Radon testing and long-term monitoring in Guelph

Health Canada's 2012 survey found 10.9% of 92 homes tested in the Wellington-Dufferin-Guelph Health Unit health region above the guideline. The larger 2024 Cross-Canada survey reports 13.5% (1 in 7) of houses at or above the guideline for the Guelph, ON (Guelph CMA) metro area.

The two surveys aren't directly comparable: the 2024 study pooled about 69,000 volunteer tests and more of them were taken in basements, which partly explains its higher numbers. Neither can tell you about a single house, because neighbouring homes can differ widely.

Health Canada's measurement guide asks for a long-term test with at least 91 days in the heating season, when closed windows and the stack effect make readings higher, so the result is a conservative estimate of the yearly average. It recommends testing for 3 to 12 months. Our radon testing guide walks through each step.

Place the detector on the lowest level where someone spends more than four hours a day, at least 30 cm above the floor and 30 cm from walls, and at least 1 m from vents, windows and doors; avoid kitchens, laundry rooms and bathrooms. The choice of device:

• Alpha track detectors record radon's alpha particles on a plastic film; you mail them to a lab when the test ends. A long-term kit costs about $30–$80 including the lab fee (Windsor-Essex County Health Unit).
• Electret ion chambers lose charge as radon ionizes the air inside; a lab reads the voltage drop.
• Digital (electronic) monitors read continuously and show results on a screen or an app, and cost more (Lung Saskatchewan sells one for $189). For a long-term test, Health Canada says to use one that has passed C-NRPP performance testing, and it still has to run at least three months.
• Continuous monitoring after mitigation: a digital monitor left running lets you watch for changes between the follow-up long-term tests Health Canada recommends.

• There's no provincial free-kit program, but many Ontario public libraries lend digital radon monitors free with a library card, among them Hamilton, Vaughan, Guelph, Kingston Frontenac, Greater Sudbury, Thunder Bay, Brantford and Waterloo.
• For a professional measurement or mitigation, search the C-NRPP directory by your Guelph postal code; it lists certified measurement and mitigation professionals.

Health Canada recommends fixing levels above 200 Bq/m³ within a year, and sooner the higher the level. The usual fix is a sub-slab depressurization system (a sealed pipe through the floor and a fan venting outside), which Health Canada says costs about $2,000 to $3,000 including material and labour and cuts radon by more than 80% in most homes. Hire a professional certified for mitigation under C-NRPP. After a system goes in:

• A C-NRPP professional runs a short test starting at least 24 hours after the fan is turned on.
• A long-term three-month test follows in the next fall or winter, done by a company other than the installer.
• With an active system, Health Canada recommends a long-term test within two years of activation and every five years after that, and again after renovations.
• Check the system's pressure gauge (manometer) regularly and never switch the fan off. It costs about $50 to $75 a year to run; a replacement fan is $200 to $300.

• Since January 1, 2025, the Ontario Building Code requires new houses to include a soil-gas barrier and a radon rough-in.
• Tarion's new-home warranty covers radon remediation for seven years from possession, and the Canadian Lung Association's Lungs Matter program offers up to $1,500 toward mitigation for households with low to moderate incomes or a lung cancer diagnosis.