How do I test my home for radon properly, and when do I test again?

Test for 91 days or longer, with the heating season inside the window. Health Canada recommends 3 to 12 months, with at least 91 days of that in the heating season. Put the detector on the lowest level of the home that people live on, in a room someone uses every day. Then live as you normally do, because a long-term test measures the home as it is lived in, and do not open windows for the test. Your result is compared with Health Canada’s 200 Bq/m³ guideline; see what it means and how soon to act.

Test for at least 91 days, with the heating season included

Radon levels move hour to hour and season to season, so a short reading shows one moment, not the year. Health Canada’s guideline applies to the yearly average, and 91 days is the shortest test it recommends. Three to 12 months gives a better estimate of that average, and the longer the test runs, the closer it gets.

The heating season matters because of how a house behaves in the cold. Closed windows and doors and the stack effect pull more soil gas inside. A test in the colder months usually gives a conservative estimate of the yearly level, so Health Canada asks for at least 91 days of the test in that season.

Seasonal variation, early results

Lower in summer

Early finding of Health Canada's seasonal study, which compares three-month tests in each season with a full year. As of May 2026, 397 participants had finished a year; summer tests were below the twelve-month result on average in every region, and Central Canada's summer results averaged 13% below. Health Canada says these early numbers are not to be used to adjust a result or decide when to test.

Date

2026-05-22

Sample

397 participants with a full year of tests, as of May 2026

Source

Health Canada, Seasonal variation of radon in Canadian homes: early survey results (updated 22 May 2026)

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Health Canada’s seasonal study is still running. It says the early numbers are not to be used to adjust a result or to decide when to test, so the heating-season rule stands. During the test, live as you normally do, and do not open windows for it. Read the questions people ask about running a test.

You can start any time of year, but a low result outside the heating season needs a retest

You can start a long-term test in any month. A test of 91 days or more above 200 Bq/m³ counts whenever it started, and Health Canada recommends corrective action within a year, sooner as the level rises.

Retest rule for an off-season test

Retest if below 200

Health Canada's rule for a test with fewer than 91 days in the heating season: a result below 200 Bq/m³ may underestimate the annual average, so test again in the next heating season. A test of 91 days or more above 200 needs no retest before acting.

Date

2026-05-22

Sample

Not applicable

Source

Health Canada, Guide for radon measurements in homes (updated 22 May 2026)

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A low result from a test short on heating-season days needs a second test in the next heating season. Read the questions about a result out of season or near 200.

Put the detector on the lowest lived-in level, in a room people use every day

The detector goes in a normal occupancy area, which is a room where someone spends more than four hours a day. It goes on the lowest level of the home that people live on. If the basement is unfinished and rarely used, the main floor is the lowest lived-in level.

• Pick first: a bedroom
• Pick next: a basement playroom, if children use it
• Also count: family rooms, living rooms, dens and offices
• Skip: kitchens, laundry rooms, bathrooms and storage rooms
• A basement counts only if people use it as living space

Test a home above ground level too, including an upper-floor apartment. Pick the level, the room and the exact spot for your home.

Keep it away from kitchens, bathrooms, windows, vents, heat and electronics

Where the detector sits inside the room changes the result. Health Canada’s measurement guide sets these placement rules.

• At least 30 cm above the floor
• At least 30 cm from walls and the ceiling
• At least 1 m from windows, doors and vents
• With room for air to move around it
• Where it will not be moved, and out of reach of children and pets
• Away from direct sunlight, heat sources, electronics and network equipment
• Not in a closet, drawer or crawl space, beside a sump or next to an open foundation crack

Four conditions weaken a result. They are a test shorter than 91 days, a damaged or tampered device, fewer than 91 days in the heating season, and placement that strayed from the guidance.

Survey quality controls

99.5% and 97%

Quality results of the 2024 Cross-Canada Radon Survey: detectors exposed to known amounts of radon matched them 99.5% of the time, and true duplicates placed side by side agreed 97% of the time. These figures describe the survey's own testing, not every device on the market.

Date

2024-10-01

Sample

Not applicable

Source

Cross-Canada Radon Survey 2024 report, Version 1.1 (CCSR.24.1.1), October 2024

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Repeated results may vary by up to plus or minus 25% under the CSA and ANSI standards Health Canada cites, so a result near 200 can sit on either side. Check whether your test met the conditions and what the number means.

A short test cannot tell you whether to mitigate

Health Canada says a short-term reading is not appropriate for a mitigation decision, because the guideline applies to the yearly average. A spike above 200 Bq/m³ does not mean the yearly average is over 200, and a few weeks below does not prove it is under. Use the longest average you have, never less than 91 days.

One detector is enough, and there are four ways to get one.

• Buy a long-term kit: place it, wait, then mail it to the lab
• Buy an electronic radon monitor: readings on a screen, an app or a web dashboard
• Borrow a monitor from a library: a first look, not a final answer, because loans are short
• Hire a certified measurement professional: the placement, the test and the report done for you

Long-term test kit cost

$30 to $60

Published cost of a long-term alpha track detector with lab analysis, as stated in CMAJ in 2023. Community and public programs sometimes offer kits for less or free. A published figure, not a current price.

Date

2023-06-19

Sample

Not applicable

Source

CMAJ 2023, Radon and lung cancer risk

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A professional makes sense when you need a report that meets Health Canada’s criteria: a landlord documenting a rental, a post-mitigation check, or a grant that asks for documents. A proper report holds the test dates, the result in Bq/m³ with its uncertainty, a comparison to the guideline, and any condition that weakens the test. No government or academic source publishes a price for professional testing. Get quotes from two C-NRPP certified professionals; find one in the directory. Health Canada says to test before you sell and after you buy, not during the sale; see how testing works in a home sale.

Health Canada recommends long-term devices that passed C-NRPP performance testing and favours none over another. Some consumer monitors store less than three months of data. Health Canada says to consider replacing one five years after purchase unless it has been recalibrated, and many consumer monitors cannot be. See which devices are listed and how monitors perform.

Retest after renovations or energy retrofits, after a mitigation system goes in, and on a regular schedule

A result describes the home as it was during the test. After any of these changes, Health Canada recommends a new test in the next heating season.

• A renovation that changes the structure or ventilation, such as finishing a basement, a new furnace or an added bathroom
• An energy retrofit such as new windows, insulation or sealing
• Major excavation or earthwork next to the home
• New structural damage to the slab or basement walls
• The basement or main floor becoming the lowest lived-in level
• The installation of a mitigation system

New-build testing schedule

2

tests

Health Canada's schedule for a newly built home: test in the first heating season after occupancy, then retest two years after the year of construction.

Date

2026-05-22

Sample

Not applicable

Source

Health Canada, Guide for radon measurements in homes (updated 22 May 2026)

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A home with an active soil depressurization system gets a long-term test after the system is installed, then a retest every five years. That rule is separate from the five-year replacement advice for a consumer monitor. See the tests that follow a mitigation system.

Households that had tested

9

%

Share of households outside apartment buildings that had heard of radon and had ever tested for it, in 2021; 56% of households had heard of radon. A 2021 figure, not a current rate.

Date

2022-10-18

Sample

Households and the Environment Survey, 2021

Source

Statistics Canada, The Daily, 18 October 2022: Households and the Environment Survey, radon awareness and testing, 2021

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Health Canada’s own figure, in its radon action guide for provinces and territories, is that more than 90% of Canadian homeowners have never tested. Find out whether your home needs a new test now.