Radon Testing in GTA Homes: Short-Term vs Long-Term Tests and When to Retest

For a Toronto or GTA home, the best radon test is a long-term test of at least 91 days with a minimum of 91 days of it in the heating season, placed on the lowest lived-in level. A short-term test is a quick screen only. Professional radon testing turns the Health Canada guideline of 200 Bq/m³ into a result you can act on.

Radon is a radioactive gas that moves up from soil and rock and can collect in a basement or lower level. You cannot see, smell or taste it, so a measurement is the only way to know. The rest of this guide explains the two test types, where the detector goes, what the numbers mean and when to test again.

What is the difference between a short-term and a long-term radon test?

A long-term test runs for at least 91 days, while a short-term test is anything shorter. Radon levels in a house rise and fall with weather, wind, heating and how the home is used, so a few days of data can miss the typical level.

According to the Health Canada guide for radon measurements in residential dwellings, a long-term measurement spans at least 91 days, and at least 91 days of the test should fall in the heating season. Health Canada recommends testing over a period of 3 to 12 months. The same guide says short-term measurements are not appropriate for informing mitigation decisions.

Question	Short-term test	Long-term test
Length	Under 91 days	91 days or more, 3 to 12 months recommended
Best use	Quick screen, or a first look before buying or selling	The result you compare to the 200 Bq/m³ guideline
Should it drive a mitigation decision?	No, per Health Canada	Yes
Season	Any, but results swing more	At least 91 days in the heating season

What radon level should make me act?

Health Canada's guideline is 200 Bq/m³, and it applies to your average annual level. The guide says to take corrective action if the average annual level exceeds 200 Bq/m³, and it notes that measurements carry an uncertainty of up to 25 percent.

That is why the guideline is compared with a long-term average and not with a single weekend reading. If your long-term result is above 200 Bq/m³, you do not need to retest before acting. The next step is a plan to reduce the level, and our guide to radon mitigation explains what that involves.

Where should the detector go?

Put it in a normal occupancy area on the lowest lived-in level, which is a space people use more than four hours a day. A basement bedroom or rec room is the usual choice. Health Canada's guide gives these placement rules:

• Choose a space people occupy more than 4 hours a day, with bedrooms on the main floor or in the basement given priority.
• Avoid kitchens, laundry rooms and bathrooms.
• Place the device in the breathing zone, at least 30 cm (1 ft) above the floor.
• Keep it at least 30 cm from walls and ceilings, and at least 1 m from vents, windows, doors or anything that disturbs normal airflow.
• Keep it out of direct sunlight and away from heat sources, sump holes, crawl spaces and foundation cracks.
• Leave it where it will not be moved, and avoid high humidity.

The same guide asks residents not to change their lifestyle during a long-term test. Keep using the house as you normally do.

Which detector types are used?

The Health Canada guide lists passive devices, such as alpha track detectors and electret ion chambers, and active devices, which are electronic radon monitors. It recommends devices that have passed C-NRPP performance testing. Health Canada's page on testing your home adds that you can buy a do-it-yourself kit or hire a radon measurement professional.

A do-it-yourself kit can work if you follow the instructions exactly. A professional adds value when the home has several levels, when you need a report for a sale or an insurer, or when the first result is borderline and you want the placement checked.

When should I test again?

Health Canada's retest rules are specific. Use this checklist:

• Fewer than 91 days of your test fell in the heating season and the result was under 200 Bq/m³: test again in the next heating season.
• After renovations that affect the structure or ventilation, energy retrofits, significant excavation nearby, or new structural damage: test again in the next heating season.
• A previously untested floor becomes the lowest lived-in level, for example a finished basement: test it.
• After a mitigation system is installed: test again to confirm it works.
• Homes with an active soil depressurization or other active mitigation system: test every 5 years.
• A newly built home: test in the first heating season after occupancy, and again 2 years after the year of construction.

Two of those triggers matter after a loss. If a flood or a structural repair changed the lower level, the old result may no longer describe the house. Our article on indoor air quality after water damage covers the other air concerns that follow a wet basement.

How do I read the result?

Your report will give a number in becquerels per cubic metre. Compare a long-term average with 200 Bq/m³, and remember Health Canada's note that any measurement can be off by up to 25 percent. A result close to the guideline deserves a careful look at placement and test length, not a quick guess in either direction.

If the result is under the guideline but fewer than 91 days fell in the heating season, Health Canada says to test again in the next heating season. If it is over the guideline, move on to a plan to lower it, then test again once that work is complete.

What should I have ready before I call?

• Which level of the home people actually use most, and whether the basement is finished or has bedrooms.
• Any past radon result, with the date and test length.
• Renovations, leaks or foundation repairs since that result.
• Whether you are buying, selling, renting out the home or filing an insurance claim, since that changes what documentation you need.
• How soon you need an answer, so the right test type is chosen.

If the basement has recently flooded, the moisture and air quality questions run alongside the radon question. See our indoor air quality testing service for the other pollutants worth measuring, and our water damage restoration team if the lower level is still wet. Before any invasive work on an older house, read why asbestos testing comes first in older GTA homes.

Common mistakes that make a radon result useless

The most common mistake is acting on a short-term number alone. A low short-term reading can give false comfort, and a high one can start an expensive project before the long-term average is known. The second is putting the detector in the wrong spot, such as a bathroom or next to a sump. The third is testing only the upstairs. The test belongs on the lowest lived-in level.

A fourth mistake is stopping after one result. Houses change. Renovations, new finishing and repairs can all change how radon enters and moves, which is why Health Canada sets out retest triggers.

How does this connect to insurance and restoration?

Whether a radon test or a mitigation system is covered depends on your policy, so read it or ask your insurer before you book. FirstLine does not decide coverage. If a restoration loss on your property is being claimed, we bill your insurer directly for the approved work, and you pay only your deductible.

When you are ready, book radon testing and we will explain the right test for your home.