Radon levels can be measured using several different technologies. Although there are pros and cons to specific kinds of test types, the most important thing to do is to test a building for a long period of time (~3 months or more).

The amount of radon entering a building can fluctuate up and down quite a lot over a short period of time. From day to day, or even from hour to hour, radon can be very high or very low. This is normal and is influenced by many factors, such as how your home ‘breathes’ outside air, furnace use, the weather and even geologic phenomena. By having a long (90+ days or more) radon test, these fluctuates are averaged out, returning the real radon level of a property.

Radon is not static, it changes hour by hour as your home ‘breathes’

We ‘see’ radon fluctuate over time by using 250,000+ real time radon readings. Taking hourly measurements from >50 homes in Canada, we measured the yearly radon average. In the figure below, we will use this real world data to demonstrate the need for long term tests.

How to read this figure:

  • the vertical axis is how much radon can differ from the real radon level in given test period.
  • the horizontal axis is the “radon testing period” which are increasingly longer duration radon tests. The shortest test is taken hourly, while the longest test is taken over 180 days.  


Real time radon readings from over 50 properties across Canada demonstrating that short term tests (hourly to 60 days) can have a significantly different radon reading from the actual residential radon level. 

What does it mean?

If you are just looking at radon in a one hour ‘snap shot’ it can vary up to 1000 Bq/m3 from a properties’ actual average. This is an incredible fluctuation. But if the radon test is lengthened to 90+ days, the measured radon level is the best representation of the real radon level.

Consequently, a result of these normal fluctuations is that measuring radon over a short period (hours or days) will often give a false reading compared to what is the average for a long period (several months). This false reading can be a false positive or a false negative, meaning you might think you have a problem when you don’t, or (worse) you think you’re safe when you are not.

A precise radon test (that gives you a reading = actual amount of radon you are being exposed to over the long term) requires a measurement taken over several months ideally 3 or more.

A study of 776 Canadian ‘closed house’ short (5 day) and long (90+ day) radon tests showed that long term testing was precise >96% of the time. In contrast, short term testing was “wrong” (meaning the short term test failed to predict the long term test outcome) 20-98% of the time depending on season.

Reference: Stanley et al. Radon exposure is rising steadily within the modern North American residential environment, and is increasingly uniform across seasons. 2019, Scientific Reports, 9 (18472)

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