test runs for more than 90 days and gives a better picture of the annual average.

For a first screening, most people start with a short-term test. If the result comes back below 4 pCi/L, you might choose to test again later or move to a long-term test for peace of mind. If the result is above 4 pCi/L, you should take action. That action usually involves a follow-up test to confirm the level, and then planning for radon remediation.

There is one catch: the test needs to be done under closed-house conditions. That means keeping windows closed, doors shut except for normal entry and exit, and avoiding fans or ventilation that pull in outside air. The test should be placed in the lowest lived-in level of the home, often a basement or a first-floor room if there is no basement. You also want to avoid placing it in a crawl space unless people actually spend time there. Radon levels can vary significantly between a finished basement and an unfinished crawl space, so think about where your family actually lives.

Continuous Radon Monitors vs. Test Kits

You have probably seen radon test kits at hardware stores or online. These are usually charcoal-based and are sent to a lab after exposure. They are affordable and work fine for a screening, but they have limitations. The lab result tells you an average over the test period, but it cannot tell you whether levels spiked during a storm or dropped when you opened a window.

A continuous radon monitor, on the other hand, takes readings every hour or so and records the data. Companies like Air Sense Environmental use these monitors for professional testing. The advantage is clear: you get a time-stamped record of radon levels throughout the test. If a reading jumps at 2 AM and stays high, you know something happened, maybe the furnace kicked on and changed air pressure, or a storm passed through. That kind of detail helps a professional interpreter tell you whether the average is trustworthy or whether the test conditions were compromised.

For a one-time check, a test kit might be enough. But if you are preparing to buy a home, or if you already have a borderline result, a continuous monitor test is worth the extra money. It removes a lot of the guesswork.

What to Do With Your Results

If your home radon test shows a level at or above 4 pCi/L, the EPA recommends fixing your home. The standard fix is a radon mitigation system, most often a type of soil suction called sub-slab depressurization. A pipe is run from under the basement slab or crawl space floor up to the roofline, with a small fan that pulls radon-laden air from beneath the house and vents it safely above. This system is not cheap, but it is effective. Most homes see radon levels drop to well below 2 pCi/L after installation.

There are other options, such as sealing cracks and improving ventilation, but those rarely bring levels down enough on their own. Sub-slab depressurization is the gold standard for a reason: it addresses the source rather than just the symptoms.

If your test shows levels between 2 and 4 pCi/L, you have a choice. Some people fix it anyway, especially if they have children or someone who smokes in the home. Others decide to retest in a different season or switch to a long-term test before making a decision. I have seen homes in the 3 pCi/L range that stayed there across multiple tests, and the owners chose to install mitigation for the peace of mind. There is no wrong answer, but the lower you go, the lower your long-term risk.

The Role of a Professional Radon Tester

A professional radon tester brings more than just equipment. They understand how to position the test for the most representative reading, how to handle conditions like high humidity or radon interference from appliances, and how to interpret results in context. When I work with Air Sense Environmental, I have seen them walk homeowners through the entire process, explaining why the continuous radon monitor was placed where it was and what the numbers mean as they come in.

For a home inspection related to a real estate transaction, professional testing is almost always required by the buyer or lender. A test kit you buy yourself might not be accepted because the chain of custody is not documented. A professional tester provides a report that includes the monitor serial number, calibration date, and a clear statement of results. That report holds up in negotiations.

Even if you are not selling, hiring a professional gives you confidence that the test was done right. I have seen too many homeowners get a borderline result from a kit, then spend weeks wondering whether they left the basement window cracked. With a continuous monitor, that ambiguity disappears.

Practical Tips for Your First Home Radon Test

If you decide to start with a DIY test, here are a few things to keep in mind:

Choose a test kit that is labeled as EPA-approved or meets EPA standards.
Place the test in the lowest lived-in level of the home, at least 20 inches above the floor and away from drafts, heat sources, and humidity.
Keep the house closed for at least 12 hours before starting the test and throughout the test period.
Do not move the test once it starts. If you bump it or the kids knock it over, stop the test and start over.
Send the test to the lab as soon as the exposure period ends. Delays can affect the result.

If you would rather hire someone, look for a tester who uses a continuous radon monitor and who is certified through a recognized program like the National Radon Proficiency Program or the American Association of Radon Scientists and Technologists. A good tester will also explain the results in plain language and help you understand your next steps.

Final Thoughts

Testing for radon is one of the few home maintenance tasks that directly affects your health. The test itself is simple, the cost is low, and the information you get can guide a decision that might save your life or the life of someone you love. In St. Louis, Missouri, where the geology is prone to radon, there is no good reason to skip it. Whether you use a test kit from the hardware store or hire a professional like Air Sense Environmental to run a continuous radon monitor, the important thing is to start. A home radon test is the first step toward knowing your risk and doing something about it.