Short answer
Health Canada recommends action at 200 Bq/m³ (5.4 pCi/L). The U.S. EPA’s action level is 148 Bq/m³ (4 pCi/L), and it suggests considering a fix from 2 pCi/L up. The World Health Organization prefers a reference level of 100 Bq/m³ (2.7 pCi/L) and says it shouldn’t exceed 300. A result between 100 and 200 is under Canada’s guideline but above the WHO’s, and none of these numbers marks a safe level.
Key facts
- Health Canada: 200 Bq/m³ (5.4 pCi/L), reduce within 2 years, or 1 year above 600.
- U.S. EPA: 148 Bq/m³ (4 pCi/L) action level, and consider fixing between 2 and 4 pCi/L.
- WHO: 100 Bq/m³ (2.7 pCi/L) preferred reference level, not to exceed 300 Bq/m³.
- These are policy lines drawn on a risk that rises steadily, with no known safe threshold.
The three numbers side by side
| Body | Level | pCi/L | What it is |
|---|---|---|---|
| Health Canada | 200 Bq/m³ | 5.4 | Action level for a long-term average, in force since 2007. Keep levels as low as reasonably achievable. |
| U.S. EPA | 148 Bq/m³ | 4.0 | Action level. The EPA also recommends considering a fix between 2 and 4 pCi/L (about 74 to 148 Bq/m³). |
| World Health Organization | 100 Bq/m³ | 2.7 | Preferred reference level. Where that isn’t achievable, it should not exceed 300 Bq/m³ (8.1 pCi/L). |
To switch units, multiply pCi/L by 37 to get Bq/m³.
Why the numbers differ
All three bodies agree that radon causes lung cancer and that risk rises with exposure, with no known level at which it reaches zero. The numbers differ because each one is a policy line, and where a country draws it depends on more than risk. The WHO’s handbook treats its 100 Bq/m³ as the level to aim for and advises countries to weigh their own circumstances, including how many homes are tested and fixed. Canada set 200 in 2007 after lowering it from 800. How that change happened.
A line like this is a place to act. It isn’t a boundary between safe and unsafe. A home at 190 Bq/m³ carries a little less risk than one at 210, not a different kind of risk.
Which one applies to you in Ontario
Health Canada’s 200 Bq/m³ is the guideline for Canada, and it’s the one real estate practice and the new home warranty rely on. Tarion’s new home warranty, for example, covers radon remediation when a long-term test shows levels above 200 Bq/m³. That is the line the system uses. The EPA and the WHO figures are useful as benchmarks of what other health bodies recommend, and they’re a reasonable guide for your own decision.
If your result is between 100 and 200
This is the range where the three standards disagree, so it’s the range where people ask what to do. Under Canada’s guideline, no action is required. Above the WHO’s 100, and above the EPA’s “consider fixing” level, many families choose to act anyway. Reasons to lean toward it:
- Children. They have the most years ahead for damage to accumulate. Radon risk by age.
- A smoker or former smoker in the home. Radon and smoking multiply each other’s effects.
- A basement bedroom, suite or home office, where someone spends many hours at the highest-radon level.
- Radon damage can’t be undone, so each year you wait adds to the total. How radon damage works.
- The cost doesn’t change with the level. A system costs about the same at 150 as at 450. What it costs.
If you’d rather not mitigate, that’s within the guideline. Retest every few years and after renovations, since levels change with the house.
Make sure the number is a long-term number
All three standards are built on long-term averages. A result of 150 from a 48-hour kit says much less than a result of 150 from a 91-day test, so confirm it first. How to test.
Common questions
Why is Canada’s radon guideline higher than the U.S. and WHO levels?
Each is a policy line, not a safety boundary, and where it’s drawn depends on more than risk, including how many homes can realistically be tested and fixed. Canada’s 200 Bq/m³ was set in 2007. The U.S. EPA’s is about 148 Bq/m³, and the WHO’s preferred reference level is 100 Bq/m³.
Is 150 Bq/m³ a problem in Canada?
It’s below Health Canada’s 200 Bq/m³ guideline, so no action is required. It’s above the WHO’s 100 and slightly above the EPA’s 148, and because risk rises steadily with exposure, many families with children, smokers or a basement bedroom choose to mitigate.
Which radon standard should I follow?
In Ontario, Health Canada’s 200 Bq/m³ is the guideline that real estate practice and the new home warranty use. The EPA and WHO levels are helpful benchmarks if you want to go further.
How do I convert pCi/L to Bq/m³?
Multiply pCi/L by 37. 4 pCi/L is about 148 Bq/m³, and 5.4 pCi/L is about 200 Bq/m³.
Sources
- Health Canada — Government of Canada radon guideline
- U.S. EPA — Radon
- U.S. EPA — Does the 2009 World Health Organization recommendation to lower the radon action level affect EPA’s?
- World Health Organization — WHO Handbook on Indoor Radon (2009)
- Tarion — New home warranty coverage
- Health Canada — Guide for Radon Measurements in Residential Dwellings (Homes)