What Time of Year Is Radon Highest?
Radon is often highest in winter, when closed windows, heating, and pressure differences can reduce air exchange and draw more soil gas indoors. But levels vary by home, weather, and ventilation, so testing over time gives a clearer picture than relying on the season.
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Radon is often highest in winter, when closed windows, heating, and pressure differences can reduce air exchange and draw more soil gas indoors. Levels still vary by home, weather, and ventilation, so monitoring over time gives a better picture than assuming every home peaks in the same season.
What time of year is radon highest in many homes?
Radon is often higher during colder months, especially in homes that stay closed up. Warm indoor air can rise and escape through upper parts of the building, changing pressure and pulling soil gas through openings near the foundation.
That pattern isn't universal. A home's foundation, heating, ventilation, soil, and local weather all affect readings, and some homes may have higher levels in another season.
A single seasonal test shows conditions during its testing period. If you want to understand your home's typical pattern, use longer-term monitoring and compare readings over time.
Why can winter raise indoor radon?
Winter can increase the pressure difference between a home and the soil beneath it. That can draw radon through cracks, utility openings, sump areas, and other paths in contact with the ground.
People also tend to close windows and doors in cold weather. Less outdoor air exchange can allow radon to build up indoors, though mechanical ventilation and individual home conditions can change the result.
The EPA's radon guidance recommends testing homes because radon levels vary from house to house. Season alone can't tell you whether a particular home has a problem.
Can radon be high in summer too?
Yes, radon can be high in summer, even if winter readings are higher in many homes. Air conditioning, open windows, fans, storms, and changes in soil moisture or pressure can shift how much radon enters or remains indoors.
Don't skip testing because it's warm outside. A test can show whether levels were raised under current conditions, while repeated or continuous measurements can reveal more of the home's changing pattern.
For context about room placement, see whether radon levels are higher in the basement. Radon often enters from the ground, but a basement reading doesn't automatically describe every level of the home.
How should you compare seasonal radon readings?
Compare readings from the same location and pay attention to the time period each average covers. Moving a monitor between rooms or floors makes it harder to tell whether a change came from the season or the placement.
Write down notable changes in ventilation, heating, weather, or room use. Short-term spikes can occur, while a long-term average helps show whether raised readings persist.
A radon monitor with trend graphs can make seasonal patterns easier to follow. The Airthings Corentium Home 2 displays short- and long-term averages and connects to an app with graphs.
The Airthings Wave Radon provides daily, weekly, monthly, and yearly measurements through its app, which can help you review changes across seasons.
Use the same placement and follow the device instructions when comparing readings. A monitor helps you observe trends, but it doesn't replace testing or follow-up steps recommended by public health guidance.
Where should you measure radon?
Measure in a regularly used room on the lowest lived-in level, following the test or monitor instructions. Avoid placing a device where drafts, direct sunlight, high humidity, or nearby equipment could affect its readings unless the instructions allow it.
A basement can be useful to test, but choose the location based on how the space is used and what question you're trying to answer. If you're monitoring a crawl space, review whether a radon detector can work in one before placing a device there.
For a display and Wi-Fi connection, Airthings View Radon measures radon along with humidity and temperature, and provides app and dashboard graphs and notifications.
The Ecosense EF100 is battery powered and has an always-on display with current readings, averages, and historic highs and lows. Its Bluetooth app can store data and show trends.
What should you do if a reading is high?
Follow the test instructions and public health guidance to confirm a high result. A single reading can be affected by conditions during the test, and the recommended response depends on the result and the guidance where you live.
Don't wait for a particular season to act on a concerning reading. Testing and follow-up can happen year-round, and a qualified radon professional can advise on mitigation options if raised levels are confirmed.
If you're choosing a device for ongoing measurements, our guide to the best radon monitor for home use explains what to consider. For a broader overview of placement and features, see how to choose a home radon monitor.
How can you track seasonal radon changes?
Keep the monitor in one suitable location, use its averages and history, and note major changes in ventilation or heating. Winter is a useful time to pay attention to radon, but no season guarantees a low or high reading.
Test according to public health guidance, and confirm raised results before deciding what to do next.
If you need to focus on a particular room, read whether radon levels are higher in the basement or how a detector may work in a crawl space. For continuous monitoring options, compare home radon monitors.
Frequently asked questions
Is radon always higher in winter?
No. Winter readings are often higher in some homes, but radon can rise in any season as soil, weather, building pressure, and ventilation change.
A winter result doesn't predict every room or the rest of the year.
Measure where you spend time and consider longer-term monitoring to see your home's pattern.
Should I test for radon in summer?
Yes. You can test in any season, and a summer reading shows conditions during that period.
Windows, fans, air conditioning, and weather can affect indoor levels, so follow the test instructions and don't treat one seasonal result as a full-year average.
Retest or monitor over time if you need a broader view.
How long should I monitor radon?
Monitor long enough to see how readings change, and use the device instructions to interpret short- and long-term averages. Radon can vary from day to day, so a brief reading may not represent long-term exposure.
If a test result is high, follow public health guidance on confirmation and next steps.
Can weather make radon levels rise?
Yes. Changes in temperature, wind, rain, and air pressure can affect how soil gas enters and moves through a home.
Weather is only one influence, and the effect depends on the building and its ventilation.
Track readings alongside conditions, but use testing guidance rather than trying to predict radon from a forecast.
