Why Every St. Louis Home Needs a Radon Gas Test

When I bought my first house in St. Louis, I did all the usual things. I hired a home inspection, checked the roof, and looked for signs of water in the basement. What I did not do was schedule a radon gas test. I figured radon was someone else’s problem, maybe a concern for people in other parts of the country. I was wrong. Radon is a real issue in Missouri, and the only way to know if your home has a problem is to test for it.

Radon comes from the natural decay of uranium in soil and rock. It moves up through the ground and into buildings through cracks in foundations, gaps around pipes, and other openings. You cannot see it, smell it, or taste it. The US EPA ranks radon as the second leading cause of lung cancer in the United States, and it is the number one cause among non-smokers. For anyone living in an area with moderate to high radon potential, and much of Missouri, including St. Louis, falls into that category, a radon gas test is not an optional extra. It is a necessary step in protecting your indoor air quality.

What a Radon Gas Test Actually Measures

A radon gas test measures the concentration of radon in the air inside your home. The result is reported in picocuries per liter (pCi/L). The US EPA has set an action level at 4.0 pCi/L. If your test result is at or above that number, you should take steps to reduce the radon level. But even levels between 2.0 and 4.0 pCi/L carry some risk, and the EPA recommends that homeowners consider mitigation in that range as well.

There are two main ways to test: a short-term test and a long-term test. A short-term test stays in your home for two to seven days. It gives you a quick snapshot, but radon levels can vary day to day and season to season. A long-term test runs for more than 90 days and gives a better picture of the annual average radon concentration. For a home purchase or sale, a short-term test is often used because of time constraints. But for your own peace of mind, a long-term test is more reliable.

Testing Options: Kits vs. Professional Service

You can buy a radon test kit at a hardware store or online. Most of these are passive devices, meaning they collect radon or its decay products without any power source. Two common types are the charcoal canister and the electret ion chamber. The charcoal canister absorbs radon over a few days and is then sent to a lab for analysis. The electret ion chamber uses a static charge to measure radon and is also sent to a lab. Both are valid methods, but they have limits. They can be affected by air movement, humidity, and placement. If you place the kit in the wrong spot or open a window during the test, the result may not be accurate.

For a more reliable result, many homeowners turn to a professional service like Air Sense Environmental. A professional radon gas test uses a continuous radon monitor. This is an electronic device that takes readings at set intervals, often every hour, over the test period. It gives a detailed record of how radon levels change throughout the day. A continuous radon monitor can detect spikes that a passive device might miss. It also reduces the chance of human error in placement and handling. The result is a more accurate and defensible measurement.

If you are buying or selling a home, a professional test carries more weight. A radon test kit might give you a number, but a professional test gives you a clear report with time-stamped data. That can make a difference in real estate negotiations or in deciding whether to install a radon mitigation system.

What to Do With Your Results

If your radon gas test shows a level below the action level, you are in a good spot. But radon levels can change over time. Home renovations, foundation settling, or changes in the soil can affect how radon enters your home. The US EPA recommends testing again every two years, or after any major structural work.

If your test result is at or above 4.0 pCi/L, the next step is radon mitigation. A radon mitigation system typically involves installing a vent pipe and fan that pulls radon from beneath the house and exhausts it safely above the roofline. This is called sub-slab depressurization, and it is the most common and effective method. A qualified contractor will assess your home’s foundation and soil conditions to design a system that works. In new construction, radon resistant construction techniques can be built in from the start, which is far cheaper than retrofitting later.

It is worth noting that radon reduction systems are not a one-size-fits-all solution. The right approach depends on your home’s design, the soil type, and the severity of the radon problem. A professional radon tester can help you understand your options and connect you with a mitigation specialist if needed.

Why St. Louis Homeowners Should Pay Attention

St. Louis sits on a mix of soils, including glacial till and limestone, that can produce radon. The radon map published by the US EPA and state agencies shows that much of Missouri, especially the eastern half, is in Zone 1, which means predicted average indoor radon levels above 4.0 pCi/L. That does not mean every home in St. Louis has a high radon level, but it does mean the potential is there. The only way to know for sure is to test.

I have seen homes in the same neighborhood with very different radon levels. One house might come in at 2.0 pCi/L, while the house next door reads 8.0 pCi/L. Soil permeability, foundation type, and even the way the house sits on its lot can all play a role. That is why a neighbor’s test result is not a substitute for your own radon gas test.

If you are planning a home inspection, ask your inspector whether radon testing is included. Many general home inspectors do not carry a continuous radon monitor and may offer only a charcoal canister kit. If you want a more thorough picture, consider hiring a specialist who focuses on residential radon testing. Companies like Air Sense Environmental provide professional testing using continuous monitors, and they can explain the results in plain language.

A Few Practical Tips for Testing

If you decide to test on your own, follow the instructions carefully. Place the test in the lowest livable level of the home, away from drafts, direct sunlight, and high humidity. Keep windows and doors closed as much as possible during the test period, especially for short-term tests. Do not move the device once it is placed.

If you hire a professional, ask what kind of radon detector they use. A continuous radon monitor is the gold standard, but not all monitors are the same. Look for one that is calibrated regularly and meets US EPA performance standards. The professional should also be able to tell you about the test duration, whether they will leave the monitor in place for a full 48 hours or longer, and what the report will look like.

One thing I have learned is that a radon gas test is not a one-and-done event. Even after you mitigate, you should test again to confirm the system is working. Many radon mitigation systems come with a manometer or warning device that shows if the fan is running, but a follow-up test is the only way to know the radon level has actually dropped.

Bringing It All Together

Radon is a natural hazard that we can manage. The first step is knowledge, and that comes from testing. Whether you choose a radon test kit or a professional service, the important thing is to do it. The cost of a test is small compared to the long-term health risk of living with high radon. For homeowners in St. Louis, Missouri, where the geology is favorable to radon production, a radon gas test should be part of any home maintenance routine.

I have tested my own home, and I recommend it to anyone who asks. The process is straightforward, the results are clear, and the next steps are actionable. If your test shows a high level, you can fix it. If it shows a low level, you have peace of mind. Either way, you are better off than not knowing at all.