The UK has been experiencing a spell of unusually hot weather.
Windows are open for longer, fans are running constantly, and many homes and workplaces are trying to stay cool however they can.
But while most people are focused on temperatures, there’s another indoor environmental factor that can also be affected by seasonal conditions, radon gas.
As awareness of radon continues to grow across the UK, one question often comes up during warmer weather:
“Is summer a bad time to test for radon?”
The answer is more nuanced than many people realise.
What Is Radon?
Radon is a naturally occurring radioactive gas formed by the decay of uranium in rocks and soil.
It can enter buildings through:
- floors
- walls
- service penetrations
- cracks and gaps in contact with the ground
Because radon is colourless and odourless, the only way to detect it is through specialist testing.
Long-term exposure to elevated radon concentrations increases the risk of illness, including from diseases such as lung cancer, making it an important indoor air quality issue for both homes and workplaces.
How Hot Weather Can Affect Indoor Radon Levels
Buildings behave differently in summer.
During hotter weather:
- windows and doors are often opened more frequently
- ventilation rates increase
- heating systems are switched off
- indoor and outdoor temperature differences reduce
These changes can help dilute radon concentrations indoors and limit how much is drawn in from the ground via the “stack effect”, meaning levels recorded during hot weather may sometimes appear lower than they would during colder months.
This is one reason why radon testing is often associated with autumn and winter, when buildings are more sealed and ventilation is reduced.
But that does not mean summer testing is pointless.
The Problem Isn’t Summer Testing, It’s Short-Term Interpretation
Radon levels naturally fluctuate throughout the year. That’s exactly why UK guidance recommends long-term testing wherever possible.
A properly conducted 3-month passive radon test accounts for seasonal variation, changing occupancy patterns, weather conditions and day-to-day fluctuations.
In other words, a long-term test helps smooth out the impact of temporary weather conditions like heatwaves. The issue arises when people rely too heavily on very short-term tests, quick readings or isolated measurements during unusual weather.
Without context, results obtained during periods of unusually high ventilation may underestimate the property’s longer-term annual average.
Why You Shouldn’t Wait Until Winter to Test
One misconception is that there’s “no point” testing during summer.
Radon testing can begin at any time of year.
Delaying testing for months can simply postpone important information about the building.
Starting a long-term test now still allows:
- seasonal variation to be considered
- results to be adjusted appropriately where relevant
- and a clearer understanding of overall exposure risk
For workplaces and larger estates especially, waiting for the “perfect” season is rarely practical. The exception to this advice is for schools, where buildings are not under normal occupation during the summer months over the long school holidays, so summer testing is not advisable in education settings and best planned for the Autumn term.
Hot Weather Can Change Building Behaviour in Unexpected Ways
Interestingly, warmer weather doesn’t always reduce radon uniformly.
Factors such as:
- air conditioning
- mechanical ventilation systems
- building airtightness
- basement use
- overnight ventilation habits
can all influence how radon behaves indoors.
Every building responds differently. That’s why professional interpretation and correct detector placement remain important, particularly in complex properties or multi-site estates.
What This Means for Homeowners and Employers
The recent hot weather is a useful reminder that indoor environments are constantly changing. Ventilation, occupancy and building use all affect air quality, including radon concentrations.
The key takeaway is simple, don’t avoid testing because it’s summer.
Instead, ensure testing is:
- long enough
- properly interpreted
- and carried out using the correct methodology
A Long-Term Approach Gives the Clearest Picture
When it comes to radon, one isolated reading rarely tells the full story.
Longer-term testing provides a far more representative understanding of how a building performs across changing conditions, including periods of extreme weather.
Thinking About Testing This Summer?
Whether you’re managing a home, workplace or large property portfolio, understanding radon risk starts with reliable measurement.
Because when it comes to radon, it’s about understanding the environment inside.
For more information contact our radon specialists today!
