Here is how to choose based on your situation, and the pitfalls that skew a measurement.
Two families of devices, two uses
Short-term kits (a few days) give a first signal: they cost little and allow screening. Their limit lies in radon’s heavy fluctuation: a passing spike can frighten without reason, a lull can falsely reassure. They help decide whether a long-term test is worth doing, not whether action is needed.
Long-term continuous detectors tell the full story: they record concentration week after week, ideally through heating season. This is the kind of measurement — at least three months — that allows a true comparison against the 200 Bq/m³ guideline.
In between, some electronic “smart” monitors tempt with real-time readings. They are useful for observing variation and checking the effect of opening a window, but their consumer-grade calibration looks weak next to an approved device used per protocol.
What a certified professional adds
Measuring sounds simple until you list the requirements: right floor, right location, right ventilation conditions, sufficient duration, proper report interpretation. A professional holding a recognized certification (for example C-NRPP or equivalent), applies that protocol to the letter and documents the outcome.
Their report also carries more weight in certain contexts. For a property transaction, a dispute or an insurance file, a signed document from a certified person beats a screenshot from a home device, however good the device.
Finally, the professional reads the house while measuring: potential gas entry points, foundation layout, feasibility of a future mitigation system. That holistic view guides next steps when the annual average exceeds the 200 Bq/m³ guideline.
Common pitfalls that skew a measurement
Pitfall number one remains placement. A detector sitting in a bathroom (humidity), against a window (draft) or inside a closed closet (stagnant air) produces a number representing neither the household’s exposure nor the home’s.
Second pitfall: timing. Testing during a summer heat wave with windows wide open amounts to testing the outdoors. The useful window sits in heating season, with the home lived in normally and no deliberate over-ventilation.
Third pitfall: drawing conclusions from a single short-term result. Before investing in work (or panicking for nothing), confirm with a well-placed long-term test. That standard aligns your decision with the official reference rather than with chance.
And after the result?
Result clearly below the 200 Bq/m³ guideline: record it with the date and testing duration, then schedule a recheck in a few years or after major foundation work. A level below the guideline is not risk free — Health Canada says so — and the level you accept is your own decision.
Borderline result: repeat a strict long-term test, or bring in a certified professional to break the tie. This is the zone where decision errors are most costly, in both directions.
Result above the reference: move to mitigation planning with someone certified for mitigation itself. The same credential does not always cover both testing and correcting: explicitly ask which certification backs each stage of the work.
Verified and sourced
Verified on September 27, 2026
Official sources
What these numbers do not cover
The choice of measurement method follows Health Canada’s published method, which recommends a long-term test of at least three months; the 200 Bq/m³ guideline applies to the annual average, and this guide sets no measurement price.