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Radon Levels in Carroll County, New Hampshire

EPA puts Carroll County in Zone 1, its highest radon zone, and high results are common there: 54.0% of the 161 radon tests reported to CDC (2021) came back at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    54.0%

    11.3 pts above NH

    Carroll
    54.0%
    NH
    42.7%

    161 tests, 2021

  • Median result

    4.3pCi/L

    Action level reached

    Carroll
    4.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2021

  • Tests reported

    161

    5th of 10 by tests

    Carroll
    161
    Rockingham
    638

    Reported to CDC before any fix, 2021

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in NH

    1 of 10

    Top quarter

    Carroll
    54.0%
    Carroll
    54.0%

    By share, of 10 with 30+ tests

Read a result for Carroll County

Starts at Carroll County's median, 4.3 pCi/L

4.3pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 4.3 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Carroll County's median reported result, 2021.

Interpret this readingWhat a fix costs

The data

Carroll County, At a glance

Carroll County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Carroll County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 46% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Carroll County, 2021

Share of reported tests at or above 4 pCi/L, by year, Carroll County
Share of reported tests at or above 4 pCi/L, by year, Carroll County
YearShare of reported tests at or above 4 pCi/L
201848.5%
201954.2%
202052.3%
202154.0%

2021: 54.0%. Across these years the share ran from 48.5% to 54.2%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 161 tests reported to CDC for Carroll County over 2021, many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2021. Measured data period: 2005 to 2021 (every CDC figure on file).

How to read these figures

Carroll County, Compared

Carroll County radon figures, compared

Calculated by Radon411

More than half: 54.0% of the 161 radon tests reported to CDC for Carroll County in 2021 read at least 4 pCi/L. That places it 1st of 10 New Hampshire counties with 30 or more tests for the same period. That is 11.3 points above the 42.7% pooled from 10 New Hampshire counties.

The median result, 4.3 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 345.3 pCi/L. The rest split 18.6% under 2 pCi/L and 27.3% from 2 to 4 (New Hampshire: 32.3% and 25.0%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 54.0% share point the same way here.

No bordering county with a figure for the same period reported a higher share; the closest is Coos County at 52.3%, the lowest Belknap County at 36.3%. Statewide for the same period, Coos County reported the highest share (52.3%) and Cheshire County the lowest (19.4%).

The busiest year on file was 2019, with 201 tests reported; the quietest, 2018, had 134.

Over 4 years of annual figures the share rose 5.5 points, from 48.5% in 2018 to 54.0% in 2021; its peak was 54.2% in 2019. Nationally, every county with a figure for the same period pools to 24.4%; Carroll County sits 29.6 points above it. CDC also counts 60 tests taken after mitigation in Carroll County for the same period: tests in homes where a fix was already in.

Share of reported tests at or above 4 pCi/L by year, Carroll County against New Hampshire2018 to 2021, years with 30 or more tests: Carroll County 48.5% to 54.0%, the state's pooled share 42.7% in 2021.
Carroll CountyNew Hampshire, pooled
Share of reported tests at or above 4 pCi/L by year, Carroll County against New Hampshire: data table
YearTestsCarroll County, at or above 4 pCi/LNew Hampshire, pooled
201813448.5%34.6%
201920154.2%40.6%
202015352.3%40.2%
202116154.0%42.7%
Carroll County against New Hampshire, the United States and nearby counties, 2021
AreaTestsAt or above 4 pCi/LMedianDifference from Carroll County
Carroll County16154.0%4.3 pCi/LThis county
New Hampshire, pooled10 counties, pooled2,26042.7%Not pooled−11.3 points
United States, pooled807 counties, pooled344,60424.4%Not pooled−29.6 points
Rockingham Countyhighest in the state63848.1%3.7 pCi/L−5.9 points
Cheshire Countylowest in the state10319.4%2.1 pCi/L−34.6 points
Coos County, NHborders it4452.3%4.3 pCi/L−1.7 points
Strafford County, NHborders it21347.9%3.6 pCi/L−6.1 points
Grafton County, NHborders it14244.4%3.0 pCi/L−9.6 points
Belknap County, NHborders it10236.3%2.6 pCi/L−17.7 points
Where Carroll County's reported results fell, 2021, beside New Hampshire and the United States
ResultCarroll County testsCarroll County shareNew Hampshire shareU.S. shareAgainst New Hampshire
Under 2 pCi/L3018.6%32.3%54.4%−13.7 points
2 to 4 pCi/L4427.3%25.0%21.2%+2.3 points
4 pCi/L and above8754.0%42.7%24.4%+11.3 points
Carroll County ranked among the 10 New Hampshire counties with 30 or more tests, by share at or above 4 pCi/L, 2021
CountyRankTestsAt or above 4 pCi/LMedian
Carroll County1 of 1016154.0%4.3 pCi/L
Coos County2 of 104452.3%4.3 pCi/L
Rockingham County3 of 1063848.1%3.7 pCi/L
Strafford County4 of 1021347.9%3.6 pCi/L
Grafton County5 of 1014244.4%3.0 pCi/L
Hillsborough County6 of 1061041.5%3.2 pCi/L
Belknap County7 of 1010236.3%2.6 pCi/L
Merrimack County8 of 1018731.6%2.2 pCi/L
Sullivan County9 of 106023.3%2.7 pCi/L
Cheshire County10 of 1010319.4%2.1 pCi/L
Carroll County radon tests by year, against New Hampshire's pooled share
YearTestsAt or above 4 pCi/LMedianHighestNew Hampshire, pooledChange from the row before
202116154.0%4.3 pCi/L345.3 pCi/L42.7%+1.7 points
202015352.3%4.1 pCi/L417.9 pCi/L40.2%−1.9 points
201920154.2%4.2 pCi/L214.9 pCi/L40.6%+5.7 points
201813448.5%3.9 pCi/L73.7 pCi/L34.6%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Carroll County, Geology

The ground under Carroll County

Predicted

No class of ground holds half of Carroll County on USGS's geologic map: 45.9% of its land is high radon potential, 38.0% moderate and 16.2% low. The map puts 24.8% of Carroll County in the area it calls White Mountains and 20.6% in Ossipee Mountains/Central Lowlands, with 7 smaller areas beside them. USGS gives both a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Carroll County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
White MountainsJurassic-Cretaceous rocks of the White Mountain and New England-Quebec igneous succession.High1324.8%
Ossipee Mountains/Central LowlandsSilurian-Devonian intrusive rocks ranging from gabbro to granite.High1320.6%
Parts of Central Lowlands, Eastern New England Upland and Merrimack ValleyPhyllite, calcareous and aluminous schist, quartzite, slate, granofels, metavolcanic rocks.Moderate1016.9%
Central LowlandsSilurian-Devonian intrusive rocks ranging from gabbro to granite.Low816.2%
White MountainsDevonian-Carboniferous two-mica granite.Moderate107.8%
White MountainsCambrian-Devonian schist, slate, quartzite, metavolcanic rocks, granite.Moderate107.3%

3 smaller areas are not listed. Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Carroll County beside the ground around it

Carroll County has more high-potential ground than New Hampshire as a whole: 45.9% of its land against 18.8%. Of the 6 counties that border it, 2 have more high-potential ground, York County, ME the most at 99.1%.

Share of land by USGS radon potential: Carroll County, the 6 counties bordering it and New Hampshire
AreaEPA zoneLow potentialModerate potentialHigh potential
Carroll CountyZone 116.2%38.0%45.9%
Belknap CountyZone 217.7%71.8%10.5%
Grafton CountyZone 23.5%78.8%17.7%
Strafford CountyZone 20.1%73.6%25.5%
York County, MEZone 1None0.1%99.1%
Oxford County, MEZone 1None14.9%85.1%
Coos CountyZone 2None83.7%16.3%
New Hampshire10 counties, pooled by land areaVaries9.6%71.4%18.8%

The map rates the ground, not the air in any home.

Local help

Carroll County, Local resources

Radon testing and mitigation in Carroll County

What New Hampshire's program says
Licensing of radon professionals
There is no requirement in New Hampshire for those professionals testing for radon to be certified but it is recommended to use a nationally certified radon measurement professional especially if a real estate transaction is involved.

What it means

Carroll County, Questions

Questions about radon in Carroll County

Are radon levels high in Carroll County?

In 2021, 54.0% of the radon tests reported to CDC for Carroll County, New Hampshire were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.3 pCi/L. Of 10 New Hampshire counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 42.7%.

Which counties border Carroll County?

Carroll County borders 6 counties: Belknap County, NH, Grafton County, NH, Strafford County, NH, York County, ME, Oxford County, ME and Coos County, NH.

Products

Carroll County, Products

Testing a home in Carroll County

In Carroll County, 54.0% of 161 tests reported to CDC in 2021 reached 4 pCi/L, against 42.7% pooled across New Hampshire. In Zone 1 the year-round level in Carroll County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.

Test kits and monitors3

See every kit and monitor

Carroll County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Carroll County

Explore

Carroll County, Bordering counties

Counties bordering Carroll County

Calculated by Radon411

Carroll County, Residents

Who lives in Carroll County

Carroll County is growing: the Census Bureau puts it at 52,784 residents on July 1, 2025, up 5.0% from 50,251 in 2020. That works out to 57 people per square mile of land. Testing is reported here more often than across the state: CDC's 161 reported tests for 2021 come to 3.1 for every 1,000 residents (2025 estimate), against 1.6 for New Hampshire.

Census lists no incorporated place in Carroll County: every home in it reads the county's figures.

Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).

Carroll County, Homes

Homes in Carroll County

Carroll County is a place of houses on their own lots: 77% of its 40,110 homes are detached single-family houses, against 63% across New Hampshire. Half of its homes were built before 1981, close to New Hampshire's 1978: 24% date from before 1960 and 20% from 2000 or later. Owners live in 81% of the occupied homes (New Hampshire: 73%), so for most households a test and a fix are their own to order.

Homes in Carroll County, New Hampshire, 2019 to 2023
HomesCarroll CountyNew Hampshire
Housing units40,110644,253
Detached houses77%63%
In buildings of 5 or more8%15%
Mobile homes6%5%
Built before 196024%29%
Built since 200020%18%
Middle year built19811978
Owner-occupied81%73%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.