Radon in New Hampshire: radon map by county

EPA's Map of Radon Zones puts 1 of New Hampshire's 10 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 9 in Zone 2 and 0 in Zone 3. Of 10,471 building tests that radon laboratories reported for 2008 to 2017, 34.9% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 19 of 42 states with 1,000+ tests). The highest county share is Carroll County (48.2% of 324 tests).

counties in Zone 1 (above 4 pCi/L predicted)

counties in Zone 2 (2 to 4)

counties in Zone 3 (below 2)

34.9%

of 10,471 lab tests at or above 4 pCi/L

Radon by county in New Hampshire

EPA radon zone and radon test results for each county in New Hampshire
County	EPA zone	Lab tests	Median	4+ pCi/L
Belknap County	Zone 2	285	2.3	32.2%
Carroll County	Zone 1	324	3.5	48.2%
Cheshire County	Zone 2	600	1.8	20.4%
Coos County	Zone 2	227	2.3	33.7%
Grafton County	Zone 2	1,207	2.2	25.9%
Hillsborough County	Zone 2	3,558	2.5	34.4%
Merrimack County	Zone 2	884	2.1	31.4%
Rockingham County	Zone 2	2,535	3.1	41.9%
Strafford County	Zone 2	648	3.1	42.5%
Sullivan County	Zone 2	203	2.3	25.1%

Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).

What the zones mean

Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.

Radon in New Hampshire: questions

What radon zone is New Hampshire?

EPA's 1993 map does not give states one zone; it zones each county. In New Hampshire, 1 county is Zone 1, 9 Zone 2 and 0 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".

Which New Hampshire counties have the highest radon levels?

By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Carroll County 48.2% (median 3.5 pCi/L, 324 tests); Strafford County 42.5% (median 3.1 pCi/L, 648 tests); Rockingham County 41.9% (median 3.1 pCi/L, 2,535 tests); Hillsborough County 34.4% (median 2.5 pCi/L, 3,558 tests); Coos County 33.7% (median 2.3 pCi/L, 227 tests).

How common is high radon in New Hampshire?

34.9% of the 10,471 tests in the laboratory data for New Hampshire (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.

Does New Hampshire publish its own radon test data?

New Hampshire's radon program reports county test results; the latest year with county results is 2021, shown on each county page.

Should I test for radon in New Hampshire?

Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.

States bordering New Hampshire

Radon in Maine (12 of 16 in Zone 1)Radon in Massachusetts (3 of 14 in Zone 1)Radon in Vermont (0 of 14 in Zone 1)

Other free hazard lookups

All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).

Superfund sites in New Hampshire · Radon map of every state

Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.