A note before you read. This is general consumer information for Canadian homeowners, buyers, sellers, and renters, drawn from publicly available Health Canada and Take Action on Radon 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. The placement specifics below follow Health Canada's measurement guide — for how long the test should run, see short-term vs long-term radon test in Canada, and for when to start, see when is radon testing season in Canada.
Key facts at a glance
- Test the lowest lived-in level of your home — the lowest floor where you (or anyone) spend at least four hours a day. A finished basement counts if it's actually used.
- Choose a room used at least 4 hours a day — a bedroom, living room, rec room, or home office. Not a bathroom, kitchen, laundry room, or closet.
- Place the detector at breathing height — about 0.8 to 2 m above the floor (roughly knee-to-head height), where the air you actually breathe is.
- Keep it clear of walls, the ceiling, and other objects — about 40 cm from interior walls, ~50 cm from exterior walls, at least ~50 cm below the ceiling, and ~20 cm from other items. A shelf or table works well.
- Keep it away from drafts, vents, exterior walls, windows, heat, direct sun, and high humidity — all of these can skew the reading.
- Don't put it inside a cabinet, drawer, or closet, and don't seal it in any enclosed space.
- Leave it undisturbed for the full test — at least 91 days — then return it to the lab promptly.
The short answer
Put a long-term radon detector in the lowest level of your home that you regularly live in, in a room you occupy at least four hours a day, at breathing height (about 0.8–2 m off the floor) and away from drafts, vents, windows, heat and direct sun — then leave it there, untouched, for at least 91 days. That's the placement Health Canada's measurement guide describes, and getting it right is what makes your result trustworthy.
Placement matters more than people expect. The same home can produce a meaningfully different number depending on where the detector sits, because radon concentrates near the soil-contact level and air currents from a nearby vent or open window can dilute the air around the device. The rules below aren't fussiness — they exist so your one result reflects the air your household actually breathes, not a draughty corner or a sealed cupboard.
Which level of the home
Test the lowest level of your home that you regularly use — the lowest "lived-in" level. Radon enters from the soil, so concentrations are usually highest on the floor closest to the ground. Health Canada's measurement guide directs you to measure in the lowest level you occupy, because that's where exposure is both highest and real.
What that means in practice:
- If you have a finished basement that you actually use — a rec room, a home office, a bedroom, a gym — that's where the decision is made. Test there.
- If your basement is unfinished, unused, or just for storage and the furnace, don't test there. Drop up to the lowest floor you genuinely live on — usually the main floor.
- If you don't have a basement at all (a slab-on-grade or crawl-space home), test the main floor — the lowest occupied level you have.
The principle is consistent: the test goes on the lowest level where someone spends real time, not the lowest level that exists. A storage cellar nobody sits in doesn't represent your exposure; the finished basement office where you work all week does. For why basements specifically tend to read high, see radon in basements in Canada.
Which room
Within that level, pick a room your household occupies at least four hours a day. The point of the test is to measure the air people actually breathe, so the room should be a normally lived-in space:
- Good choices: a bedroom, a living room, a family or rec room, or a home office — any room where someone genuinely spends several hours a day.
- Not these rooms: a bathroom, a kitchen, a laundry room, a closet, a crawl space, or any unfinished or unused space.
The excluded rooms are excluded for a reason. Bathrooms, kitchens, and laundry rooms have extra ventilation, humidity swings, and exhaust fans that move air in ways that don't reflect the rest of the home, so a detector there can read artificially low or behave unpredictably. Closets, crawl spaces, and unfinished areas aren't spaces anyone breathes in for hours, so they don't represent your real exposure — and an enclosed closet can trap stale air and distort the result the other way.
If the lowest lived-in level is a finished basement, the basement bedroom, office, or rec room is ideal. If it's the main floor, a main-floor bedroom or living room is the natural pick.
Exactly where in the room (height + clearances)
This is the part most people get wrong, and it's worth getting right. Health Canada's measurement guide gives specific clearances so the detector samples representative air:
- Height: about 0.8 to 2 m above the floor. That's the breathing zone — roughly knee-to-head height — where the air your household actually inhales sits. A shelf, a bookcase, a side table, or a dresser top all work well.
- Below the ceiling: at least about 50 cm. Don't tuck it up against the ceiling or on the top shelf jammed to the underside of a cabinet.
- From interior walls: about 40 cm. Give it space off the wall so it isn't sampling a stagnant pocket.
- From exterior walls: about 50 cm — a little more than from interior walls, because outside-facing walls are cooler and closer to air leakage.
- From other objects: at least about 20 cm. Don't crowd it against books, electronics, lamps, or clutter; it needs free air around it.
A simple way to satisfy all of this at once: set the detector on a shelf or table that's somewhere between waist and head height, out in the open, a couple of hand-widths off the wall, with clear air around it. Don't hang it from the ceiling, don't sit it on the floor, and don't bury it behind things on a crowded shelf.
What to keep it away from
Air movement and environmental extremes are the enemy of a clean reading. Keep the detector away from:
- Drafts and air currents of any kind — these dilute the air around the device and pull the reading down.
- HVAC vents and fans — supply registers, cold-air returns, and any fan. Forced air sweeping past the detector doesn't reflect the room's true radon level.
- Exterior doors and windows — both because they leak outdoor air and because they're a source of drafts.
- Heat sources and direct sunlight — radiators, baseboard heaters, fireplaces, sunny windowsills. Heat and direct sun can affect the detector and the air around it.
- High humidity — another reason bathrooms, laundry rooms, and damp corners are poor choices.
- Enclosed spaces — do not put the detector inside a cabinet, drawer, cupboard, or closed box. It needs to sit in the open air of the room.
If you can feel a draft, hear a fan, or feel sun warmth where you're thinking of placing it, choose a calmer spot on the same level instead.
Leave it alone for the full test
Once the detector is placed, the most important thing you can do is nothing.
- Don't move it, cover it, or relocate it partway through. A long-term alpha-track detector records a cumulative measurement over the whole period, so disturbing it mid-test compromises the result.
- Don't change how you live for the detector's sake. Don't seal the house up unnaturally, and equally don't throw windows open more than you normally would. Live normally — the test is meant to capture your real, everyday conditions.
- Leave it in place for the full duration — at least 91 days (about three months). Ninety-one days is the minimum valid measurement period for a long-term test under Health Canada's guidance; many people run it longer, up to a year.
- When the test is done, return it to the lab promptly using the prepaid return shipping, so analysis isn't delayed.
A long-term test is a "set it and forget it" exercise on purpose: the whole reason it's accurate is that it averages out radon's daily and seasonal swings, and that only works if you let it run undisturbed. (Why long-term rather than a quick test? See short-term vs long-term radon test in Canada.)
One kit per area — and where to test if you have no basement
For a typical single-family home, one detector placed correctly on the lowest lived-in level is what Health Canada's guidance is built around. It represents the level where exposure is highest and where people spend their time. (Larger or multi-unit buildings, or homes with separate living areas on different levels, can warrant more than one — but for most houses, one well-placed detector on the lowest lived-in level is the measurement that matters.)
No basement? Test the main floor. If your home is built on a slab or over a crawl space and has no basement, the rule doesn't change — you simply measure the lowest level you live on, which is the main floor. Place it in a main-floor bedroom, living room, or office, following the same height and clearance rules above. A slab-on-grade home is still in direct contact with the soil, so it can absolutely have elevated radon; not having a basement is never a reason to skip testing.
If you're weighing where in the house to test or which type of test to run, our guides on radon in basements in Canada and short-term vs long-term radon testing cover the details.
Frequently asked questions
Where should I put my radon test kit? On the lowest level of your home that you regularly live in, in a room you occupy at least four hours a day, at breathing height (about 0.8–2 m off the floor) on a shelf or table, away from drafts, vents, windows, heat, direct sun, and high humidity. Then leave it undisturbed for at least 91 days.
Which room is best? A room you actually use for several hours a day — a bedroom, living room, rec room, or home office. Avoid bathrooms, kitchens, laundry rooms, closets, crawl spaces, and unfinished or unused spaces, because their ventilation, humidity, and exhaust fans don't reflect the air the rest of your home breathes.
How high off the floor should the detector be? About 0.8 to 2 m above the floor — roughly knee-to-head height, the "breathing zone." Keep it at least ~50 cm below the ceiling, about 40 cm from interior walls (~50 cm from exterior walls), and at least ~20 cm from other objects. A shelf or table at waist-to-head height is ideal.
Can I test in the basement if I don't use it? No. Test the lowest level you actually live in. If the basement is unfinished, unused, or just for storage and the furnace, move up to the lowest occupied floor — usually the main floor. If the basement is finished and you spend time there (office, rec room, bedroom), then yes, test there.
Can I open windows during the test? Live normally — don't change your habits for the detector. Don't deliberately seal the house up, and don't deliberately air it out more than usual either, because both distort the result. The detector should also be kept away from windows, since they're a source of drafts and outdoor air.
What if I have no basement? Test the main floor — the lowest level you live on. Slab-on-grade and crawl-space homes sit right on the soil and can have elevated radon too, so place the detector in a main-floor bedroom, living room, or office following the same height and clearance rules. Not having a basement is never a reason to skip testing.
Does placement affect accuracy? Yes. Where you put the detector genuinely changes the result. A device set on the floor, jammed against a wall, sealed in a cabinet, or sitting next to a vent, window, or heat source can read inaccurately. Following Health Canada's height and clearance rules — breathing height, in the open, on the lowest lived-in level, away from air currents — is what makes your one result trustworthy.
How long do I leave it in place? At least 91 days (about three months) for a long-term test, undisturbed the whole time, then return it to the lab promptly. Ninety-one days is the minimum valid measurement period under Health Canada's guidance. See short-term vs long-term radon test in Canada.
Test your home the way Health Canada recommends
Placement is simple once you know the rules: lowest lived-in level, a room you use 4+ hours a day, at breathing height on a shelf or table, away from drafts, vents, windows, heat and sun — then leave it alone for at least 91 days.
Order your RadonTest.ca kit → — a long-term alpha-track kit with placement guidance included, 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 (placement: lowest lived-in level; breathing-zone height of about 0.8–2 m; clearances from walls, ceiling and objects; rooms and conditions to avoid; long-term test of at least 91 days), modified 2025-12-22. https://radontest.ca/links/hc-measurements-guide
- Health Canada — Reducing radon levels in your home (testing and corrective-action guidance), modified 2025-10-09. https://radontest.ca/links/hc-mitigation-guide
- Take Action on Radon — Test for radon (long-term testing and placement guidance for Canadians), accessed June 2026. https://takeactiononradon.ca/test-for-radon/
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 and Take Action on Radon is summarized from the public sources listed above; confirm time-sensitive details with the responsible body.