How Seasonal Changes in Toronto Impact Indoor Air Quality and Radon Levels

Posted in Air Quality, on March 11, 2025

Seasonal changes bring about all kinds of adjustments to air quality, both indoors and out. Many of these changes can be detected during air quality testing in Toronto, from increased pollen, other allergens, or pollutants. During an environmental assessment, the SafeAir team also looks at temperature, humidity, and other environmental factors that may have a bearing on mold growth, airflow, and pollutant buildup. Whether you’re looking for an air quality test or radon testing this spring, here are some of the year-round shifts that our team notices.

How Different Seasons Affect Indoor Air Quality in Toronto

Winter

Winter can be one of the most challenging seasons for your home’s indoor air quality. Windows and doors remain tightly shut to conserve heating, which reduces the need for ventilation and airflow. This reduction can lead to a greater buildup of allergens like dust or pet dander, as well as radon gas accumulation. Humidity levels indoors tend to drop in the winter when colder air holds less moisture, and this can lead to more significant respiratory irritation as nasal passages dry out.

Spring

As the mercury starts rising, so do plants and molds: springtime air quality testing almost always shows an increase in pollen and spores! Melting water and emergent leaks or winter damage to the roof can also result in moisture buildup, which increases your risk of mold growth. As the temperatures fluctuate up and down and the ground thaws, some homes may also experience a shift in radon levels. 

Summer

Hello, summer! Southern Ontario has wonderful bright, hot, and humid summers — all this humidity may feel good for our skin, but it can also get trapped in homes, creating the ideal environment for both dust mites and mold spores. When the air conditioning gets turned on to combat the humidity, recirculated indoor air can trap pollutants or allergens indoors, providing little relief. 

Fall

As the summer winds down, autumn is a season of decay and change. A new crop of allergens and pollutants appears as the leaves fall, and increased moisture from rainfall can increase your risk of mold. As the house gets sealed against the cold, fresh air is, once again, curtailed, limited needed ventilation. 

Seasonal Changes and Radon Levels in Toronto

What is Radon and Why is it a Concern?

Radon gas is a colourless, odourless, invisible gas created by uranium deep within the earth’s surface. It’s very common across Toronto and the GTA, where it slips into people’s homes, usually through the basement or lower levels. Long-term radon exposure is the second-most leading cause of lung cancer in Canadians, which is why having your home tests for radon gas is essential. 

Why Radon Levels Change with the Seasons

The flow of radon gas is hard to guess at or determine; the only way to know if your home is affected is to have radon testing done. Radon levels will often fluctuate with the seasons. In the winter, sealed homes and reduced indoor airflow will often cause an uptick in tests. In the spring and fall, the changes in temperature and air pressure can pull more radon into your house, while in the summer months, many homes will naturally test lower because of increased ventilation. 

How to Improve Indoor Air Quality and Reduce Radon Risks

Improving your home’s indoor air quality begins with comprehensive indoor air quality testing in Toronto. SafeAir can help you understand your home’s unique air environment and what kinds of issues may be increasing your exposure to common air quality pollutants. 

There’s no ideal season for air quality testing — as you can see, seasonal shifts make air quality a moving target. Three things we recommend all our clients do are:

1. Increase or decrease ventilation based on the season. Open windows and doors and use air purifiers to help move and refresh air. 
2. Control your indoor humidity level by balancing it at 50%. This may require the use of a dehumidifier or humidifier, depending on the season!
3. Regularly maintain your HVAC and air filter system to reduce allergens and pollutants. 

If you haven’t had your home tested for radon yet, we suggest you add that to the list, too — a long-term test that bridges two seasons can help you understand your home’s risks and even out any shifts due to weather. 

Toronto’s seasonal changes affect air quality and radon exposure all year round. Proactively protect your home with SafeAir: Call or email our team to book indoor air quality testing in Toronto or learn more about radon testing today. 

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