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How long does a radon test take?

By Radon411 Editorial TeamUpdated How we research

Short answer

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.

Next step: pick the right test for your home. Which test to use

Most people start with a short-term kit of a few days. Some devices have a longer minimum, such as a 7-day charcoal canister, and for a test of 2 to 4 days the house is closed for at least 12 hours before it starts and for the whole test.

A longer test gives a truer picture, because radon levels vary from day to day and season to season. A is more likely to show the year-round average, and if time permits it can confirm a short-term result.

What to do next: pick a for a first answer, follow its instructions for how long to leave it, and mail it the day it ends.

How long each kind of radon test runs

The length depends on the kind of test and on the device. Every radon test should run at least 48 hours. stay in the home from two days to 90 days, and stay more than 90 days. Within those bands the device sets the time: some, such as a 7-day charcoal canister, have a longer minimum, so the exact length is whatever the kit's instructions say.

Table comparing a short-term radon test, a long-term radon test and a continuous radon monitor: how long each runs and what each is for.
Read this figure as text
TestHow long it runsWhat it is for
Short-term testStays 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 testStays 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 monitorLogs 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.
Short-term tests, long-term tests and continuous monitors, and how long each stays in the home.
Typical test lengths
TestHow long it runsTypical devices
Short-term, 2 to 4 daysAt least 48 hours; the house is closed 12 hours before and throughoutCharcoal canisters, charcoal liquid scintillation, electret ion chambers, continuous monitors
Short-term, 4 to 7 daysClosed-house conditions kept for the whole testSome charcoal canisters have a 7-day minimum
Short-term, up to 90 daysUp to 90 days, depending on the deviceAlpha track and electret detectors
Long-termMore than 90 daysAlpha track and electret detectors

Why a longer test tells you more

Radon levels move. They vary from day to day and season to season, and within a building even from hour to hour; rain or snow, barometric pressure and other influences push them up and down. A short test catches a slice of that, so it is less likely than a long-term test to show the year-round average. The longer the test, the better the result reflects the home and how you live in it, and a measurement of at least three months is the better estimate of a home's annual mean.

The trade between speed and certainty
If you needChooseWhy
An answer quicklyA short-term testIt is the quickest way to test, and a short-term result can be used to decide whether to fix
The year-round averageA long-term testA long-term result is more likely to reflect the home's year-round level
BothShort-term first, then long-termIf time permits, a long-term test can confirm an initial short-term result

From the end of the test to a result

  1. Record the times

    Write down the start and stop dates and times; the lab needs them.

  2. Mail it right away

    Reseal the package and send it to the lab named on it as soon as the test ends.

  3. Wait for the lab

    Results usually come back within a few days or weeks. If you are in a hurry, ask how long results take and whether expedited service is available.

  4. Or use a monitor

    A continuous monitor measures and records radon as it goes, and a qualified tester can explain its report.

How long tests take in a home sale and after a fix

Real estate testing is built around the deadline of a sale, so it uses short-term tests of at least 48 hours, in one of three ways.

EPA's three short-term radon testing options for a real estate transaction: two tests at the same time, one test then a second, or a continuous monitor, each for at least 48 hours, with what to do after each.
Read this figure as text

If you are testing in a real estate transaction and you need results quickly, any of the following three options for short-term tests are acceptable in determining whether the home should be fixed.

  1. Option 1. Two tests at the same time

    Passive

    Take two short-term tests at the same time in the same location for at least 48 hours.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    Two tests taken at the same time (simultaneous) would improve the precision of this radon test.

  2. Option 2. One test, then a second

    Passive

    Take an initial short-term test for at least 48 hours. Immediately upon completing the first test, do a second test using an identical device in the same location as the first test.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    One test followed by another test (sequential) would most likely give a better representation of the seasonal average.

  3. Option 3. A continuous monitor

    Active

    Test the home with a continuous monitor for at least 48 hours.

    What to do nextFix the home if the average radon level is 4 pCi/L or more.

    Both active and passive devices may have features which help to prevent test interference.

Any real estate test for radon should include steps to prevent or detect interference with the test device. Your state radon office can help you decide which option is best.

The three short-term testing options for a home sale, each running at least 48 hours.

After a system is installed, the check is a two- to seven-day measurement, taken within 30 days of installation but no sooner than 24 hours after the system starts running with the fan on. See how long after radon mitigation you can retest.

Questions about how long radon tests take

Can a radon test be done in a day?

No. Every radon test should run at least 48 hours, and some devices need longer.

Is a 2-day radon test enough?

A test of at least 48 hours gives a usable short-term result, and a high one is confirmed with a second test. Tests of just 2 or 3 days should not be run during unusually severe storms or high winds.

How long do radon test results take?

From a lab, usually a few days or weeks after you mail the device. A continuous monitor records as it goes, and the tester analyzes the data and reports the result.

How long is a long-term radon test?

More than 90 days. A test of at least three months is the better estimate of the year-round average.

How long does a radon test take during a home inspection?

At least 48 hours, with one of the three real estate options: two tests side by side, one test followed by another, or a continuous monitor. See should I get a radon test with my home inspection.

Can I leave a short-term test out longer than the instructions say?

Follow the package: leave it in place for as long as it says, record the stop time and mail it right away. For a longer measurement, use a long-term test, which runs more than 90 days.

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