Radon levels in Connecticut: Low
The model predicts a population-weighted basement average of 1.5 pCi/L (model estimate) across Connecticut's 8 counties - about 16% below the US average of 1.8 pCi/L. Above-ground floors average 1.0 pCi/L.
Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.
4 / 8
EPA Zone 1 counties (50%)
3 / 1
Zone 2 / Zone 3 counties
0
counties predicted ≥ 4 pCi/L
0%
of ZIP codes predicted ≥ 4 pCi/L
Test Connecticut once anyway - radon varies house to house
The predicted basement average here is 1.5 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.
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What the data says about radon in Connecticut
On the EPA's 1993 radon zone map, 4 of Connecticut's 8 counties are EPA Zone 1 (50%), 3 are Zone 2 and 1 is Zone 3. Zone 1 - the highest-potential class, predicted screening average above 4 pCi/L - is the most common designation in Connecticut. That classification has not been revised since 1993; it describes counties, not homes, and elevated readings turn up in Zone 3 counties every year.
Connecticut models out at 1.5 pCi/L predicted basement average (low; 16% below the US average of 1.8). Of the 8 counties with predictions, 0 are predicted at or above 4 pCi/L, 0 in the 2-4 band and 8 below 2. The county range is narrow: from Hartford County at 1.25 to Windham County at 1.99 pCi/L, a spread of only 0.74.
At ZIP-code resolution, 0% of Connecticut ZIPs are predicted at 4 pCi/L or higher in the basement and 26% at 2 or higher - below the national shares of 4.2% and 48.7%. No ZIP in the state is predicted above 4 on average - but averages hide individual homes, which is why the EPA still asks everyone to test.
Connecticut counties by predicted radon
Sorted highest to lowest predicted basement average (model estimate). 8 counties.
| County | Predicted basement | Upstairs | Grade | EPA zone | ZIPs |
|---|---|---|---|---|---|
| Windham County | 2.0 pCi/L | 1.3 | Low | EPA Zone 2 | 23 |
| New London County | 1.8 pCi/L | 1.3 | Low | EPA Zone 1 | 27 |
| Tolland County | 1.8 pCi/L | 1.2 | Low | EPA Zone 2 | 15 |
| Litchfield County | 1.8 pCi/L | 1.2 | Low | EPA Zone 2 | 37 |
| Middlesex County | 1.6 pCi/L | 1.1 | Low | EPA Zone 1 | 20 |
| Fairfield County | 1.6 pCi/L | 1.2 | Low | EPA Zone 1 | 46 |
| New Haven County | 1.5 pCi/L | 1.0 | Low | EPA Zone 1 | 40 |
| Hartford County | 1.3 pCi/L | 0.7 | Low | EPA Zone 3 | 54 |
Radon levels in Connecticut cities
The 15 most-populous Connecticut places among the 1,000 largest US cities (Census incorporated places and CDPs), by population. City figures are ZIP-land-weighted means of the model's ZIP predictions (model estimate).
| City | Population | Predicted basement | Upstairs | Grade | ZIPs ≥ 4 |
|---|---|---|---|---|---|
| Bridgeport | 148,028 | 1.4 pCi/L | 0.8 | Low | 0% |
| Stamford | 136,226 | 1.6 pCi/L | 1.4 | Low | 0% |
| New Haven | 135,319 | 1.2 pCi/L | 0.6 | Low | 0% |
| Hartford | 119,669 | 1.0 pCi/L | 0.5 | Low | 0% |
| Waterbury | 114,990 | 1.6 pCi/L | 0.9 | Low | 0% |
| Norwalk | 92,458 | 1.6 pCi/L | 1.2 | Low | 0% |
| Danbury | 86,124 | 1.4 pCi/L | 1.0 | Low | 0% |
| New Britain | 74,080 | 1.2 pCi/L | 0.6 | Low | 0% |
| West Hartford | 63,268 | 1.2 pCi/L | 0.7 | Low | 0% |
| Bristol | 61,601 | 1.3 pCi/L | 0.8 | Low | 0% |
| Meriden | 60,111 | 1.3 pCi/L | 0.7 | Low | 0% |
| West Haven | 54,790 | 1.1 pCi/L | 0.9 | Low | 0% |
| East Hartford | 51,252 | 1.0 pCi/L | 0.6 | Low | 0% |
| Milford | 50,421 | 1.8 pCi/L | 1.3 | Low | 0% |
| Middletown | 47,984 | 1.1 pCi/L | 0.7 | Low | 0% |
Highest-radon ZIP codes in Connecticut
The 10 Connecticut ZIP codes with the highest predicted basement average (model estimate), out of 262 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.
| ZIP | County | Predicted basement | Upstairs | Grade |
|---|---|---|---|---|
| 06419 | Middlesex County | 2.9 pCi/L | 1.5 | Moderate |
| 06441 | Middlesex County | 2.5 pCi/L | 1.6 | Moderate |
| 06384 | New London County | 2.4 pCi/L | 1.7 | Moderate |
| 06027 | Hartford County | 2.4 pCi/L | 1.6 | Moderate |
| 06259 | Windham County | 2.4 pCi/L | 1.4 | Moderate |
| 06482 | Fairfield County | 2.3 pCi/L | 1.6 | Moderate |
| 06250 | Tolland County | 2.3 pCi/L | 1.6 | Moderate |
| 06370 | New London County | 2.3 pCi/L | 1.6 | Moderate |
| 06420 | New London County | 2.3 pCi/L | 1.7 | Moderate |
| 06751 | Litchfield County | 2.3 pCi/L | 1.6 | Moderate |
Connecticut radon questions
- Is radon high in Connecticut?
- Connecticut's population-weighted predicted basement average is 1.5 pCi/L, about 16% below the US average of 1.8. 0 of its 8 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 0 are in the 2-4 "consider fixing" range and 8 are below 2. 0% of Connecticut ZIP codes are predicted at 4 or higher.
- Which Connecticut county has the highest radon?
- Windham County has the highest predicted basement average in Connecticut at 2.0 pCi/L (EPA Zone 2). The lowest is Hartford County at 1.3 pCi/L. These are area figures; individual homes in any county can test far higher.
- How many EPA Zone 1 counties are in Connecticut?
- 4 of Connecticut's 8 counties (50%) are EPA Zone 1 (highest potential), 3 are Zone 2 and 1 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.
- Should I test for radon in Connecticut?
- Yes. Even though Connecticut's predicted average is below 2 pCi/L, the EPA recommends every home be tested - radon varies house to house, and 26% of Connecticut ZIP codes are still predicted at 2 pCi/L or higher.
Connecticut radon program
Connecticut's radon program page is at portal.ct.gov; it lists testing and certified-mitigator guidance for the state. The EPA also keeps a directory of every state radon contact: EPA state radon contacts page. Then read how to test and what mitigation costs.