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Licenses on file: see the profile
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Locations and reports
Radon in Danbury, Connecticut
EPA puts Fairfield County, where Danbury is, in Zone 1, its highest radon zone, and 33.4% of its 2,784 reported radon tests (2019) were 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
Share at 4+ pCi/L
33.4%
1.7 pts below CT
- Fairfield
- 33.4%
- CT
- 35.1%
Fairfield, 6th of 8 in CT, 2019
Median result
2.1pCi/L
Below action level
- Fairfield
- 2.1 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of Fairfield's tests, 2019
Nearest county
37.9%
New Haven, 28 miles
- New Haven
- 37.9%
- Fairfield
- 33.4%
1,007 tests, 2019
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
Fairfield, where Danbury is
Tests reported
2,784
In Fairfield
- Fairfield
- 2,784
- New Haven
- 1,007
Reported to CDC before any fix, 2019
Read a result for Danbury
Starts at Fairfield County's median, 2.1 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.1 pCi/L
Between 2 and 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Fairfield County's median reported result, 2019.
The data
Danbury, What is published
What is published for Danbury
Information:
Every figure for Danbury is a county's
Radon data is published by county, not by city, so for Danbury it is Fairfield County's: its EPA zone (Zone 1) and the 2,784 tests reported to CDC for 2019. Only a test tells you about one home.
Danbury covers 42 square miles of land, all of it in Fairfield County. About 89,033 people live there, 2,118 to the square mile.
Danbury, Counties
The county Danbury lies in
MeasuredFairfield County's EPA zone and the figures CDC publishes for it, 2019.
Fairfield CountyZone 1Highest predicted potential
- 33.4%
- Reported tests at or above 4 pCi/L
- 2.1 pCi/L
- Median reported result
- 2,784 tests
- Tests reported to CDC
- 6
- Annual years on file
Fairfield County ranks 6th of 8 Connecticut counties with 30 or more tests for that period, 1.7 points below the 35.1% pooled across Connecticut's counties, 4.4 points above the national pool of 29.0%.
Measured from the middle of Danbury, the nearest counties with a CDC figure for 2019 are New Haven County (28 miles, 37.9% of 1,007 tests), Litchfield County (29 miles, 33.8% of 346 tests) and Hartford County (47 miles, 31.5% of 606 tests). Across the 7 nearest, the share at or above 4 pCi/L runs from 29.4% to 48.5%; the farthest of them, Windham County, is 82 miles away at 39.4%.
The directory lists 2 businesses with an address in Danbury, 1 for testing and 2 for mitigation. Connecticut's other cities with a page of their own: Stamford.
The counties around Danbury
By distance from the middle of Danbury; counties with 30 or more tests.
Predicted: EPA Map of Radon Zones, by county. Measured: CDC tracking data, by county, 2019.
Danbury, Geology
The ground under Danbury
PredictedMost of the ground under Danbury is one class on USGS's geologic map: 93.4% of its land is moderate radon potential, with 6.6% high. The map puts 53.4% of Danbury in the area it calls Proterozoic massifs and 40.0% in Carbonate shelf, with one smaller area beside them. USGS gives the first a radon index of 10 and the second 9, both in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Proterozoic massifs | Gneiss, granitic gneiss, amphibolite, mica schist. | Moderate | 10 | 53.4% |
| Carbonate shelf | Marble and schist. | Moderate | 9 | 40.0% |
| Connecticut Valley Synclinorium | Schist, gneiss and phyllite. | High | 12 | 6.6% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Danbury beside its county and Connecticut
Fairfield County as a whole has more high-potential ground than Danbury: 79.5% of the county against 6.6% of the city. Connecticut as a whole has more high-potential ground than Danbury: 44.1% of its land, against 6.6% here.
The map rates the ground, not the air in any home.
Danbury, Homes
Homes in Danbury
Fewer than six in ten of Danbury's 34,798 homes are detached houses (42%, against 59% across Connecticut); the rest are attached, in shared buildings or mobile. Much of Danbury is recent building: 20% of its homes have gone up since 2000 and the middle year built is 1975, against 1967 for Connecticut. 55% of occupied homes are lived in by their owner (Connecticut: 66%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Danbury | Connecticut |
|---|---|---|
| Housing units | 34,798 | 1,536,049 |
| Detached houses | 42% | 59% |
| In buildings of 5 or more | 25% | 18% |
| Mobile homes | 1% | 1% |
| Built before 1960 | 30% | 41% |
| Built since 2000 | 20% | 12% |
| Middle year built | 1975 | 1967 |
| Owner-occupied | 55% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.
Local help
Danbury, Professionals
Radon professionals listed in Danbury
Businesses whose listed city is Danbury, from the state registries and listings in the Radon411 directory, with the same business and certification status the directory shows.
Radon professionals listed in Danbury: 1 of 2
2 listings with Danbury as the city. See radon mitigation and testing in Danbury, or all radon professionals in Connecticut.
Danbury, Local resources
Local resources for Danbury
Who to ask in Connecticut: its radon program, test kits and professionals.
- Radon ProgramRun by Department of Public Health, phone (860) 509-7300.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
A part of the partnership includes providing LHDs free short-term radon in air test kits for distribution to community residents.
- Compare kits
- Professionals in Connecticut2 listings cover Danbury.
The program's own words on licensing are on the Connecticut page.
What it means
Danbury, Questions
Questions about radon in Danbury
What radon zone is Danbury in?
EPA's map puts Fairfield County, and with it Danbury, in Zone 1, the map's highest class: a predicted county average above 4 pCi/L.
What are radon levels in Danbury?
Around Danbury, 33.4% of 2,784 tests reported from Fairfield County for 2019 reached 4 pCi/L or more, so a high result is no surprise here. The median reported result was 2.1 pCi/L.
Should I test my home in Danbury?
Yes. Fairfield County reported about 930 of its 2,784 tests at or above 4 pCi/L. That is about what Connecticut as a whole reports (35.1%), and ranks Fairfield County 6th of the 8 Connecticut counties with 30 or more tests. Which homes they were, no map can say. How to test a home.
What ground is Danbury built on, as far as radon goes?
53.4% of Danbury sits on what USGS's map calls "Proterozoic massifs", rated moderate for radon potential, radon index 10; another 40.0% is "Carbonate shelf", in the same class. One smaller area makes up the rest.
Is radon higher in the counties around Danbury?
It depends which way you go. 5 of the 7 nearest counties with a figure report a larger share than Fairfield County's 33.4% and 2 a smaller one: from Tolland County (29.4%, 67 miles off) to New London County (48.5%, 71 miles off).
Who tests for or fixes radon in Danbury?
Danbury is the address of 2 businesses in Radon411's directory, 1 listed for testing and 2 for mitigation. Each entry names the public list it came from. Radon professionals in Danbury.
The answers use the published figures of Fairfield County, the county Danbury lies in.
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