Sources we use
- EPA Map of Radon Zones (EPA): county zones 1–3. A zone is a regional prediction of average indoor screening levels, never a result for an individual home.
- NH DHHS Radon Program data brief, July 2026 (PDF): statewide figures from 2007–2025 tests.
- NH DHHS Environmental Public Health Tracking, “Spotlight: Radon Risk,” Jan 2016 (PDF): county test counts, percent above 4.0 pCi/L and medians from 1988–2011 NH DES test data. This is the most recent county-level table we found; it is old, and we label it that way.
- American Lung Association, “Radon Testing Disparities: New Hampshire,” 2022 (PDF): smoothed county estimates from CDC data, 2008–2017. We only show the county figures the report states in its text.
- EPA and NH guidance on testing, results and mitigation: EPA Citizen's Guide, EPA Home Buyer's and Seller's Guide, NH DHHS Testing, NH DHHS Mitigation, NHDES radon in well water fact sheet.
How figures are labeled
Each number shows whether it is County or Statewide, plus its source, period, sample size when published, and the date we last checked the source. If a source doesn't publish something (for example a sample size), we say so. When county data isn't available, we say that plainly instead of applying statewide numbers to a county.
What gets indexed
We build pages for every county, but only publish pages for search when they have credible local sources and useful, distinct content. Right now that's New Hampshire. Other pages stay out of search until they meet that bar.
Updates
We recheck sources when agencies publish new data and at least every 6 months. Last full source check: October 31, 2026.