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Long-term radon test kits: measuring your year-round average
Short answer
A long-term radon test stays in your home for more than 90 days, usually with an alpha track or electret detector, and gives a result more likely to reflect your year-round average than a short-term test. Run it through the heating season and live normally while it runs.
Key takeaways
- A long-term test stays in your home for more than 90 days, usually 3 months to 1 year.
- Its result is more likely to tell you your home's year-round average than a short-term test.
- Alpha track and electret detectors are the devices commonly used. An alpha track detector usually runs 100 to 120 days.
- No closed-house rules: you live in the home as you normally do while it runs.
- Run it through the heating season. Canada's guidance asks for at least 91 days of the test to fall in it.
What a long-term radon test is
A long-term radon test measures the radon in your home over months rather than days. The definition is simple: it stays in the home for more than 90 days, usually 3 months to 1 year. Because it spans the seasons, its reading is more likely to tell you your home's year-round average than a , and it gives a better average of the radon you actually breathe.
That year-round average is what radon risk is about, which is why some programs ask for it before any decision. Health Canada defines a as at least 91 days and recommends basing decisions on a fix on tests of at least that length. In the United States, a long-term test confirms a short-term result when there is time, and stands on its own when you want the closest estimate of your average. The kinds of kit, and every kit we have verified, are on radon test kits.
- Long-term test
- Stays in the home for more than 90 days. It is more likely than a short-term test to tell you the home's year-round average radon level.
| Question | Answer |
|---|---|
| How long? | More than 90 days; usually 3 months to 1 year; at least 91 days in Canada |
| Which devices? | Alpha track and electret detectors; a continuous monitor run long enough also qualifies |
| House rules? | Live normally |
| Which season | Through the heating season, when levels are typically highest |
| What it tells you | A result more likely to reflect your year-round average |
The devices that do long-term testing
Alpha track and electret ion chamber detectors are the devices commonly used for long-term testing. Both are passive: they need no power and go to a laboratory or a qualified reader at the end.
| Device | How it works | Long-term use |
|---|---|---|
| Alpha track detector | A thin plastic film in a filtered chamber records tracks from alpha particles; a lab etches and counts them, and the count correlates with the integrated radon level | Usually 100 to 120 days; recommended in Canada for long-term tests |
| Electret ion chamber | Radiation from radon lowers the voltage on a charged disk; the drop over a known time is read with a calibrated reader | Short-term or long-term depending on the electret; long-term electrets are recommended in Canada |
| Continuous monitor run for months | Counts alpha particles continuously and reports averages | At least 3 months for a consumer monitor |
When to run a long-term test
Season matters more for a long test than for any other. Test preferably during the heating season, when indoor radon levels are typically highest. Canada's guidance is more precise: at least 91 days of the test should fall in the heating season, and a test with fewer may underestimate the average annual level and need a re-test.
| Point | What it means for your test |
|---|---|
| What the season does | Testing in the heating season will generally provide a conservative estimate of the annual radon level |
| Why levels rise | Reduced ventilation from closed windows and doors, and more radon entering from the soil through the stack effect |
| Starting at another time | Possible, but tests with fewer than 91 days in the heating season risk underestimating the annual average |
| If the test missed the season and read low | Re-test during the next heating season |
- To confirm a short-term result. If time permits (more than 90 days), a long-term test can confirm an initial short-term result.
- For your year-round average. As a follow-up, a long-term test gives a better understanding of your year-round average.
- After you change how you use the home. Retest if you begin occupying a lower level, such as a basement, or after renovating.
Running a long-term test
Choose the room
A room used regularly on the lowest lived-in level: a normal occupancy area where someone spends more than 4 hours a day. Not a kitchen, bathroom, laundry or storage room.
Place the device
Off the floor and away from an exterior wall, out of direct sunlight and away from air currents from vents, doors, fans and windows, where children and pets will not disturb it.
Record the start
Write the start date and the location on the form, as the instructions ask.
Live normally
Do not change how you live in the home during a long-term radon test. No closed-house conditions are needed.
End it on time
After the period on the instructions (usually 100 to 120 days for alpha track detectors), record the end date and seal the device.
Send it to the lab
Return it promptly with the form. Results come within a few days or weeks.
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| Test | How long it runs | What it is for |
|---|---|---|
| Short-term test | Stays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours. | A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average. |
| Long-term test | Stays in the home for more than 90 days. | It is more likely than a short-term test to tell you the home's year-round average radon level. |
| Continuous monitor | Logs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance. | Logs a graph over time, so you can see trends and spot anomalies rather than a single number. |
Reading a long-term result
A long-term result is the closest a single test gets to your year-round average, so it is a decision number. EPA recommends fixing a home when the radon level is 4 or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
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- Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
- 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
- At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
- Below 4 pCi/L: you may want to test again sometime in the future, and retest if you start using a lower level or renovate.
- Between 2 and 4 pCi/L: EPA recommends considering a fix.
- At or above 4 pCi/L: plan a fix; see radon mitigation. A home with a system should be retested at least every two years.
Long-term kit or radon monitor?
A consumer radon monitor run for more than 90 days is also a long-term measurement; run one for at least 3 months for that. The difference is what you see along the way: a kit gives one lab-read average at the end, while a monitor shows running averages throughout. Which suits you is covered in charcoal kit vs digital monitor, and every monitor with its independent evidence is on radon detectors and monitors.
| Compared | Long-term kit | Monitor run 3 months or more |
|---|---|---|
| What you get | One average from a laboratory | Running averages on a screen or app |
| Power | None | Battery or plug-in |
| Independent check | The laboratory that reads it | C-NRPP's consumer results, for models entered |
| Reuse | One test | Reusable |
Questions about long-term radon tests
How long is a long-term radon test?
More than 90 days. Most run 3 months to 1 year, and in Canada a long-term test means at least 91 days.
Is a long-term radon test more accurate?
It is more likely to reflect your year-round average, because it averages over more of the daily and seasonal changes in radon.
When should a long-term radon test run?
Through the heating season, when indoor levels are typically highest. Canada's guidance asks for at least 91 days of the test to fall in it.
Do I keep windows closed during a long-term test?
No. Live as you normally do during a long-term test.
What device is used for long-term radon testing?
Alpha track and electret ion chamber detectors are commonly used. A consumer monitor run for more than 90 days also gives a long-term average.
How long should an alpha track test stay out?
Usually 100 to 120 days. Follow the kit's own instructions and finish before its expiry date.
Should I do a long-term test after a high short-term test?
If you have time, yes: a long-term test can confirm an initial short-term result when more than 90 days is available. If you need to decide quickly, a second short-term test is the alternative.
Which long-term radon test kit should I buy?
We do not rank kits. Every long-term kit we have verified, with what its price covers, is on radon test kits.
What if my long-term test missed the heating season?
A test with fewer than 91 days in the heating season may underestimate the annual average; if it read low, re-test during the next heating season.
What do I do with a long-term result above 4 pCi/L?
EPA recommends fixing the home when long-term results are at or above 4 pCi/L. See radon mitigation.
Questions people ask
How long is a long-term radon test?
A radon test takes at least 48 hours. Short-term tests stay in the home from 2 to 90 days, depending on the device, and long-term tests more than 90 days; a lab result then comes back within a few days or weeks of mailing the device.
Must doors and windows stay closed for a long-term test?
Yes: you can live in the house as usual during a radon test, coming and going through the doors, running heating and air conditioning, and sleeping in the room with the device. Keep windows and outside doors closed, and do not run fans that bring in outside air or disturb the device.
Can I run a long-term radon test myself?
Yes. A do-it-yourself kit from a hardware store, online or by mail is the usual first test, and it takes only a few minutes of your time. Place it in the lowest lived-in level, keep the house closed, leave it for the time the kit says, at least 48 hours, then mail it to the lab.