Canadian RadonServices Index
Menu

What does my radon result mean, and how soon do I have to act?

Safe radon levels in Canada: 200 Bq/m³ guideline, how soon to act, what 150, near 200 or 1,000 Bq/m³ means, and how Canada compares with WHO and the US.

An empty finished basement bedroom with a wood floor.

Photo: Famartin, CC BY-SA 4.0, cropped, via Wikimedia Commons.

Health Canada’s guideline is 200 Bq/m³. It applies to the average annual radon level in a normal occupancy area of the home. When a long-term test comes back above 200, Health Canada recommends fixing the home within one year, and sooner the higher the level is. Below 200, the guideline does not call for corrective action, but no level of radon is risk free. Enter your number and test length to see where your result sits.

Health Canada’s guideline is 200 Bq/m³, and no level is risk free

The guideline is the level at which Health Canada recommends corrective action. Health Canada does not call it a safe level. In its words, “the health risk below 200 Bq/m³ is small, but there is no level considered risk free.” Any reduction in exposure reduces risk.

Risk below the guideline

No risk-free level

Health Canada describes the health risk from radon below 200 Bq/m³ as small, with no level considered risk free. The guideline is the level at which corrective action is recommended, not a safe level, and any reduction in exposure reduces risk.

Date
2025-09-24
Sample
Not applicable
Source
Health Canada, Canadian Radon Guideline (updated 24 September 2025)
Copy citation

The guideline applies to the average level in a normal occupancy area. That is a part of the home where someone is likely to spend more than four hours a day.

  • Counts: a finished basement family room
  • Counts: a bedroom, office or playroom
  • Counts: a workshop or a basement apartment
  • Does not count: a crawl space or an unfinished basement
  • Does not count: a cold room, storage area, furnace room or laundry room
  • Does not count: any area normally closed off or rarely used

A space you use less than daily still counts if it averages more than four hours a day over a year. A basement studio used heavily on weekends is one example. See which level and room count as a normal occupancy area in your home.

Above 200 Bq/m³, fix it within a year, and sooner the higher it is

When a test of 91 days or longer comes back above 200 Bq/m³, Health Canada recommends corrective action within one year. The higher the level, the faster it says to act.

The goal is to reduce the level as much as is practicable, which means as low as standard methods can get it at a reasonable cost. In most situations a final level below 200 can readily be reached. The guideline is not a stopping point for mitigation if it is reasonable to go lower.

A result of 1,000 Bq/m³ is five times the guideline. Health Canada publishes no separate deadline for it; its advice is to act faster as the level rises. In a very small number of cases the level stays above 200 after all reasonable corrective action; those homes are managed case by case. See how a high level is fixed and what a system does.

Only a long-term average counts against the guideline

The guideline applies to the average annual radon level, not to a single hourly, daily or short-term reading. Radon rises and falls with weather, ventilation, heating and building conditions over hours, days and seasons. A monitor can show readings above 200 Bq/m³ on a day when the long-term average is below 200. Health Canada says to base decisions on the longest and most representative average you have.

See how to run a long-term test.

If a result below 200 came from a test with fewer than 91 days in the heating season, it may underestimate the annual average. Health Canada then recommends testing again in the next heating season. If a test of 91 days or longer is above 200, you do not need a retest before acting. Check whether your test needs repeating.

A result close to 200 could sit on either side of the line

Two tests of the same home can differ by a quarter and both be within the standard, so a result near 200 Bq/m³ can land on either side. That band means a result slightly below 200 Bq/m³ could truly be over, and one slightly above could truly be under.

The wording also differs between sources. The 2024 survey counts homes at or above 200, and Health Canada recommends action when the annual average exceeds 200. For a statistic that is a rounding error. For a home at exactly 200, the uncertainty band applies.

Risk changes gradually with exposure, about 16% per 100 Bq/m³ with no threshold, so 199 and 201 carry close to the same risk. Read the questions people ask about a result near 200.

Canada’s guideline is higher than the WHO reference level and the US action level

The World Health Organization recommends a national reference level of 100 Bq/m³. The United States sets its action level at 4 pCi/L, about 150 Bq/m³.

US EPA action level

4

pCi/L

Level at which the United States Environmental Protection Agency recommends fixing a home, about 148 Bq/m³ and commonly rounded to 150 Bq/m³ in its public information. The EPA also recommends considering action between 2 and 4 pCi/L.

Date
2026-09-18
Sample
Not applicable
Source
United States Environmental Protection Agency, Radon
Copy citation

One pCi/L is 37 Bq/m³, so 200 Bq/m³ is about 5.4 pCi/L and 150 is about 4.1 pCi/L. A long-term result of 150 Bq/m³ is below Canada’s guideline, so it does not trigger the recommendation for corrective action. It is above WHO’s reference level and close to the US action level, and it is not a risk-free level.

All three levels are public health decision points, not biological boundaries where radon suddenly becomes dangerous. WHO reports the same rise in risk per 100 Bq/m³. The 2024 survey counted how many Canadian properties sat at or above the WHO level. See how common high levels are by province.

To compare a US result with Canada’s guideline, convert pCi/L to Bq/m³ and back.

Sources

  1. 1. Health Canada, Canadian Radon Guideline (updated 24 September 2025)
  2. 2. Health Canada, Guide for radon measurements in homes (updated 22 May 2026)
  3. 3. World Health Organization, WHO Handbook on Indoor Radon: A Public Health Perspective, 2009
  4. 4. United States Environmental Protection Agency, Radon
  5. 5. Cross-Canada Radon Survey 2024 report, Version 1.1 (CCSR.24.1.1), October 2024