How to Test for Radon in Your Home

Radon is produced continuously by the natural decay of uranium in soil and rock, and it is present at some concentration in nearly every Canadian home. Outdoors it disperses quickly and is not a concern. Indoors, particularly in basements and lower levels with limited air exchange, it can accumulate to concentrations that carry a measurable long-term health risk. Health Canada material on radon awareness states that roughly one in five Canadian homes has radon levels above the guideline, and attributes more than 3,000 lung cancer deaths a year in Canada to radon exposure, making it the second leading cause of lung cancer after smoking.

The risk is not distributed evenly between smokers and non-smokers. Health Canada's guidance for health professionals estimates that a non-smoker exposed to 200 Bq/m³ over a lifetime faces roughly a 2% chance of developing lung cancer from that exposure, while a smoker exposed to the same concentration faces a risk closer to 17%, reflecting a multiplicative rather than additive interaction between radon and tobacco smoke. This is one reason Health Canada frames testing as relevant to every household and every dwelling type, rather than only homes in regions with a reputation for elevated readings.

Why a three-month measurement is the standard

Indoor radon concentration is not constant. It shifts with temperature, wind, barometric pressure, and how a home is heated and ventilated, and it is typically highest during colder months, when a home is sealed tightly and indoor heating creates a stack effect that draws soil gas upward through foundation cracks and utility penetrations. Health Canada's Guide for Radon Measurements in Residential Dwellings sets the minimum test duration at 91 days, run in the normal occupancy area of the home, defined as the zone where residents spend at least four hours a day on average over the course of a year, so the result reflects a genuine annual average rather than a single weather event.

Short-term tests of two to seven days, usually run with charcoal canisters, have a role in time-sensitive situations such as real estate closings, but Health Canada and provincial radon programs treat them as a screening step rather than a substitute for a long-term result. A low short-term reading taken in summer can understate winter exposure, and a high one taken during unusually cold or windy weather can overstate it. Any detector used for a decision you plan to act on should be listed by the Canadian National Radon Proficiency Program (C-NRPP), which sets quality standards for both devices and the professionals who deploy them.

How your result compares to national data

Health Canada's reference point for regional radon potential is the 2012 Cross-Canada Survey of Radon Concentrations in Homes, which placed long-term detectors in more than 14,000 homes nationally. It remains the most widely cited estimate of regional radon potential, though it drew from a voluntary sample rather than a random one. More recent citizen-science work coordinated by Take Action on Radon, a Health Canada funded initiative, has found elevated-result rates well above the national 7% estimate in a number of participating communities through its 100 Radon Test Kit Challenge program. The takeaway for homeowners holds either way: regional figures are useful context, but they cannot predict the reading in a specific house, which depends on foundation type, sump design, and how tightly the building envelope is sealed as much as on the soil underneath it.

Provincial and municipal testing programs

• Take Action on Radon distributes free long-term test kits through its 100 Radon Test Kit Challenge, which partners with municipalities that have limited existing test coverage.
• C-NRPP maintains a public directory of certified measurement professionals for anyone who prefers a professional deployment over a self-administered mail-in kit, useful in real estate transactions with a tight timeline.
• Provincial and territorial health authorities in several provinces distribute or subsidize kits seasonally; check with a local public health unit before buying a kit at full retail price.

Radon and real estate transactions

Radon has become a more common line item in Canadian home inspections and offers, but a short-term test taken during a closing window is a screening tool. Buyers who receive only a short-term result should plan to run a long-term test after taking possession, ideally starting in the fall, and treat any pre-closing number as provisional. Sellers with a recent long-term result on file are generally in a stronger negotiating position than sellers with no radon history, since the alternative leaves a buyer to assume the worst case.

After you get a result

A result below 200 Bq/m³ does not mean radon exposure is zero, since Health Canada does not consider any concentration fully risk-free. Homeowners below the guideline can reasonably retest every two years, or after any renovation that changes the foundation, ventilation, or heating system. A result at or above 200 Bq/m³ should move directly to planning mitigation, and results above 600 Bq/m³ warrant action within a year rather than a longer planning window. The radon mitigation guide covers what a sub-slab depressurization system involves, what it costs, and how to verify it worked. For a broader look at how radon geology and the national guideline fit together, see the OpenStats indoor radon guide.