Short answer
Radon becomes a concern when the long-term average in a lived-in part of your home is above Health Canada’s 200 Bq/m³ guideline. Health Canada recommends reducing it within two years for 200–600 Bq/m³ and within one year above 600. Risk grows with both the level and the years of exposure, so basement bedrooms, smokers and young families matter most. There is no known completely safe level.
Key facts
- Action level: 200 Bq/m³ long-term average (Health Canada).
- 200–600 Bq/m³: fix within 2 years. Over 600: within 1 year.
- Exposure = concentration × time spent there.
- Highest priority: basement bedrooms, smokers and former smokers, children.
The levels that matter
| Long-term average | What Health Canada recommends |
|---|---|
| Under 100 Bq/m³ | Below Canada’s guideline and the WHO reference level. No action needed. |
| 100–199 Bq/m³ | Below the guideline. Optional reduction: there’s no known safe level, and Health Canada encourages keeping levels as low as reasonably achievable. |
| 200–600 Bq/m³ | Above the guideline. Reduce within 2 years. |
| Over 600 Bq/m³ | Well above the guideline. Reduce within 1 year. |
These timelines apply to long-term results, averaged over at least three months. A single high reading from a few days of testing isn’t enough to act on, though a very high short-term result is a good reason to start a long-term test right away.
Time matters as much as concentration
Radon’s harm comes from cumulative exposure over years. A useful way to think about it is level × time. Two hundred becquerels in a room you visit for ten minutes a day is a small dose. The same level in a room where someone sleeps eight hours a night is a meaningful one. That’s why the guideline focuses on the “normal occupancy area”: anywhere someone spends more than four hours a day.
Rooms that deserve the most attention
- Basement bedrooms and guest rooms, where people spend long hours at the highest radon level in the house.
- Basement apartments and secondary units, which are often the lowest, highest-radon space and someone’s whole home.
- Home offices and family rooms on the lowest floor.
- Slab-on-grade bungalows, where the main living space sits directly on the ground.
People with the highest risk
- Current and former smokers. Radon and smoking multiply each other’s effects.
- Children and young families, because they have the most years of future exposure ahead. Risk by age.
- People who spend most of the day at home: retirees, remote workers, caregivers. Checklist for older adults.
When during the year radon is highest
Levels usually peak in the heating season, when the stack effect is strongest and windows are closed. That’s the best time to test, and also when exposure is greatest. Summer readings are often lower and can make a home look better than it is over a full year.
Should I do anything while I wait for results?
Unless you have reason to think levels are extreme, normal life is fine during a 91-day test; in fact, the test needs normal conditions to be accurate. If a screening test or an early reading came back very high (several hundred Bq/m³ or more), reasonable short-term steps include spending less time on the lowest level, keeping the sump covered, and not smoking indoors, while you arrange a proper test and assessment.
Common questions
What radon level is considered dangerous in Canada?
Health Canada recommends action when the long-term average exceeds 200 Bq/m³ in an area where someone spends more than four hours a day. Higher levels call for faster action: within 1 year above 600 Bq/m³.
Is 150 Bq/m³ safe?
It’s below Canada’s guideline, so no action is required. It is above the WHO reference level of 100 Bq/m³, and because risk rises steadily with exposure, some families choose to mitigate at this level.
Is it safe to sleep in a basement with radon?
If a long-term test shows the basement is below 200 Bq/m³, Health Canada considers no action necessary. If it’s above, the bedroom is exactly the kind of space the guideline is designed to protect, and mitigation is recommended.