How Long Does a Radon Test Take?

A radon test takes anywhere from 48 hours to more than 90 days, depending on the type you use. Short-term tests stay in your home for 2 to 90 days — many do-it-yourself charcoal kits run for just a few days — while long-term tests run for more than 90 days. If you mail the kit to a lab, add shipping and analysis time: the EPA says to expect results within a few days or weeks.

This guide follows U.S. EPA guidance and its action level of 4 pCi/L (148 Bq/m³). Other countries use different reference levels and testing rules, so check your national or local guidance if you live outside the United States.

How long each type of radon test takes

The minimum matters: the EPA says all radon tests should be taken for at least 48 hours, whether you test yourself or hire a qualified tester. Your kit’s instructions give the exact exposure time for that device — leave it in place for as long as the package says, and record the start and stop dates and times.

For help choosing between them, see Short-Term vs Long-Term Radon Testing.

A typical short-term test timeline

For a short-term kit that you mail to a lab, the whole process looks like this:

1. 12 hours before the test (tests shorter than four days): close your windows and outside doors.
2. During the test: keep closed-house conditions for the full exposure time on the package — at least 48 hours.
3. When the test ends: record the stop time, reseal the kit and mail it to the lab right away.
4. Results: expect them within a few days or weeks, depending on shipping and the lab. If you are on a deadline, ask the lab about turnaround and expedited service before you start.

For step-by-step setup and placement, see How to Test for Radon and Where to Put a Radon Detector.

Closed-house conditions: before and during the test

Short-term tests are only reliable if the house stays closed. The EPA defines closed-house conditions as keeping all windows closed, keeping doors closed except for normal entry and exit, and not running fans or other machines that bring in air from outside. Fans that are part of a radon-reduction system, and small exhaust fans run only for short periods, may operate.

The EPA advises keeping closed-house conditions for the entire short-term test, especially for tests shorter than one week. What changes with the length of the test is the preparation:

Your test device, your tester or local rules may set stricter requirements — follow them where they differ.

Run your heating and cooling normally; systems that recirculate indoor air can run. Don’t run a short-term test lasting less than four days during severe storms or periods of high winds.

Why longer tests give a better picture

Radon levels tend to vary from day to day and season to season. A short-term test is a snapshot of those few days, so it is less likely than a long-term test to tell you your year-round average. A long-term test, running for more than 90 days, averages out more of that variation.

That difference shapes the EPA’s testing steps:

1. Start with a short-term test. If the result is 4 pCi/L (148 Bq/m³) or higher, take a follow-up test to be sure.
2. Follow up with either a long-term test or, if you need results quickly, a second short-term test. The higher the first result, the more reason to choose a short-term follow-up — and if it is more than twice the action level, above 8 pCi/L (296 Bq/m³), take a second short-term test immediately rather than waiting more than 90 days for a long-term result.
3. Decide: fix your home if the long-term result is 4 pCi/L (148 Bq/m³) or higher, or if the average of the two short-term tests is 4 pCi/L (148 Bq/m³) or higher.

So if your first short-term result is high, build in time for the follow-up — a few more days for a second short-term test, or more than 90 days for a long-term test.

How long a radon test takes for a home sale

In a real-estate transaction, timing is usually tight. The EPA lists three short-term options, and the total time depends on which one you choose:

Add the 12 hours of closing up before a test shorter than four days, plus shipping, lab analysis and report delivery. Agree on when the report will be delivered before you schedule the test, so it fits your contract deadlines. See Radon Test for Home Inspection for the full process.

Testing again after mitigation

If you fix your home, test again to confirm the level has come down. The EPA says a post-mitigation test should be done within 30 days of system installation, but no sooner than 24 hours after the system is running with its fan on, and recommends a two- to seven-day measurement. It also recommends that this test be done by an independent, qualified radon tester (or by you), not only by the contractor who installed the system. After that, it’s a good idea to retest every two years to make sure levels stay low, and again if you start using a lower level of your home or after major renovations.