Short-Term vs Long-Term Radon Tests

How the two kinds of radon tests differ, and the EPA's step-by-step guidance on what to do with your result.

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Short-term: 2–90 days

Quickest way to test. Common devices: charcoal canisters, alpha track, electret ion chambers, continuous monitors and charcoal liquid scintillation. Because radon varies day to day and season to season, less likely to show your year-round average.

Long-term: more than 90 days

Usually alpha track or electret detectors. More likely to show your home's year-round average radon level.

Source: EPA, A Citizen's Guide to Radon.

EPA's recommended testing steps

  1. Take a short-term test. If the result is 4 pCi/L or higher, take a follow-up test to be sure.
  2. Follow up with a long-term test for a better understanding of your year-round average, or a second short-term test if you need results quickly. If your first result is more than twice the 4 pCi/L action level, take a second short-term test immediately.
  3. Decide. Fix your home if a long-term result is 4 pCi/L or more. With two short-term tests, consider fixing your home if their average is 4 pCi/L or higher.

For 2–3 day tests, the EPA says to close windows and outside doors at least 12 hours before starting, and not to test during unusually severe storms or high winds.

Buying or selling?

Real estate timelines usually call for short-term testing. See radon testing during a home sale. Need a certified tester or a mitigation quote? Use the form above.

FAQ

How long is a short-term radon test?

The EPA says short-term tests stay in your home for 2 to 90 days, depending on the device.

How long is a long-term radon test?

More than 90 days. The EPA says a long-term test is more likely than a short-term test to tell you your home's year-round average radon level.

My short-term test was over 4 pCi/L. Now what?

The EPA recommends a follow-up test: a long-term test for a better picture of your year-round average, or a second short-term test if you need results quickly. If your first result is more than twice the 4 pCi/L action level, the EPA says to take a second short-term test immediately.