--- title: The Best Time of Year to Test for Radon canonical: "https://radonmitigationyorkpa.net/radon-guide/best-time-to-test-for-radon/" pubDate: "2026-10-01T00:00:00.000Z" updatedDate: "2026-10-03T00:18:00.000Z" author: Radon Mitigation York PA description: "You can test for radon any time of year. Learn why winter results often run higher, why January is Radon Action Month and how to time your test." --- # The Best Time of Year to Test for Radon The best time to [schedule radon testing](/services/radon-testing/) is now, in any season. Winter results often run higher because the house stays sealed and heated air rising inside pulls more soil gas up from the ground, which is one reason January is National Radon Action Month. A summer test still counts, and a high summer result should be taken seriously. ## Why radon levels change with the seasons Radon comes from uranium breaking down in the soil and rock under your home. It moves into the house through cracks, gaps around pipes, sump pits and other openings in the foundation. How much gets in depends a lot on air pressure inside the house compared with the soil. ### The stack effect in winter When you heat your home, warm air rises and leaks out through the upper floors and attic. That creates slightly lower pressure in the lower part of the house. The low pressure acts like a gentle vacuum, drawing soil gas in through the foundation. This is called the stack effect, and it is strongest when the gap between indoor and outdoor temperatures is biggest. ### Closed windows In winter, windows stay shut for months. Less outdoor air means radon that gets in has fewer ways out. Both factors tend to push winter readings up. ### Frozen or wet ground Frozen or saturated soil at the surface can limit how much radon escapes into the open air around the house. Some of that gas may move toward the house instead, where the soil under the slab stays dry and loose. ### Summer conditions In summer, open windows and doors bring in fresh air and the stack effect is weaker. Readings are often lower. Air conditioning changes the picture again, because a closed, cooled house can still pull soil gas in. Some homes even test higher in summer, which is why no season gives a guaranteed result. ## Why January is National Radon Action Month The [EPA](https://www.epa.gov/radon) promotes January as National Radon Action Month. It is a good time to test because homes are closed up and heating systems are running, so a short-term test reflects higher-risk conditions. In past years, PA DEP and the American Lung Association have handed out free test kits to Pennsylvania residents around this time while supplies last. ## Is a winter test more accurate? Not more accurate, but often more cautious. A short-term test measures the conditions during the days it runs. If you test in January, you are measuring your home at what is often its worst. If that result is low, you can feel more confident. If it is high, you know there is a problem. A summer test might read lower than your yearly average. That does not make it wrong. It means one short test is a snapshot. If a summer result comes in between 2 and 4 pCi/L, consider retesting in the heating season or running a long-term test. ## The best time depends on your goal ### Buying or selling a home Test when the sale requires it. A home sale does not wait for winter. Closed-house conditions help make a test in any season more consistent, because windows and doors stay shut 12 hours before and during short-term tests under four days. ### Testing your own home for the first time Test as soon as you can. Waiting for winter means months of unknown exposure. If you want the strongest single snapshot, test in the heating season. If you want the truest average, use a long-term test that covers more than 90 days. ### After installing a mitigation system Test no sooner than 24 hours after the system starts and within 30 days, per EPA guidance. Season does not matter for this clearance test. After that, the EPA recommends retesting every two years. Alternating between a winter and a summer retest can show how the system performs across seasons. ## Weather to avoid during a short-term test The EPA advises against running a 2 to 3 day short-term test during severe storms or periods of unusually high winds. Big swings in air pressure can push radon levels up or down for a few hours or days. If a major storm is in the forecast, consider moving the test or running it longer. ## Testing in York York sees cold winters and humid summers, so seasonal swings can be noticeable here. Many homes in and around the city are older, with stone or block foundations and basements that sit deep in the soil. These homes tend to feel the stack effect strongly in winter. York County is also in EPA Radon Zone 1, the highest potential category. ## What to do after you get your result Once you have a number, the next step is knowing what it means. Our guide on [how to read your radon test results](/radon-guide/radon-test-results-explained/) covers the 4.0 pCi/L action level, the 2 to 4 range and when to follow up. ## Key takeaways - You can test for radon any time of year. - Winter results often run higher because of the stack effect and closed windows. - January is National Radon Action Month. - A summer result between 2 and 4 pCi/L is worth retesting in the heating season. - Avoid short-term tests during severe storms or very high winds. - Do not delay a first test waiting for the "right" season. ## Frequently Asked Questions ### Should I wait until winter to test? No. Test now. If the result is borderline, retest during the heating season or use a long-term test. ### Can rain affect a radon test? Yes. Heavy rain and saturated soil can change how radon moves around the foundation, so results may shift during and after big storms. ### Does a high summer result mean winter will be worse? Often, but not always. Every house behaves differently. A long-term test is the best way to see your real average across seasons. ## Test your home any season Whether it is January or July, you can book radon testing in York, PA with a certified continuous monitor. Call [(717) 356-3035](tel:+17173563035) any time for a same-day callback.