A note before you read. This article is general information for Canadian homeowners — not medical, legal, or financial advice. Radon results are reported against Health Canada's guideline of 200 Bq/m³. RadonTest.ca coordinates kit logistics and sample submission only; we do not interpret your results or assess your health. All analysis is performed independently by a C-NRPP-certified laboratory.
Quick answer
Radon is a naturally occurring radioactive gas produced underground as uranium in soil and rock breaks down. It is colourless, odourless and tasteless, it seeps into buildings from the ground, and it is measured in becquerels per cubic metre (Bq/m³). Health Canada's guideline is 200 Bq/m³ as an annual average. Because you cannot sense it, the only way to know your home's level is a long-term test of at least 91 days.
This article is the definition: what radon is, where it comes from and how it behaves. If you would rather start with what to do about it in your own house, the radon in your home guide covers that end to end.
What radon actually is
Radon is a gas, and it is radioactive. Both halves matter.
Being a gas is why it moves. It is not locked into the rock it came from — it works its way up through soil, along cracks, and into whatever sits above, which in a Canadian winter is very often a heated house.
Being radioactive is why it matters to health. Radon atoms decay, and so do the short-lived products they turn into. When those decay products are breathed in, they can deposit in lung tissue. That is the mechanism behind every health statement further down this page — nothing to do with smell, air quality as most people picture it, or how clean a house looks.
Radon is chemically inert, which is a large part of why it travels so freely. It does not react with the soil it passes through, it does not get filtered out on the way, and it does not announce itself.
Where radon comes from
Radon is produced by the decay of uranium, which is present in small quantities in soil and rock nearly everywhere in Canada. That is the important part: radon is not a contaminant somebody introduced. It is a normal product of ordinary ground.
How much a given property produces depends on the local geology — what the ground is made of, how permeable it is, how water moves through it. This is why radon varies so much across the country, and why two houses on the same street can differ.
What radon is not is a function of how new, clean, expensive or well built a house is. Newer, tighter homes can hold radon more effectively than draughty older ones, which sometimes surprises people.
How radon gets into a house
A house is usually slightly lower in pressure than the ground beneath it, particularly in winter when warm air rises and escapes at the top. That difference draws soil gas in through any opening in contact with the ground:
- Cracks in a slab or foundation wall
- The gap where a floor meets a wall
- Sump pits, floor drains and other service openings
- Gaps around pipes and conduits
- Crawl space floors, especially bare earth
- Construction joints and utility penetrations
The result is that radon concentrates on the lowest lived-in level — the basement in most Canadian homes — and thins out as it disperses upward. That is why a test belongs on the lowest level you actually use.
Why radon matters
Health Canada identifies radon as the leading cause of lung cancer in people who do not smoke, and the second leading cause overall after smoking. Risk builds with two things together: how high the concentration is and how long the exposure lasts. It is a slope, not a switch — the risk does not appear at one number and vanish below it.
That is also why nobody describes a particular reading as risk-free. Below 200 Bq/m³ the guidance is that no action is recommended, which is not the same statement. For what the numbers mean in practice, see acceptable radon levels in Canada and, on the health side, is radon a lung cancer risk.
Radon and smoking together are worse than either alone — the risks multiply rather than add.
Invisible and odourless — so how do you know?
You measure it. There is no sensory cue at any concentration, and there is no way to infer a home's level from the neighbourhood, the age of the house or how it feels. People sometimes ask whether a carbon monoxide alarm will pick it up; it will not — it is built for a different gas entirely.
Two things make a Canadian radon measurement meaningful:
| Requirement | Why |
|---|---|
| At least 91 days | Radon swings day to day and season to season. A long test averages that out; a two-day snapshot mostly measures the weather. |
| Lowest lived-in level | That is where concentrations are highest and where the guideline is written to apply. |
Health Canada's guideline is an annual average, which is the reason short tests are not used to make decisions about a home. Placement matters too — the detector needs clear air, away from drafts and vents. Where to place a radon test kit covers the specifics.
If your result comes back above the guideline, radon can typically be reduced by more than 80% with a system installed by a C-NRPP-certified professional, usually in less than a day.
FAQ
What is radon, in simple terms? A radioactive gas that forms naturally underground as uranium in soil and rock breaks down. It is invisible, odourless and tasteless, and it enters buildings from the ground below them.
Where does radon in a house come from? The soil and rock underneath it. Radon moves up through the ground and is drawn in through cracks, joints, sump pits and service openings, because the house is usually at slightly lower pressure than the ground.
Is radon a concern? Health Canada identifies it as the leading cause of lung cancer among people who do not smoke. Risk rises with both concentration and years of exposure, so it is treated as a matter of measuring and, where the number is high, reducing it.
Can you see or smell radon? No. It is colourless, odourless and tasteless at every concentration. Measurement is the only way to know.
How do I find out whether my home has radon? Every Canadian home has some. What you need is the number, which means a long-term test of at least 91 days on the lowest lived-in level.
Is a level below 200 Bq/m³ risk-free? No level is described as risk-free. Below 200 Bq/m³ Health Canada recommends no action; lower is still better, because risk declines with concentration rather than disappearing at a line.
Is radon only a problem in certain regions? No. Geology shifts the odds, but radon has been found above the guideline in every province and territory, and neighbouring homes can differ substantially. Regional data tells you the odds; only a test tells you your house.
Sources
- Health Canada — Radon: https://www.canada.ca/en/health-canada/services/health-risks-safety/radiation/radon.html
- Health Canada — Radon: What you need to know: https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/radon-what-you-need-to-know.html
- Health Canada — Guide for radon measurements in residential dwellings: https://www.canada.ca/en/health-canada/services/publications/health-risks-safety/guide-radon-measurements-residential-dwellings.html
- Health Canada — Reducing radon levels in your home: https://www.canada.ca/en/health-canada/services/health-risks-safety/radiation/radon/reducing-levels-home.html
- Canadian National Radon Proficiency Program (C-NRPP) — Find a professional: https://c-nrpp.ca/find-a-professional/
Ready to find out your home's number?
A long-term test is the only way to move from "every home has some radon" to knowing what yours is. Our kit includes the detector, prepaid lab analysis at a C-NRPP-certified Canadian laboratory, return shipping and your Certificate of Analysis — plus the reminders that get the test finished and returned on time.