How long should a radon test run?
Health Canada recommends a long-term measurement of at least 91 days.
Radon changes from hour to hour, day to day and season to season. A longer measurement gives a more representative estimate of the annual average than a short snapshot.
For a result below 200 Bq/m³, Health Canada’s 2026 guide says that if fewer than 91 days of the test occurred during the heating season, the home should be re-tested during the next heating season.
Where should the detector go?
Place it on the lowest level where someone normally spends about four or more hours a day.
- Keep it at least 30 cm above the floor and at least 30 cm from walls or ceilings.
- Keep it at least 1 m from windows, doors, vents and other sources of moving air.
- Leave space around it and keep it away from electronics, high humidity and direct sunlight.
- Do not move it during the measurement period; follow the manufacturer’s instructions.
DIY kit or professional measurement?
Both can be legitimate when the device and process meet current guidance.
A homeowner can use a long-term kit and follow its directions. If choosing an electronic monitor, Health Canada recommends selecting one that has passed C-NRPP performance testing for long-term measurements.
A C-NRPP-certified measurement professional can be useful when placement is complex, documentation matters or you want help interpreting the testing plan.
Common testing mistakes
- Making a mitigation decision from an hourly or daily spike.
- Testing for fewer than 91 days and treating the number as an annual average.
- Placing a detector in a sump, crawlspace, furnace room, bathroom or other location that is not normally occupied.
- Moving the detector or placing it close to windows, doors, vents or electronics.
- Ignoring the test provider’s handling and return instructions.
What happens after testing?
Compare a valid long-term average with Canada’s 200 Bq/m³ guideline. A result above the guideline is information you can act on—not a reason to panic. A qualified professional can assess the home and recommend an appropriate mitigation design.