Why Radon Levels Fluctuate in Homes

If you’ve ever tested for radon more than once, you’ve probably seen it.

• One test reports 3.2 pCi/L or 118.4 Bq/m³
• Another test reports 6.4 pCi/L or 237.8 Bq/m³
• Continuous radon monitor shows levels moving up and down throughout the day

Radon gas entry is not stable. The pressure differences that pull radon into a home change constantly, which causes radon levels to rise and fall throughout the day, the week, and across seasons.

If you’ve noticed your levels swinging from one day to the next, it’s usually due to a combination of the following factors.

Weather Variations

Rain, wind, and barometric pressure affect how radon enters and moves throughout a home or building.

Changes in barometric pressure influence how much radon enters a home. When barometric pressure drops, radon gas can move more easily out of the ground and into buildings. This is why radon levels sometimes spike before or during storms.

Rain and snow have mixed impacts. In some cases, wet or frozen soil can temporarily seal or “cap” the ground surface and force more radon toward a home's foundation. Rain is often accompanied by wind. Strong winds can create pressure differences around a home which can either “push” radon out or “draw” radon inside the home.

Outdoor Temperature

The difference between indoor and outdoor temperature creates a pressure pull known as the stack effect (or chimney effect), which contributes to the seasonal fluctuations of indoor radon levels.

• During winter: With colder outdoor temperatures, warm air rises and escapes through the upper levels of the home. This creates a vacuum at the lowest level, pulling in cold air as well as radon from the soil.
• During summer: When indoor air is cooler than outdoor air, the effect is often reversed or neutralized, though air conditioning can sometimes create pressure changes that still draw gas in.

Everyday Activities

Normal household activities influence radon concentrations such as:

• Running bathroom or kitchen exhaust fans
• Using clothes dryers
• Operating fireplaces
• Opening and closing windows
• HVAC system operation

All of these activities change air pressure and airflow within a home. Even something as simple as turning on a powerful exhaust fan can temporarily increase the amount of radon gas being pulled into your home.

Home Construction Features

Every home interacts with radon differently. Two houses next door to each other can have very different radon levels due to:

• Foundation type
• Soil permeability around the home
• Drainage systems
• Presence of sump pits
• Air leakage pathways
• Type of building materials

Renovations or changes to a home, such as finishing a basement, installing new windows, or improving insulation will also change airflow patterns and influence radon levels.

Importance of Understanding Why Radon Fluctuates

Radon risk is based on cumulative exposure over time. Long-term exposure to high radon levels is the second leading cause of lung cancer after smoking and the leading cause of lung cancer among non-smokers.

By understanding radon fluctuations, you can make the most informed decisions about radon testing type. For example, short-term radon test results can differ. Because radon fluctuates naturally, short-term tests capture only a snapshot in time. A short-term test conducted over 2 to 4 days might be affected by weather, temperature, or household activity conditions that produce unusually high or unusually low radon readings.

Take action to address concerns that stem from radon fluctuations with:

• Long-term radon testing (90 days or more) for the most accurate result
• Continuous home radon monitoring to observe trends
• Retesting as recommended by the EPA and Health Canada of every two years and especially after home renovations

When elevated radon levels are identified, installing a radon mitigation system by a certified radon mitigator is the safest way to protect your family from continued high exposure.

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