If you have ever wondered why radon experts recommend testing during the colder months, the answer lies in how a Calgary home behaves in winter. Radon levels are not constant throughout the year — they tend to climb significantly during the heating season. Understanding why helps you test at the right time and appreciate why winter is when your family's exposure is often highest.
First, the source never stops. Radon is continuously produced as uranium in Alberta's soils decays, and it is always seeking a path upward. What changes seasonally is not the amount of radon in the ground but how much of it ends up inside your home. Several winter factors combine to pull more soil gas indoors and trap it there.
The biggest driver is the stack effect. When the air inside your home is much warmer than the bitterly cold air outside, that warm air rises and escapes through the upper levels of the house — around attic hatches, light fixtures, and the top of the building envelope. As warm air leaves the top, it creates a slight negative pressure lower down, and the home draws replacement air in from wherever it can find it.
Unfortunately, one of the places it draws from is the soil beneath your foundation. The home essentially acts like a chimney, and the negative pressure at the basement level actively sucks radon-laden soil gas up through cracks, joints, sump pits, and pipe penetrations. The colder it is outside, the stronger this effect becomes — and Calgary winters are very cold.
In summer, open windows and doors let radon dilute and disperse. In a Calgary winter, the opposite happens. We keep everything shut to hold in heat, dramatically reducing natural ventilation. Radon that enters has far fewer paths to escape, so concentrations build up indoors over the months we are sealed in.
There is a third factor. When the ground around your foundation freezes and is capped with snow, the soil's surface is effectively sealed. Radon that would normally vent harmlessly up through open earth around the house is instead diverted toward the one remaining easy exit: the relatively warm, lower-pressure space beneath your home. More of the available radon gets funnelled indoors.
Running furnaces, along with exhaust fans, range hoods, and clothes dryers, can add to indoor depressurization. Each one pushes air out of the house, and that air has to be replaced — again, partly by soil gas drawn up from below. In an airtight winter home, these everyday appliances quietly increase radon entry.
Because winter is when radon is typically highest, it is also the most informative time to measure. A test conducted during the heating season captures your home closer to its peak exposure, giving you a more protective, conservative read. This is why Health Canada recommends long-term testing of at least 90 days, ideally during the cooler months.
A test run only in summer with windows open can substantially underestimate your true winter exposure. If your previous testing was warm-weather only, a heating-season test is well worth doing.
The practical takeaway is straightforward: the months when your family spends the most time indoors are often the months with the highest radon. That overlap is exactly why winter exposure deserves attention rather than being dismissed as a seasonal quirk.
Winter does not create radon, but Calgary winters concentrate it indoors through the stack effect, sealed-up homes, frozen ground, and hardworking furnaces. Test during the heating season for the most accurate picture, and if your levels are elevated, a mitigation system works year-round to keep them low. Onyx Radon's C-NRPP certified team can measure your winter levels and deliver rock-solid protection that does not take the season off.
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