How to test your home for radon: common questions

Radon is a radioactive gas from the ground, and it can get in anywhere your home touches the soil.

Health Canada explains that radon forms when uranium in soil and rock breaks down. You cannot see or smell it, but radon test devices detect it easily. Outdoors it thins out to levels that are not a concern, but indoors it can build up.

Soil gas is the largest source of indoor radon. Common entry points are construction joints, gaps around pipes, support posts, floor drains, sumps, and cracks in foundation walls and floor slabs. Radon also moves through the foundation itself. Levels are usually highest in basements and crawl spaces, but high radon can turn up anywhere in a home.

See what radon is and where it comes from

Yes.

Health Canada recommends testing every home, no matter where it is or what type of building it is. It says to test in a normal occupancy area on the lowest lived-in level of the home. A normal occupancy area is a space where someone spends more than four hours a day, so a basement you live in counts.

See where to place your test in your home

Yes.

Health Canada says homes without basements can still have high radon. Levels can vary a lot between homes, even between nearby homes or units in the same building. Health Canada recommends testing on the lowest lived-in level, in a room where someone spends more than four hours a day.

See where to place your test in your home

Yes.

Health Canada says radon can occur in apartments, condos and other multi-unit buildings. Its guidance is that homes with no lived-in level touching the ground should still be tested. These homes usually have lower radon levels, but they can still be above the guideline.

If you are testing a whole building or several units, Health Canada's guide for public buildings applies instead. Its testing steps are different from those for a single home.

See how radon testing works in rentals and condos

Health Canada recommends testing for 3 to 12 months.

At least 91 days of the test must fall in the heating season. Indoor radon is usually higher in colder months, so a heating season test generally gives a conservative estimate of your yearly level. A test with fewer than 91 heating season days may underestimate your yearly average and may need to be redone.

Do not change how you live while the test runs. The aim is a result that matches your home's real conditions.

See how to run a long-term test

Not for deciding whether to mitigate.

Health Canada defines a short-term test as anything under 91 days, and a long-term test as at least 91 days. It states that short-term results are not suitable for deciding on mitigation.

Short-term tests do have a use. Health Canada says they can check how a mitigation system is working right after it is turned on. They do not replace a long-term test.

See how to run a long-term test

It depends on your result.

If your result was below 200 Bq/m³, retest so that at least 91 days fall in the next heating season. Health Canada says a test that runs partly or fully outside the heating season may underestimate your yearly average.

If your result was above 200 Bq/m³, you do not need to retest. Health Canada recommends that you take action to lower the radon level.

See whether you need to test again

Not necessarily.

Radon levels naturally rise and fall, so short spikes above 200 Bq/m³ are normal. Health Canada's guideline applies to the average yearly radon level. An hourly or daily reading cannot tell you that average.

Base your decision on the longest, most representative average you have. Health Canada says that is ideally a full 12-month measurement, or at least a long-term test of 91 days or more. You may need more testing if fewer than 91 days fell in the heating season.

See how radon monitors and test kits differ

Convert it to Bq/m³.

Health Canada states that 37 Bq/m³ equals 1 pCi/L, so multiply your pCi/L result by 37. Then compare it with Canada's guideline of 200 Bq/m³. A reading of 4 pCi/L, the United States action level, works out to 148 Bq/m³. That is below Canada's guideline but above the World Health Organization reference level of 100 Bq/m³.

Devices sold in the United States often report in pCi/L by default. Before you start the test, check whether yours can switch to Bq/m³, and check that C-NRPP lists it.

See your result converted to Bq/m³

Check that it has passed C-NRPP performance testing. Health Canada strongly recommends testing only with devices that have.

C-NRPP publishes separate lists for consumer electronic radon monitors and for professional devices and passive detectors. On the consumer list, monitors are "listed", and those graded A or B are "recommended". Some devices appear on neither list, usually because they are still in testing or under review.

Devices that fail the minimum performance requirements are recalled and appear in the Government of Canada's Recalls and Safety Alerts database. Health Canada also recommends thinking about replacing an electronic monitor five years after you buy it, unless it can be recalibrated to the maker's specifications. Many consumer monitors cannot be recalibrated at all.

See whether your device has passed testing

Yes, but it is rarely the main problem.

Groundwater can hold dissolved radon, and some of it moves into indoor air when you shower, do laundry or cook. Health Canada says this is a possible source for homes on a private well.

According to Health Canada, radon from water usually affects indoor levels less than radon from soil gas. Test indoor air and fix soil gas before dealing with water. Health Canada also says the health risk comes from breathing the gas, not drinking the water.

Canada has no maximum limit for radon in drinking water, and Health Canada says one is not needed. It says testing indoor air is the right way to assess your exposure, because it captures radon from all sources at once.

See why radon is common in Canada, including in homes on rural wells