What does my radon result mean, and was the test long enough?

This tool compares your long-term average with Canada’s guideline of 200 Bq/m³, the level at which Health Canada recommends corrective action. It also checks whether your test ran 91 days or longer and whether at least 91 of those days fell in the heating season. It cannot measure the radon in your home; only a test can do that. It makes no prediction about your health. It tells you how your number compares with Canadian guidance and whether your test met the conditions.

See what 200 Bq/m³ means and how soon to act.

Compare the long-term average, not a daily spike, with the guideline

The guideline applies to the average level over a year, not to one hourly, daily or short-term reading. Radon rises and falls with the weather, ventilation, heating and the state of the building. A monitor can show readings above 200 Bq/m³ on some days when the long-term average is below it. Base the decision on the longest and most representative average you have. The tool takes a result in Bq/m³ or pCi/L and converts a pCi/L reading by multiplying it by 37.

Convert a pCi/L reading to Bq/m³ yourself.

A test shorter than the minimum cannot settle a decision to fix

A test under 91 days is shorter than the minimum and may not estimate the annual average. Health Canada counts a test of 91 days or longer as long-term and anything under 91 days as short-term. It recommends a test of 3 to 12 months. The tool reports that result as one that cannot be judged against the guideline and recommends a new long-term test. It gives no instruction to fix the home on a short test.

Find out how to run a long-term test.

A test that missed the heating season may read low, so a low result needs a retest

Health Canada’s guide calls for at least 91 days of the test in the heating season. A test of 91 days or longer with fewer than 91 heating-season days is valid for the period it covered. It may still underestimate the annual average. If that result is below 200 Bq/m³, the tool recommends a retest in the next heating season. If a test of 91 days or longer reads above 200, no retest is needed before acting. A test with 91 or more heating-season days meets the minimum.

Check whether your test needs repeating.

A result near the guideline could sit on either side of it

Repeated results may vary by plus or minus 25% under the CSA and ANSI standards Health Canada cites. A result slightly below 200 Bq/m³ could truly be over, and one slightly above could truly be under. The tool flags any result from about 150 to about 250 Bq/m³ as possibly on either side.

No level is risk free. Any reduction in exposure reduces risk, and 200 is where Health Canada recommends corrective action. For a separate reference, the World Health Organization recommends a national reference level of 100 Bq/m³. The WHO says no more than 300 where 100 cannot be reached.

Read the questions people ask about a result near 200.

Above the guideline, Health Canada recommends fixing the home and says how soon

When a test of 91 days or longer reads above 200 Bq/m³, Health Canada recommends corrective action within one year, and sooner as the level rises. That applies at any time of year. Health Canada publishes no separate deadline for any higher level. The higher the level, the faster the action it calls for.

The tool reports two bands and nothing else. At or below 200, it says no level is risk free, keep the result, and the retest rules apply. Above 200 on a valid long-term test, it says Health Canada recommends corrective action within one year, sooner the higher the level.

See how a high level is fixed.

How to work it out by hand

The tool applies Health Canada’s rules to your number in a fixed order. You can follow the same steps with a pen.

1. If your result is in pCi/L, multiply it by 37 to get Bq/m³.
2. Check that the test ran 91 days or longer. Under 91 days, the result cannot be judged against the guideline, and a new long-term test is the next step.
3. Check that 91 or more of those days fell in the heating season. If not, and the result is below 200 Bq/m³, plan a retest in the next heating season.
4. Compare the result with 200 Bq/m³.
5. If the result is within about 25% of 200, from about 150 to about 250 Bq/m³, treat it as possibly on either side of the guideline.
6. Above 200 on a test that passed step 2, Health Canada recommends corrective action within one year, sooner the higher the level. Too few heating-season days does not change this.

Health Canada’s measurement guide names four conditions that qualify a result. Check your test against each one.

• The test ran under 91 days.
• The device was tampered with or damaged.
• Fewer than 91 days fell in the heating season.
• The detector was placed other than as the guide directs.

See how the Index checks its numbers and dates.