# National Radon Action Month: Why St. Louis Homes Should Test Before January

- **URL:** https://airsenseenvironmental.com/national-radon-action-month-st-louis/
- **Published:** 2026-10-23

January is National Radon Action Month, Radon Action Week falls in the third week of October, and the reason both sit in the cold half of the year is that heating season is when indoor radon is at its most representative and its highest. If you are going to test once, test while the furnace is running. For homes in St. Louis, MO and throughout St. Louis County, St. Charles County, Jefferson County, and the Madison and St. Clair County side of the metro, that window is open now. Missouri offers residents a free test kit. Illinois publishes a low-cost kit list and a public map of measured results by county and zip code. Neither program is well known, and both are the cheapest way to answer the question. This guide covers what the two observances are, why the season matters physically, where to get a kit on each side of the river, what to do with the result, and how to get ahead of the January rush. What is National Radon Action Month? January. The EPA designates January as National Radon Action Month, and its stated aim is to increase public awareness of radon, promote radon testing and mitigation, and advance the use of radon-resistant new construction practices. The same EPA page names the second observance: Radon Action Week is the third week in October, with some communities extending indoor air quality topics through the rest of the month. Two observances, three months apart, bracketing the heating season. That is not a coincidence, and it is the practical takeaway for a homeowner: October is when you start, January is when the whole country is reminded, and the testing window runs through both. Why does the season matter for radon testing? Because the force that pulls radon into a house is strongest when it is cold outside and the house is closed. Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It enters buildings through foundation cracks, slab penetrations, sump pits, crawl spaces, and utility openings. What draws it in is a pressure difference: warm indoor air rises and escapes at the top of the house, and the slight negative pressure left behind at the bottom pulls replacement air from the ground beneath the slab. Three things happen from October onward that strengthen that effect: The temperature difference widens. A bigger indoor to outdoor gap means a stronger stack effect. The house stays closed. Windows shut, less dilution. The soil changes. Saturated or frozen ground caps the surface and pushes more soil gas toward the one warm, low-pressure opening available, which is your foundation. The result is that the same house can measure meaningfully lower in July than in January. We cover the mechanism and the size of the swing in radon levels: winter vs. summer. The practical implication: a winter result is the one to design around, and a borderline summer result deserves a winter confirmation. Where do Missouri and Illinois homeowners get a radon test kit? MissouriIllinoisProgramMissouri DHSS radon programIEMA-OHS radon programKit availabilityFree kit for Missouri residents, limit one per household, coupon code TESTINGLow-cost kit list published by the state, plus a measurement laboratory price listLocal dataInteractive radon maps and test results at or above 4 pCi/LInteractive radon map by county or zip codeProfessional licensingNo state licence required for radon contractors; use the national certificationsState licence required under the Radon Industry Licensing Act, with a public licensee lookupReal estate rulesStandard disclosure practiceRadon Awareness Act requires the seller to give the buyer the state pamphlet and disclosure form A note on the Illinois map, in IEMA-OHS's own words: it is not intended to determine whether a home in a given county or zip code should be tested, because elevated levels have been found throughout the state, and all homes should be tested regardless of location. The same logic applies on the Missouri side. Zone maps describe geological potential, not your particular house. The EPA adds that free kits are sometimes available from local or county health departments and state radon programs, and that the National Radon Program Services at Kansas State University sells kits and operates 1-800-SOS-RADON. Its guidance on getting a test kit has the details. What does the result actually mean? The EPA recommends fixing a home at 4.0 pCi/L or higher, and considering a fix between 2.0 and 4.0 pCi/L, because there is no known safe level of radon exposure. Two reference points give the number scale: the average indoor concentration in the United States is about 1.3 pCi/L, and outdoor air averages about 0.4 pCi/L. On the health side, the EPA estimates that radon in indoor air causes about 21,000 lung cancer deaths each year in the United States, that lung cancer is the only health effect definitively linked to radon exposure, and that smokers are at higher risk of radon-induced lung cancer. Those are population-level estimates and that is how they should be read. No test result predicts what will happen to any individual person. The EPA's three-step protocol is the right way to act on a first number: Take a short-term test. If the result is 4 pCi/L or higher, follow up. Follow up with a long-term test for a year-round average, or a second short-term test if you need an answer quickly. If the first result is more than twice the action level, take the second short-term test immediately. Fix the home if the long-term result is 4 pCi/L or more, or if the average of the two short-term tests is 4 pCi/L or higher. For placement and duration, our guide on where to place a radon detector and our breakdown of how long you should test for radon cover the specifics. What should you do during Radon Action Week in October? Four things, none of which take a weekend. Order the kit. Missouri's is free. Illinois publishes low-cost options. Do it before the January rush, when every lab and every mitigation calendar in the metro fills up. Close the house 12 hours before you start. For a short-term test of two or three days, the EPA says close windows and outside doors at least 12 hours before the test begins and keep them closed throughout, except for normal entry and exit. Skip the test entirely during unusually severe storms or unusually high winds. If you already have a mitigation system, look at the manometer. Two unequal fluid columns mean the fan is pulling. Level columns mean it is not. Then check the exterior discharge and the fan housing for leaves and nests before the first freeze. Retest if it has been more than two years. That is the EPA's standing recommendation, mitigated home or not. Our guide to how often you should test for radon has the trigger list. Why not just wait for January? Because January is when everyone else calls. National Radon Action Month generates real demand. Labs slow down, measurement professionals book out, and mitigation schedules compress, all in the coldest weeks of the year, which is also when exterior installation work is hardest to schedule around weather. A home tested in late October has its result in early November and, if mitigation is warranted, a system in before the deep cold. There is also a real estate reason. Spring listings in the St. Louis metro start going up in February and March, and a radon result in hand before you list is a stronger position than a result produced under inspection deadline pressure. Sellers who already know their number, and who can show a system and a verification test if one was needed, do not lose negotiating room to a surprise. If that is your situation, what to do if your radon test comes back high covers the sequence. Frequently asked questions When is National Radon Action Month? January. The EPA designates it annually to promote radon awareness, testing, mitigation, and radon-resistant new construction. When is Radon Action Week? The third week in October, per the EPA. Some communities extend related indoor air quality programming through the rest of October. Is winter the best time to test for radon? Heating season is when a short-term test is most likely to capture the worst case, which is the number worth designing around. Testing at other times is still valid, but a borderline warm-weather result deserves a winter confirmation. Can Missouri residents get a free radon test kit? Yes. The Missouri Department of Health and Senior Services offers a free kit to Missouri residents, limited to one per household, using the coupon code on its radon program page. Does Illinois require a licensed radon professional? Yes. Illinois licenses radon measurement and mitigation professionals through IEMA-OHS under the Radon Industry Licensing Act, and maintains a public list of licensees. Missouri does not have a state licensing requirement, so look for NRPP or NRSB certification there. What radon level requires action? The EPA recommends fixing a home at 4.0 pCi/L or higher and considering a fix between 2.0 and 4.0 pCi/L. Confirm a first short-term result at or above the action level with a follow-up test before deciding. Get tested before the January rush Testing is the cheap part of this, and October is the right month for it. Air Sense Environmental provides radon testing and designs and installs radon mitigation systems across the greater St. Louis metro on both sides of the river, from our base in Edwardsville. Call 314-664-9807 or request a free estimate.