Canadian houses stay shut for months. The furnace pulls air, and the house pulls soil gas with it. That is when exposure is often highest, and when Health Canada wants the measurement.

October to April

A 91-day detector set out in November finishes in February, in the middle of the heating season. One set out in May mostly describes summer, with windows open. The number is still a number. It is a weaker stand-in for the year.

If you cannot wait for winter

A 4-day test is for a purchase deadline or a first look at one room. Say so when you share the report. 4 days or 91 days.

The 4-day test is a first reading. The 91-day test is the length Health Canada uses to judge a full heating season. Both are $59 before tax. Shipping, the prepaid return, and the lab are included. Tax is extra. The PDF report is emailed within 2 business days after the lab receives the detector.

Above 200 Bq/m³, the fix is a fan that pulls soil gas from under the slab and exhausts it above the roof. Radon Gas is C-NRPP certified for testing and for mitigation, and ships kits across Canada. Start from the Canada test page.