Radon in New Hampshire
About 3 in 10 homes tested in New Hampshire were at or above the EPA action level of 4 pCi/L.
- Below 2 pCi/L: 41%
- 2 to 4 pCi/L: 24%
- 4 pCi/L or more: 35%
The EPA puts 1 of New Hampshire's 10 counties in Zone 1, its highest radon category, 9 in Zone 2 and 0 in Zone 3.
Every county in New Hampshire
Sorted by the share of homes tested at or above 4 pCi/L. Select a county for local details and costs.
| County | Homes tested | At or above 4 | Median | EPA zone |
|---|---|---|---|---|
| Carroll County | 48% | 3.5 pCi/L | 1 | |
| Strafford County | 43% | 3.1 pCi/L | 2 | |
| Rockingham County | 42% | 3.1 pCi/L | 2 | |
| Hillsborough County | 34% | 2.5 pCi/L | 2 | |
| Coos County | 34% | 2.3 pCi/L | 2 | |
| Belknap County | 32% | 2.3 pCi/L | 2 | |
| Merrimack County | 31% | 2.1 pCi/L | 2 | |
| Grafton County | 26% | 2.2 pCi/L | 2 | |
| Sullivan County | 25% | 2.3 pCi/L | 2 | |
| Cheshire County | 20% | 1.8 pCi/L | 2 |
"–" means fewer than 20 tests or no lab data, too few for a reliable figure.
Sources
- EPA Map of Radon Zones (public domain).
- CDC Environmental Public Health Tracking Network, radon tests from labs, 2008–2017. Pre-mitigation tests only.
Last updated October 2026. How we calculate these numbers.