To test your home for radon, buy a long-term test kit approved for use in Canada, hang it in a normally occupied room on the lowest lived-in level of your house, and leave it there for at least 91 days during the heating season before mailing it to the lab. If the result comes back above 200 becquerels per cubic metre, Health Canada recommends fixing the problem within a year, and that repair is a job for a certified professional rather than a weekend project.
The timing matters, which is why this is a September task rather than a January one. Health Canada’s Guide for radon measurements in homes is explicit that a valid test must run a minimum of 91 days, and that a minimum of 91 of those days must fall during the heating season, the stretch of colder months when your furnace or heat pump is actually running. Indoor radon levels climb in winter because windows stay shut and the stack effect of warm air rising through the house pulls more soil gas in through the foundation. A test run in July will almost certainly understate what your family breathes in February. Start a kit in late September or October and you clear the 91-day heating-season requirement comfortably before spring.
Radon is a colourless, odourless radioactive gas produced by uranium decaying in soil and bedrock. It seeps into houses through cracks in foundation slabs, sump pits, floor drains, and gaps around service pipes, then accumulates in enclosed indoor air. Health Canada estimates roughly one in five Canadian homes has a high radon level, that radon exposure accounts for about 16 per cent of lung cancers in this country, and that it causes more than 3,000 lung cancer deaths a year. It is the leading cause of lung cancer among people who have never smoked. Levels vary house by house, so a neighbour’s reading, a regional map, or the age of your home tells you nothing reliable about your own. Testing is the only way to know, and it is genuinely simple, cheap, and safe to do yourself. November is Radon Action Month in Canada, and lung associations and municipalities in several provinces run free or subsidized kit programs each fall, so it is worth checking locally before you buy.
How to test your home for radon, step by step
- Buy a long-term kit that is approved for Canadian use. Look for an alpha-track or electret kit rated for 91 days or longer, purchased from a supplier whose lab is certified through the Canadian National Radon Proficiency Program (C-NRPP). Take Action on Radon maintains a vetted list of kit providers by province, including provincial lung associations. Confirm whether lab analysis and return postage are included in the price, because that varies between suppliers. If you would rather use a digital electronic radon monitor, check it against the C-NRPP consumer-grade monitor report first. Health Canada has recalled several inexpensive radon detectors sold online for inaccurate readings.
- Choose the lowest lived-in level of the house. Health Canada defines this as the floor containing a normal occupancy area, meaning any space where someone spends more than four hours a day. A finished basement rec room or home office counts. An unfinished crawl space or a cold cellar you visit twice a month does not, and testing there will give you a number that overstates your actual exposure. If your lowest lived-in level is the main floor because nobody uses the basement, test the main floor. Homes with no floor in contact with the ground, including upper-storey condominium units, should still be tested.
- Position the detector properly. Place it in that room where it will not be disturbed for three months, with open air circulating around it. Keep it off the floor and away from exterior walls, either suspended from the ceiling or sitting on a shelf or side table. Wipe the surface it will rest on with a dry cloth first.
- Avoid the placements that spoil results. Health Canada’s guide lists these specifically: do not put the detector in contact with the floor, ceiling, or an exterior wall; do not put it in a closet, drawer, or other enclosed space; do not put it in a humid spot such as a bathroom, sunroom, or beside a humidifier; do not put it near a heat source or in direct sunlight, including windowsills and spots above a radiator or fireplace; do not put it in the air current from a heating or ventilation register or near a window; and do not set it on or beside computers, routers, televisions, or speakers, which can interfere with some devices.
- Write down the start date and leave it alone. The 91-day minimum is a hard floor, not a target. Note the exact date you opened and placed the kit, and set a calendar reminder for the retrieval date. Many homeowners simply run the kit from October through February, which builds in a margin.
- Live normally for the duration. Do not open extra windows, run additional fans, or otherwise change your heating and ventilation habits to improve the number. The point of a long-term test is to measure the air your household actually breathes under ordinary conditions.
- Retrieve and mail the kit promptly. When the test period ends, record the closing date, seal the detector according to the manufacturer’s instructions, and send it to the lab right away. Delays after the seal can affect the result on some device types.
- Read the result against 200 Bq/m³. The Canadian radon guideline is 200 becquerels per cubic metre as an average annual level. Below that, Health Canada does not recommend corrective action, though you may still choose to reduce your level further. If your test ran fewer than 91 days during the heating season and came back below the guideline, re-test properly, because a short or off-season test can underestimate the annual average.
- If you are above the guideline, hire a certified mitigation professional. Health Canada recommends mitigating within one year for any level above 200 Bq/m³, and sooner the higher the reading. Do not attempt this yourself. The standard fix is an active soil depressurization system, which involves cutting through the foundation slab, sealing entry points, and installing a sealed vent stack and fan sized to the house. Done wrong it can fail entirely or, worse, depressurize the house enough to cause a fuel-burning appliance to spill combustion gases indoors. Use the C-NRPP directory to find a certified mitigation professional in your area, and get more than one quote.
- Re-test afterward, and again down the road. Testing is the only way to confirm a mitigation system is working. Health Canada recommends re-testing homes with active mitigation systems every five years to confirm the system is still doing its job. Re-test as well if a basement or main floor that was never tested becomes your lowest lived-in level, for example after finishing a basement.
The whole exercise costs less than a tank of gas and about fifteen minutes of your attention spread across three months. The hardest part is remembering to start it, which is exactly why the beginning of heating season is the moment to order a kit. If the number comes back low, you have a definitive answer for your own house rather than a guess based on your postal code. If it comes back high, you have found a fixable problem years before it could have done real damage.
Sources: Health Canada, Guide for radon measurements in homes (updated May 2026), for test duration, heating-season timing, detector placement, the 200 Bq/m³ guideline, the one-year mitigation recommendation, and the five-year re-test interval; Health Canada, Radon: Reduction Guide for Canadians, for mitigation methods; Health Canada, Radon causes lung cancer, for the health-risk figures; and Take Action on Radon, for C-NRPP-approved kit suppliers and the list of recalled consumer radon detectors.
