A note before you read. This is general consumer information for Canadian homeowners, buyers, sellers, and renters, drawn from publicly available Health Canada, University of Calgary / Evict Radon, and peer-reviewed sources. It is not medical, legal, or warranty advice. Radon results are reported against the Health Canada guideline of 200 Bq/m³; RadonTest.ca coordinates testing logistics and does not interpret individual results or provide health assessments. This article is about how long a test should run (the duration decision) — for which kind of device to use, see our long-term test vs digital monitor guide, and for when to start, see when is radon testing season in Canada.
Key facts at a glance
- Health Canada recommends a long-term test of at least 91 days (about three months) to decide whether to take action on radon. It does not recommend any test shorter than one month for that decision.
- Short-term tests (roughly 2–7 days) are for screening or for checking a mitigation system right after it's switched on — not for deciding whether to fix your home.
- A University of Calgary study found short-term kits were "imprecise up to 99% of the time" compared with a long-term test in the same homes (Goodarzi et al., Scientific Reports, 2019).
- Radon swings 2–3× over a single day and even more from season to season, so a few days can't represent your real annual exposure.
- The heating season (roughly October–April) is ideal, but you can start a long-term test any time of year.
- A long-term result above 200 Bq/m³ means Health Canada recommends acting within one year — sooner the higher the level.
The short answer
Health Canada recommends a long-term radon test that runs for at least 91 days — about three months — to decide whether to reduce the radon in your home. That is the duration that produces a result you can act on.
Health Canada does not recommend a test under one month for making that decision. A two-day, three-day, or seven-day "short-term" test has a legitimate but narrow role — screening and system checks (more on that below) — but it is not the basis on which you should decide to spend money mitigating, file a warranty claim, or close a real-estate deal.
So if the question is "how long should my radon test run?", the answer for almost every homeowner is simple: at least 91 days, ideally during the heating season. The rest of this article explains why the duration matters so much, and the handful of situations where a short test is the right tool.
Why long-term is more accurate
Radon is not a steady number. It rises and falls constantly, driven by weather, air pressure, how your furnace and fans move air, and whether your windows are open or shut. Health Canada and Canadian researchers describe radon levels that vary by a factor of two to three over a single day, and by even more from one season to the next — winter readings are typically far higher than summer ones, because a sealed, heated home draws more soil gas indoors.
That variability is exactly why a snapshot misleads you. A test that runs for a few days captures whatever the weather happened to be doing that week. It might land on an unusually breezy stretch and read low, or a cold, still spell and read high — and neither tells you your true average. A test that runs for 91 or more days averages across all of that noise, so the number reflects your real, year-round exposure — which is what the health risk actually depends on, since radon harm comes from long-term exposure, not a single day.
There's a second, practical problem with the cheap short-term option. Most short-term kits sold to consumers are charcoal (activated-carbon) detectors, and charcoal is sensitive to drafts and humidity, and it keeps absorbing and releasing radon after you seal it up — so any delay in the mail on the way back to the lab can skew the result. A long-term alpha-track detector doesn't have that problem: it records a cumulative track of radon over the whole exposure period, so a day or two in transit doesn't change the answer. (For more on why kit type matters, see are radon test kits accurate in Canada and our look at hardware-store radon test kits.)
The 99% finding
The clearest Canadian evidence on this comes from the University of Calgary, through the scientist-led Evict Radon initiative. In a study published in Scientific Reports in 2019 (Goodarzi et al.), researchers placed two detectors — a short-term (five-day) kit and a long-term (90-day) kit — in the same homes, across both summer and winter. The finding:
The short-term kits were "imprecise up to 99% of the time" when compared with the long-term test.
That is the figure, quoted exactly. It does not mean the short-term kits were "wrong 99% of the time" in some absolute sense — it means that, the great majority of the time, the short-term reading did not reliably predict the home's true long-term level. As the study's lead, Dr. Aaron Goodarzi, put it:
"Short-term tests can give a false sense of alarm, or worse, a false sense of security, as they cannot precisely predict long-term exposure."
That "false sense of security" is the real danger: a short test can come back comfortably low and convince a family they're fine, when a proper 91-day measurement over the heating season would have shown a level worth fixing.
Crucially, Health Canada endorsed the takeaway. Kelley Bush, Health Canada's manager of radon education and awareness, said the research "provides Canadian data that confirms the value of long-term testing" — the recommendation Health Canada had already been making. In other words, this isn't one lab's opinion; it's Canadian data that the federal health authority points to in support of long-term testing.
When is a short-term test actually appropriate?
Short-term tests are not useless — they're just for different jobs than the "should I mitigate?" decision. The legitimate uses:
- Quick screening. If you want a fast, rough indication of whether radon is likely an issue at all, a short-term test can flag a high reading. But a low or borderline short-term result must always be confirmed with a long-term test before you conclude your home is fine.
- Pre-mitigation diagnostics. A C-NRPP-certified mitigation professional may use short-term measurements (or continuous monitors) to diagnose a home, find entry points, and plan a system. That's a professional diagnostic step, not a homeowner's decision tool.
- Checking a mitigation system right after it's activated. After a radon system is installed, a short-term test is the normal way to confirm the fan is doing its job quickly — before the homeowner has lived with it for a season. This is always followed by a long-term test the next heating season to confirm the system is holding the level down over time, ideally not by the company that installed it.
The common thread: in every legitimate case, a short-term test is a screen or a check, and the real decision still rests on a long-term measurement.
What about real estate / a 48-hour test?
This is where people get confused, because the rules differ by country, and the difference matters.
In the United States, the EPA permits short-term tests for real-estate transactions — a closing can move on a 48-hour test placed under "closed-house conditions," precisely because property timelines are too fast for a 90-day test. That's a US position, driven by deal speed.
In Canada, the guidance favours long-term testing even for transactions. Health Canada's measurement recommendation for deciding on a home is the 91-day long-term test, and Canadian researchers have actively steered the real-estate industry away from short-term kits: the University of Calgary worked with the Real Estate Council of Alberta (RECA) to educate realtors against using short-term radon kits in real-estate deals, "in the absence of reliable short-term testing." So the "short-term is allowed" position belongs to the EPA (US); the "favour long-term" position is the Canadian one.
What does that mean if you're buying or selling on a normal closing timeline? You generally can't run a 91-day test before completion — so the practical Canadian approaches are a documented radon holdback or post-closing testing clause, or making a long-term test a condition where timelines allow, rather than relying on a 48-hour number. We walk through the options in our guide to radon when buying or selling a home in Canada.
Long-term test vs digital monitor
A reasonable next question is "should I use a long-term lab kit or a continuous digital monitor?" — but that's a different question. That one is about device type, not test duration, and the trade-offs (a one-time lab-analysed measurement for the decision, versus an electronic monitor you keep) are covered separately in long-term radon test vs digital monitor.
Frequently asked questions
How long does a radon test take? For a result you can act on, at least 91 days — about three months — for a long-term test, plus lab turnaround. Health Canada recommends long-term testing because radon varies too much day to day for a shorter test to reflect your real exposure.
Is a short-term radon test accurate? Not for deciding whether to fix your home. A University of Calgary study found short-term kits were "imprecise up to 99% of the time" compared with a long-term test in the same homes. Short-term tests are for screening or for checking a mitigation system, not for the mitigation decision.
Is a 48-hour radon test enough? Not in Canada for making a decision. The US EPA allows short-term tests (including 48-hour ones) for real-estate timelines, but Health Canada's guidance favours a long-term test of at least 91 days, and a 48-hour reading can't capture radon's day-to-day and seasonal swings.
Can I use a short-term test for a home purchase? The EPA permits it in the US, but Canadian practice favours long-term testing — University of Calgary researchers worked with the Real Estate Council of Alberta to steer realtors away from short-term kits. On a fast closing, a documented holdback or post-closing long-term test is the usual Canadian approach. See our real-estate guide.
How long is a long-term test? At least 91 days (about three months), and it can run up to a year. Ninety-one days is the minimum valid measurement period for a long-term test under Health Canada's guidance.
When should I start? You can start any time of year. The heating season (roughly October–April) is ideal because closed-up winter homes give a conservative reading, but a high result is worth acting on in any season and a low off-season result is worth confirming over a winter. See when is radon testing season in Canada.
Where do I put the detector? In the lowest lived-in level of the home, in a room used more than four hours a day, about 30 cm off the floor and away from drafts, vents, and direct sun — not the kitchen, bathroom, or laundry room. See where to place a radon test kit.
Test your home the way Health Canada recommends
The duration decision is the easy part: run a long-term test for at least 91 days, ideally over the heating season, and act on the result.
Order your RadonTest.ca kit → — a long-term (91+ day) alpha-track kit, lab analysis by a C-NRPP-certified laboratory (with an all-in-Canada analysis option), tracked shipping both ways, and your result delivered with clear Health Canada context.
Sources
- Health Canada — Guide for radon measurements in residential dwellings (long-term test of at least 91 days; heating-season guidance; does not recommend short-term tests for decisions), modified 2025-12-22. https://radontest.ca/links/hc-measurements-guide
- University of Calgary — UCalgary research finds short-term radon test kits not effective in measuring radon gas exposure (short-term kits "imprecise up to 99% of the time"; Dr. Goodarzi "false sense of security"; Health Canada "confirms the value of long-term testing"; RECA collaboration), Dec. 5, 2019. https://ucalgary.ca/news/ucalgary-research-finds-short-term-radon-test-kits-not-effective-measuring-radon-gas-exposure
- Goodarzi A. et al. — Comparison of short-term and long-term radon measurements (study comparing 5-day and 90-day kits in the same homes), Scientific Reports, 2019. https://www.nature.com/articles/s41598-019-54891-8
- Take Action on Radon — Radon test kits (long-term testing guidance for Canadians). https://takeactiononradon.ca/test-for-radon/radon-test-kits/
Lab analysis is performed independently by a C-NRPP-certified laboratory. Results are reported against the Health Canada guideline of 200 Bq/m³. RadonTest.ca coordinates kit logistics and sample submission only — it does not interpret or modify lab results and does not provide medical, legal, or warranty advice. Information attributed to Health Canada, the University of Calgary / Evict Radon, and others is summarized from the public sources listed above; confirm time-sensitive details with the responsible body.