Understanding Seasonal Changes in Radon Levels in Milwaukee, WI

Do Radon Levels Change With the Seasons in Milwaukee, WI?

Yes, radon levels inside homes can change with the seasons, sometimes significantly. In Milwaukee, WI, this seasonal variation is mainly driven by shifts in weather, temperature, and how homes are ventilated throughout the year. Understanding when and why these changes happen helps local residents better interpret test results and decide when testing and mitigation actions make the most sense.

Why Are Radon Levels Higher in Winter?

Radon tends to be highest indoors during the winter months in Milwaukee. This increase is largely due to the way homes are managed to keep out the cold:

• Windows and doors are kept closed, limiting natural ventilation.
• Heating systems are used, which circulate indoor air without bringing in outside air.
• Frozen ground and snowpack can make it harder for radon to vent harmlessly to the atmosphere, instead trapping it underground where it may seep into basements and lower levels.

These conditions increase the "stack effect," where warm air rises and escapes from the upper portions of a house, creating a pressure difference that draws more soil gases, including radon, through cracks and gaps at the foundation.

Can Radon Levels Drop During Warmer Months?

Radon levels often decrease in local homes during late spring, summer, and early fall. The primary reasons:

• Windows and doors are more likely to be open, improving ventilation.
• Air conditioning systems (especially those that circulate fresh air from outside, not just recirculated indoor air) can dilute indoor radon concentrations.
• Ground is not frozen, allowing more radon to dissipate outdoors before entering the home.

That said, elevated levels can still occur, especially in homes with tight building envelopes or central air conditioning that recirculates rather than exchanges air.

Are There Times When Radon Testing Is Most Accurate?

Short-term radon tests are most likely to show the highest, and therefore most critical, readings during the colder part of the year—typically from late October through early April in Milwaukee. The Environmental Protection Agency (EPA) and state health departments often recommend testing during this period because it reflects “worst-case” exposure.

However, long-term radon tests (lasting 90 days to a year) provide the most complete picture, averaging out seasonal highs and lows. These are especially useful for homes with variable ventilation patterns or when occupancy changes throughout the year.

How Does Milwaukee’s Climate and Housing Stock Affect Radon Fluctuations?

Milwaukee experiences distinct, sometimes extreme, seasonal swings. Winters are cold and snowy, and many homes have basements or crawl spaces—areas prone to radon entry. Typical building practices in the community, such as older foundations, finished basements, and the use of sump pumps, can each influence how much radon seeps in and how indoor air is distributed.

• During winter, many area households use fireplaces or wood stoves; this increases air movement up chimneys, further lowering indoor pressure and potentially pulling in more soil gases.
• High winds and storms can also temporarily increase radon entry, regardless of temperature, by altering indoor air pressure.

What Are Common Misconceptions About Seasonal Radon Levels?

Residents sometimes believe radon is only a concern during winter or that testing in spring or summer is pointless. In reality:

• Some homes in Milwaukee have been found to have consistently high levels year-round, often due to specific foundation issues or site conditions.
• Closing up a house during summer (running central air without outdoor air exchange) can also cause indoor radon to rise.
• Everyday household habits, like using bathroom or kitchen exhaust fans, can briefly create lower interior pressure and draw in more radon, regardless of season.

What If a Radon Test Shows Different Results in Each Season?

It’s not uncommon for a home in Milwaukee to test below the EPA action level in summer but exceed it in winter. If a single test was done during a low-ventilation period and results were borderline, a follow-up test in a different season or a long-term average can clarify any potential risk.

If a home’s average radon level is at or above the EPA guideline (4.0 picocuries per liter), mitigation measures should be considered, regardless of when the highest readings occur.

Tips for Managing Seasonal Radon Risks in Area Homes

• Test for radon at least once, ideally during the colder months, to catch possible high readings.
• For the most accurate understanding, use a long-term test kit spanning several months.
• Retest after any significant renovations, HVAC changes, or foundation repairs, as these may affect radon entry and movement.
• Remember that results can change over time due to settling, new cracks, or changes in how the home is ventilated.

Awareness of seasonal changes helps area families make informed decisions about home safety, ensuring year-round protection from radon exposure.