Radon in Ottawa homes: how to test properly (long-term, heating season) and what the numbers mean

Updated 2026-09-16

Health Canada's radon guideline, what the Ottawa data shows, how to run a long-term test in the heating season, and when a C-NRPP professional is worth it.

What radon is and the number that matters

Radon is a radioactive gas that comes from uranium breaking down in soil and rock. You cannot see it or smell it. It gets into houses through cracks, floor drains, sump pits and gaps around pipes, and it builds up in basements.

The Government of Canada guideline is 200 becquerels per cubic metre (Bq/m³). Health Canada's current guideline page says that if your home is above 200 Bq/m³, you should take action to lower it within one year, and sooner the higher the level. It also says no level is risk free, so a result under 200 is good news, not a guarantee.

What the Ottawa numbers show

Health Canada's Cross-Canada Survey tested 13,807 homes with three-month detectors during the fall and winter of 2009-10 and 2010-11. In the City of Ottawa health unit, 6.2% of the 64 homes tested were above 200 Bq/m³. Ontario as a whole came in at 8.2%, and 6.9% nationally.

Treat that Ottawa figure with care. Sixty-four homes is a small sample for a city this size. The more recent Evict Radon national study (Cross-Canada Radon Survey, University of Calgary), which tested a larger volunteer sample across the whole Ottawa–Gatineau metro area, reports about 1 in 6 properties at or above 200 Bq/m³. The two studies used different samples and areas, so read them as a range, not a contradiction. Ottawa Public Health says radon levels vary a great deal across Canada and within the City of Ottawa. Two houses on the same street can test very differently.

The only way to know your number is to test your own home.

How to run a proper test

Use a long-term test. Health Canada's measurement guide calls for at least 91 days, and 3 to 12 months gives a better average. Short tests of a few days swing too much with weather to base a repair decision on.

Test in the heating season. The guide asks that at least 91 days of the test fall during the heating season, when windows are shut and the house draws more soil gas. In Ottawa, starting in October or November works well.

Place it right. The detector goes on the lowest level where someone spends time, often a finished basement. Keep it at least 30 cm above the floor and 30 cm from walls, and at least 1 m from vents, windows and doors. Do not test in a kitchen, bathroom or laundry room.

Leave it alone for the full period. When it is done, seal it and mail it to the lab straight away, with the start and end dates filled in.

Test kit or C-NRPP professional

A do-it-yourself long-term kit is a sound choice for most homes. Ottawa Public Health says kits are sold online and at hardware and building supply stores, and lists prices from about $29 to $170. Follow the kit instructions exactly.

A professional makes sense if you are buying or selling, if you have a large or split-level house, or if you want the placement and paperwork done for you. Health Canada recommends using people certified by the Canadian National Radon Proficiency Program (C-NRPP). You can look them up at c-nrpp.ca. An indicative 2026 range for a professionally placed long-term test in Ottawa is about $150 to $300.

For a real estate deal with no time for a three-month test, a short test can flag a problem. It should be followed by a long-term test once you move in.

Reading your result

Under 200 Bq/m³: you are below the guideline. Some owners retest after big renovations, such as finishing a basement or replacing windows, since those can change airflow.

Over 200 Bq/m³: plan a fix within the year. Health Canada recommends a C-NRPP certified mitigation professional. Its Take Action on Radon program says most systems can be installed in less than a day and cut radon by more than 80% in most homes.

Well above 200: move faster. The guideline says the higher the level, the sooner you should act.

Keep the lab report. You will want it when you compare the retest after mitigation, and a buyer may ask to see it.

Common testing mistakes

Testing in summer. Open windows and less stack effect usually mean lower readings, so a summer result can look better than your real yearly average.

Putting the detector in the wrong place. A shelf in the furnace room, a spot beside the sump or a detector on the floor will not give a fair reading of the air you breathe.

Stopping early. A kit pulled after six weeks is no longer a long-term test. Mark the end date on your calendar when you start.

Waiting too long to mail it. Most kits ask you to send the detector to the lab right away once the test ends. Read the instructions on the day you open the package.

Relying on one short test from a home sale. Use it as a flag, then run a proper long-term test in your first heating season.