Short answer
Yes, you can have a useful answer in as little as 2 weeks. A calibrated professional monitor logs radon every hour, and a heating-season reading far above or below Health Canada’s 200 Bq/m³ guideline usually holds up over three months. A reading near 200 doesn’t. Health Canada bases decisions on a test of at least 91 days, so the long-term test always runs to the end.
Key facts
- Early reading: day 14, from a calibrated continuous monitor that logs every hour.
- Full result: day 91 or later, from a long-term detector placed the same day.
- 400 Bq/m³ or more early: very likely high. You can book the fix now.
- Near 200: wait for day 91. Under 100 in winter: probably fine, but finish the test.
Two devices, one visit
On placement day we set up two devices side by side on your lowest lived-in level. A long-term detector stays for at least 91 days: that’s the test Health Canada’s guideline is built on. Next to it, a calibrated professional continuous monitor records radon every hour for the first two weeks. Then we collect the monitor and send you your early reading. The long-term detector stays put.
C-NRPP, Canada’s radon certification program, counts any measurement from 48 hours up to three months as a short-term test, and says every short-term result should be followed by a long-term one. That’s how this works: the early reading is a short-term test, and the long-term test is never skipped.
How accurate is a 2-week reading?
It depends on how far the reading is from the line. Radon rises and falls with the weather, and a short test averages over fewer of those swings. When a home is far from 200, the swings rarely push its average across. When it’s close, they easily can.
- A study in Iowa compared 7 to 10 day winter basement tests with each home’s annual basement average. The short test correctly flagged homes above the U.S. action level of 148 Bq/m³ about 88% of the time.
- A 2024 review of 20 studies found that one-week tests predicted the annual average with over 95% confidence when levels were low, but were right only about half the time at moderate levels.
Two weeks is longer than the tests in either source, and an hourly log shows whether a reading was steady or driven by a storm or a few cold nights. The pattern still holds: an early reading is strong evidence at the extremes and weak evidence near 200.
What your early reading means
| Early reading (2 weeks) | What it likely means | What we suggest |
|---|---|---|
| 400 Bq/m³ or more | Very likely above 200 over 91 days | Book a mitigation assessment now if you’d rather not wait. |
| 100–399 Bq/m³ | Could land on either side of 200 | Wait for the 91-day result. |
| Under 100 Bq/m³ (heating season) | Very likely below 200 | Probably fine. Finish the test to be sure. |
The 400 cut-off is double the guideline. It’s our own judgement, set cautiously, not a published rule. Health Canada and C-NRPP both say to base a mitigation decision on a long-term test, and we follow that: the early reading tells you how urgent the question is, and the 91-day test answers it.
If you act on a high early reading
Health Canada allows up to two years to reduce levels between 200 and 600 Bq/m³, so there’s rarely a medical reason to rush. People act early because they’d rather not spend a winter waiting, or because someone sleeps in the basement. If you do:
- The long-term detector comes out on install day, because a running system changes what it measures.
- A new long-term test starts after the install. That becomes the number that matters: proof the system worked, and the result our guarantee is based on.
- An early reading of several hundred Bq/m³ or more is also a good reason to spend less time on the lowest level until the fix is in.
Why the early reading works best in winter
Radon usually peaks in the heating season, when the stack effect is strongest and windows stay closed. Both sources above are about winter testing, and the 2024 review found winter readings more representative of the year. A low two-week reading in July says less, because summer levels are often below the annual average. We run early readings all year, but a low one in summer is a reason to finish the test, not to relax.
Can my own digital monitor give me an early reading?
A consumer monitor is great for watching trends, and if it shows a high average over a couple of weeks, that’s a good reason to book a long-term test. It isn’t a substitute for a calibrated professional instrument, though, and a buyer, a lender or a Tarion claim will want results from a C-NRPP certified professional. Our early reading comes from a professional monitor, placed to Health Canada’s protocol.
Common questions
Can I get radon test results in 2 weeks?
Yes, as an early reading from a calibrated professional monitor that logs radon every hour. The full long-term result follows at 91 days or later, which is what Health Canada bases its guideline on.
Is a 2-week radon test accurate?
When the reading is far from Health Canada’s 200 Bq/m³ guideline, it’s usually a reliable signal, especially in winter. Near 200, short tests are close to a coin flip, so that’s when you wait for the 91-day result.
If my early reading is high, do I still need the 91-day test?
We recommend finishing it. If your early reading is 400 Bq/m³ or more and you’d rather not wait, you can book the fix now. A long-term test after the install then confirms the system worked.
If my early reading is low, can I stop the test?
We recommend letting it run. A low winter reading is encouraging, but radon changes from week to week, and the 91-day result is the one Health Canada’s guideline, real estate buyers and Tarion rely on.
Sources
- Health Canada — Guide for Radon Measurements in Residential Dwellings (Homes)
- C-NRPP — Protocol for Conducting Short-Term Radon Measurements (2018)
- Barros, Steck & Field, Health Physics (2014) — winter short-term vs. annual radon in Iowa basements
- Mphaga et al., Sensors (2024) — Short-term vs. long-term: a critical review of indoor radon measurement
- Health Canada — Government of Canada radon guideline