Radon Compass

How we know

Every number on Radon Compass comes from a public source, shown on the page where it's used. Here's where the data comes from, how we calculate the figures, and what they can't tell you.

Sources

  • Radon test results by county come from the CDC's Environmental Public Health Tracking Network: tests reported by national radon testing laboratories, 2008–2017, pre-mitigation tests only. That covers 46 states and DC. Kansas, New Jersey, Hawaii and Mississippi aren't included.
  • Pennsylvania zip codes and costs come from the Pennsylvania Department of Environmental Protection, which collects every certified radon test and mitigation in the state. Test results run from October 2016 to the latest month; costs are from installs since 2021.
  • Radon zones come from the EPA Map of Radon Zones, a 1993 model based on geology, soil and early indoor measurements.

How we calculate the figures

  • The band shows the share of homes tested below 2 pCi/L, between 2 and 4, and at or above 4, the level at which the EPA recommends fixing a home.
  • Median level is the middle test result: half of the homes tested were higher, half lower. For Pennsylvania zip codes it's estimated from results grouped in 0.5 pCi/L steps. Where we combine zip codes into a county, we show a typical level weighted by the number of tests.
  • Costs are the middle half of reported installation prices for new standard systems: a quarter of homes paid less than the low figure, a quarter paid more than the high one. Activating or modifying an existing system is excluded, as are prices below $300 or above $10,000.
  • Small samples: with fewer than 20 tests, we show the number of tests but not percentages.

What the numbers can't tell you

  • Your home's level. Neighboring houses can differ a lot, so the only way to know is to test.
  • Whether an area is safe. High radon has been found in every EPA zone.
  • Exactly who tests. People in areas known for radon test more often, and home sales drive many tests, so results aren't a random sample of all homes.
  • For Pennsylvania zip codes, whether a test was taken before or after mitigation. The state records don't say, so some tests in those figures are from homes that were already fixed.