Radon (Rn): The Invisible Gas Killing 3,300 Canadians a Year

Radon is a radioactive gas. It has no colour, no smell, and no taste. Right now, it may be accumulating in the basement of your Ottawa or Gatineau home, and you would have absolutely no way of knowing without a test. Radon is the leading cause of lung cancer in non-smokers in Canada, responsible for more than 3,300 deaths annually according to Health Canada. It is not a remote or theoretical risk; it is a measured, documented reality in a significant percentage of Canadian homes. The first step toward addressing it, and integrating radon awareness into your overall indoor air quality strategy, is understanding exactly what it is and where it comes from.

 

What Is Radon, Exactly?

Radon is a naturally occurring radioactive gas produced by the breakdown of uranium in soil, rock, and groundwater. It forms continuously in the ground beneath and around your home. Outdoors, it disperses harmlessly into the atmosphere at concentrations too low to cause harm. The problem begins when radon seeps into enclosed spaces.

When radon is released indoors, it has nowhere to go. It accumulates, particularly in basements, crawl spaces, and lower floors. As radon continues to decay, it produces radioactive particles called radon progeny. When inhaled, these particles embed in lung tissue and release bursts of radiation that can damage DNA and, over years of exposure, trigger lung cancer. There is no threshold below which radon is considered completely safe. Health Canada explicitly states that there is no safe level of radon exposure.

 

How Radon Enters Canadian Homes

Understanding the entry points helps Canadian homeowners recognize their own risk. Radon is a gas, and it follows air pressure. Most Canadian homes are under slightly negative pressure relative to the soil beneath them, which means air, and anything dissolved in that air, is continuously drawn upward into the living space.

The most common entry pathways documented by Ottawa Public Health and Health Canada include:

• Cracks in poured concrete foundation floors and walls
• Gaps around service pipes and utility entries where they penetrate the foundation
• Sump pump pits and floor drains that connect to the soil below
• Hollow-block foundation walls, which provide a direct pathway from soil to interior
• Exposed soil floors in crawl spaces

Older Ottawa-area homes with original fieldstone or block foundations are particularly susceptible. New construction is not immune; the December 2025 update to the National Building Code now requires newly built Canadian homes to include a passive radon stack to help reduce indoor radon buildup, but that measure still requires provincial adoption to become mandatory across the country.

 

Canada’s Radon Guideline: 200 Bq/m3 and the Push to Lower It

Health Canada’s current guideline recommends taking corrective action when indoor radon levels exceed 200 becquerels per cubic metre (Bq/m3). For context, outdoor radon concentrations in Canada typically range from 10 to 40 Bq/m3. A reading of 200 Bq/m3 indoors represents a concentration five to twenty times higher than you are breathing outside.

As of March 2026, researchers cited in CBC News are actively pushing Health Canada to lower this threshold, arguing that the current guideline leaves too many Canadians at elevated risk. A homeowner whose Ottawa home tested at 114 Bq/m3 described in the same CBC report being technically within the guideline while still breathing air with radon levels more than double the outdoor baseline. The science is moving, and the precautionary message from researchers is now consistent: reduce your radon levels as much as practically possible, regardless of whether you are above or below the official threshold.

 

Who Is at Greatest Risk?

Radon risk accumulates with time and concentration. The following factors increase your household’s total exposure:

• Homes with lower floors used as living spaces, bedrooms, or home offices. Radon concentrates in the lowest levels of a building.
• Homes in regions with uranium-rich soil geology, which includes parts of Ontario, Quebec, Manitoba, and Saskatchewan.
• Occupants who spend significant time on lower floors, including children and anyone who works from home.
• Smokers or former smokers. The combination of radon exposure and tobacco smoke dramatically multiplies lung cancer risk, far beyond either risk factor alone.
• Homes with poor ventilation. A tightly sealed, energy-efficient house that holds heat well in Ottawa winters also holds radon well. The same sealed envelope that reduces heating costs can significantly increase radon concentration.

 

Testing: The Only Way to Know

Radon cannot be detected by sight, smell, or any sensory cue. Testing is the only answer. Health Canada recommends every home be tested, regardless of location, building type, or whether a mitigation system is already in place. Radon levels vary widely between homes on the same street, and even between units in the same building.

Two primary testing approaches exist. Short-term tests using charcoal canisters take 2 to 7 days and give a quick snapshot, but Health Canada notes that readings can vary significantly with weather, season, and ventilation habits. Long-term tests using alpha track detectors run for a minimum of 91 days, ideally across a winter heating season when windows are closed and radon levels are typically at their peak. The long-term test gives a more representative annual average and is the basis for making mitigation decisions.

The Canadian National Radon Proficiency Program (C-NRPP) maintains a directory of certified radon testing and mitigation professionals across the country.

 

What Mitigation Actually Looks Like

If your test returns a result above 200 Bq/m3, a certified radon mitigation professional will assess the options. The most effective and widely used system is sub-slab depressurization: a pipe is installed through the foundation floor slab, and a continuously running fan draws radon gas from beneath the slab and vents it safely outside before it can accumulate indoors. Properly installed, these systems routinely reduce indoor radon levels to near-outdoor concentrations.

Other measures include sealing visible cracks and gaps in the foundation, improving basement ventilation, and installing a heat recovery ventilator (HRV) to increase fresh air exchange without sacrificing heating efficiency.

 

Radon and Your HVAC System

 

What Homeowners Often Assume	What Field Experience Shows
My newer home doesn’t have a radon problem.	Construction era does not determine radon levels. Soil geology beneath the home is the primary driver. Modern homes can test very high; older homes can test low. Testing is the only answer.
I sealed my foundation cracks, so I’m protected.	Sealing cracks reduces entry pathways but cannot eliminate radon intrusion completely. Sub-slab depressurization is required when levels exceed the guideline.
My HVAC system recirculates the radon out of my basement.	A forced-air HVAC system running recirculation mode redistributes radon throughout the entire home. Without fresh air introduction from an HRV or dedicated ventilation, recirculation moves the problem upstairs.
Testing once is sufficient.	Health Canada recommends re-testing after any mitigation, after major renovations, and periodically over time. Radon levels change with soil conditions and home modifications.

 

Radon is one piece of a broader indoor air quality picture. A professionally cleaned duct system that moves fresh, filtered air efficiently throughout your home is a meaningful complementary measure, particularly when combined with HRV integration. To understand how duct cleaning supports better indoor air quality in your specific home, or to get a quote from 1 Clean Air’s NADCA-certified team serving Ottawa, Gatineau, Kingston, and Montreal, book online or call 613-612-4828.