How to read a radon test result (pCi/L)
What your radon number means and what EPA and New Hampshire recommend next.
Radon test results in the U.S. are reported in picocuries per liter of air (pCi/L). The national average indoor level is about 1.3 pCi/L; NH DHHS estimates New Hampshire's at 5.9 pCi/L. Outdoor air averages about 0.4 pCi/L, so no home reaches zero.
| Result | What guidance says |
|---|---|
| Below 2 pCi/L | Lower risk, but no level is known to be safe. NH DPH recommends retesting at least every 2 years and after construction. |
| 2 to 3.9 pCi/L | EPA says consider fixing your home. |
| 4 pCi/L or higher | EPA's action level: EPA recommends fixing your home. If it was a short-term test, confirm with a follow-up test first. |
Confirming a high result
EPA's Citizen's Guide says that if a short-term result is 4 pCi/L or higher, you should do a follow-up test: a long-term test for a better yearly average, or a second short-term test if you need results quickly. Fix the home if the long-term result is 4 pCi/L or more; if you used two short-term tests, EPA says consider fixing if their average is 4 pCi/L or higher. If the first short-term result is more than 8 pCi/L, EPA says take the second short-term test immediately.
Why results vary
Radon changes day to day and season to season. NH DHHS notes it tends to be higher in colder months when homes are heated and closed up, so a summer result may read lower than a winter one.
In New Hampshire? Order a free state test kit or see radon by NH county.
More guides
- Short-term vs long-term radon tests
- Radon testing when buying or selling a home in NH
- Radon in well water in New Hampshire
- Radon mitigation basics
- When to retest for radon
Sources
- EPA, A Citizen's Guide to Radon
- NH DHHS Radon Program data brief, July 2026
- NH DHHS, Testing for Radon
- NH DHHS, Fixing Radon: Mitigation
Sources checked October 31, 2026. Spot an error? Send a correction.