Radon levels in Idaho: Moderate
The model predicts a population-weighted basement average of 2.6 pCi/L (model estimate) across Idaho's 44 counties - about 1.4× the US average of 1.8 pCi/L. Above-ground floors average 1.7 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. Measured state test results are shown separately below, labeled with their source and years. How the numbers work.
19 / 44
EPA Zone 1 counties (43%)
20 / 5
Zone 2 / Zone 3 counties
2
counties predicted ≥ 4 pCi/L
37.2%
of measured tests ≥ 4 pCi/L (through 2019 (start year not stated by the source))
Test Idaho - the EPA says "consider fixing" in this range
The predicted basement average here is 2.6 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.
Monitor link goes to the Airthings store - use code RADONGRADE-10OFF at checkout for 10% off any Airthings monitor.
Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.
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What the data says about radon in Idaho
According to the EPA zone map, 19 of Idaho's 44 counties are EPA Zone 1 (43%), 20 are Zone 2 and 5 are Zone 3. Zone 2 (predicted screening average of 2-4 pCi/L) is the most common designation, with the 19 Zone 1 counties marking where the EPA expected the highest potential. Treat the map as a coarse prior: it predates two decades of test data and never replaces a test in your own home.
The 2001-2021 national model predicts a population-weighted basement average of 2.6 pCi/L for Idaho (moderate range, 1.4× the US population-weighted average of 1.8). Of the 44 counties with predictions, 2 are predicted at or above 4 pCi/L, 40 in the 2-4 band and 2 below 2. The highest predicted county is Teton County at 4.4 pCi/L; the lowest is Clearwater County at 1.8 - a 2.6 pCi/L spread that means a statewide average tells you little about any one county.
94.7% of the state's modeled ZIP codes are predicted at or above 2 pCi/L, and 3.3% at or above the 4 pCi/L action level - below the national 4.2% at the action level but above the national 48.7% at 2 pCi/L. With more than half of ZIPs above 2, a test is worth doing before any purchase or renovation here.
Measured data exists for Idaho: Idaho Department of Health and Welfare publishes through 2019 (start year not stated by the source) results for 44 counties (45,517 tests). Weighted by test count, the measured mean is 6.8 pCi/L and 37.2% of results are at or above 4 pCi/L. The county with the largest share of elevated results is Butte County (70.3%); the smallest is Payette County (6.7%). In 41 of the 44 counties with both figures, the measured mean is higher than the model's long-term basement estimate - expected, because state tests are voluntary and skew toward basements and homeowners who suspected a problem. Each county page shows both side by side.
Idaho counties by predicted radon
Sorted highest to lowest predicted basement average (model estimate). 44 counties. The “Measured ≥ 4” column is the share of Idaho Department of Health and Welfare test results at or above 4 pCi/L, through 2019 (start year not stated by the source).
| County | Predicted basement | Upstairs | Grade | EPA zone | Measured ≥ 4 | ZIPs |
|---|---|---|---|---|---|---|
| Teton County | 4.4 pCi/L | 2.9 | High | EPA Zone 2 | 50.3% | 4 |
| Madison County | 4.3 pCi/L | 2.3 | High | EPA Zone 2 | 34.1% | 4 |
| Jefferson County | 4.0 pCi/L | 2.2 | Moderate | EPA Zone 2 | 62.5% | 7 |
| Custer County | 3.7 pCi/L | 2.3 | Moderate | EPA Zone 1 | 60.2% | 5 |
| Kootenai County | 3.7 pCi/L | 2.5 | Moderate | EPA Zone 1 | 54.8% | 11 |
| Blaine County | 3.6 pCi/L | 3.4 | Moderate | EPA Zone 1 | 54.3% | 5 |
| Bear Lake County | 3.4 pCi/L | 2.3 | Moderate | EPA Zone 2 | 64.7% | 6 |
| Lemhi County | 3.2 pCi/L | 2.4 | Moderate | EPA Zone 1 | 54.2% | 7 |
| Camas County | 3.1 pCi/L | 2.1 | Moderate | EPA Zone 1 | 52.3% | 2 |
| Butte County | 3.1 pCi/L | 1.9 | Moderate | EPA Zone 1 | 70.3% | 3 |
| Bingham County | 3.0 pCi/L | 1.8 | Moderate | EPA Zone 2 | 44.3% | 6 |
| Shoshone County | 3.0 pCi/L | 2.0 | Moderate | EPA Zone 1 | 56.5% | 9 |
| Cassia County | 2.9 pCi/L | 1.7 | Moderate | EPA Zone 2 | 52.1% | 5 |
| Fremont County | 2.9 pCi/L | 2.0 | Moderate | EPA Zone 1 | 51.8% | 3 |
| Caribou County | 2.9 pCi/L | 2.2 | Moderate | EPA Zone 2 | 48.6% | 3 |
| Boise County | 2.9 pCi/L | 1.9 | Moderate | EPA Zone 1 | 33.1% | 6 |
| Elmore County | 2.8 pCi/L | 2.3 | Moderate | EPA Zone 1 | 34.4% | 5 |
| Bonneville County | 2.8 pCi/L | 1.7 | Moderate | EPA Zone 2 | 37.1% | 10 |
| Clark County | 2.8 pCi/L | 1.9 | Moderate | EPA Zone 1 | 47.1% | 2 |
| Oneida County | 2.7 pCi/L | 1.8 | Moderate | EPA Zone 2 | 54.8% | 2 |
| Franklin County | 2.7 pCi/L | 2.0 | Moderate | EPA Zone 2 | 44.6% | 6 |
| Bannock County | 2.6 pCi/L | 1.8 | Moderate | EPA Zone 2 | 38.6% | 7 |
| Power County | 2.6 pCi/L | 1.8 | Moderate | EPA Zone 2 | 34.3% | 4 |
| Benewah County | 2.6 pCi/L | 1.8 | Moderate | EPA Zone 1 | 25.8% | 5 |
| Adams County | 2.6 pCi/L | 1.6 | Moderate | EPA Zone 3 | 38.6% | 4 |
| Bonner County | 2.6 pCi/L | 1.7 | Moderate | EPA Zone 1 | 33.3% | 13 |
| Boundary County | 2.5 pCi/L | 2.0 | Moderate | EPA Zone 1 | 25.5% | 3 |
| Lincoln County | 2.5 pCi/L | 1.3 | Moderate | EPA Zone 2 | 35.7% | 3 |
| Jerome County | 2.4 pCi/L | 1.4 | Moderate | EPA Zone 2 | 22.7% | 3 |
| Twin Falls County | 2.4 pCi/L | 1.5 | Moderate | EPA Zone 2 | 17.4% | 8 |
| Minidoka County | 2.4 pCi/L | 1.5 | Moderate | EPA Zone 2 | 18.2% | 3 |
| Latah County | 2.4 pCi/L | 1.6 | Moderate | EPA Zone 1 | 26.8% | 9 |
| Gooding County | 2.4 pCi/L | 1.3 | Moderate | EPA Zone 1 | 29.1% | 3 |
| Valley County | 2.4 pCi/L | 1.6 | Moderate | EPA Zone 1 | 24% | 3 |
| Gem County | 2.4 pCi/L | 1.6 | Moderate | EPA Zone 3 | 19.3% | 3 |
| Owyhee County | 2.3 pCi/L | 1.4 | Moderate | EPA Zone 2 | 12.6% | 7 |
| Ada County | 2.3 pCi/L | 1.6 | Moderate | EPA Zone 2 | 22% | 14 |
| Lewis County | 2.3 pCi/L | 1.3 | Moderate | EPA Zone 3 | 31.8% | 2 |
| Payette County | 2.1 pCi/L | 1.3 | Moderate | EPA Zone 2 | 6.7% | 3 |
| Idaho County | 2.1 pCi/L | 1.2 | Moderate | EPA Zone 1 | 32.6% | 12 |
| Washington County | 2.1 pCi/L | 1.2 | Moderate | EPA Zone 3 | 17.9% | 3 |
| Nez Perce County | 2.0 pCi/L | 1.2 | Moderate | EPA Zone 3 | 15.1% | 8 |
| Canyon County | 1.9 pCi/L | 1.3 | Low | EPA Zone 2 | 9.3% | 9 |
| Clearwater County | 1.8 pCi/L | 1.3 | Low | EPA Zone 1 | 31.6% | 5 |
Radon levels in Idaho cities
The 9 most-populous Idaho 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 |
|---|---|---|---|---|---|
| Boise | 235,421 | 2.4 pCi/L | 1.7 | Moderate | 0% |
| Meridian | 134,801 | 2.0 pCi/L | 1.4 | Moderate | 0% |
| Nampa | 114,268 | 1.9 pCi/L | 1.2 | Low | 0% |
| Caldwell | 68,336 | 1.9 pCi/L | 1.2 | Low | 0% |
| Idaho Falls | 68,001 | 2.6 pCi/L | 1.6 | Moderate | 0% |
| Pocatello | 58,064 | 2.5 pCi/L | 1.8 | Moderate | 0% |
| Coeur d'Alene | 56,894 | 2.6 pCi/L | 1.8 | Moderate | 0% |
| Twin Falls | 54,943 | 2.4 pCi/L | 1.5 | Moderate | 0% |
| Post Falls | 44,798 | 4.0 pCi/L | 2.8 | Moderate | 0% |
Highest-radon ZIP codes in Idaho
The 10 Idaho ZIP codes with the highest predicted basement average (model estimate), out of 245 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.
| ZIP | County | Predicted basement | Upstairs | Grade |
|---|---|---|---|---|
| 83422 | Teton County | 5.9 pCi/L | 3.8 | High |
| 83858 | Kootenai County | 5.6 pCi/L | 3.6 | High |
| 83801 | Kootenai County | 4.8 pCi/L | 4.3 | High |
| 83452 | Teton County | 4.5 pCi/L | 2.8 | High |
| 83835 | Kootenai County | 4.4 pCi/L | 3.0 | High |
| 83440 | Madison County | 4.4 pCi/L | 2.3 | High |
| 83442 | Jefferson County | 4.4 pCi/L | 2.3 | High |
| 83333 | Blaine County | 4.1 pCi/L | 3.8 | High |
| 83854 | Kootenai County | 4.0 pCi/L | 2.8 | Moderate |
| 83226 | Custer County | 3.9 pCi/L | 2.2 | Moderate |
Idaho radon questions
- Is radon high in Idaho?
- Idaho's population-weighted predicted basement average is 2.6 pCi/L, about 1.4× the US average of 1.8. 2 of its 44 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 40 are in the 2-4 "consider fixing" range and 2 are below 2. 3.3% of Idaho ZIP codes are predicted at 4 or higher.
- Which Idaho county has the highest radon?
- Teton County has the highest predicted basement average in Idaho at 4.4 pCi/L (EPA Zone 2). The lowest is Clearwater County at 1.8 pCi/L. In measured state test data (through 2019 (start year not stated by the source)), Butte County has the largest share of results at or above 4 pCi/L (70.3%). These are area figures; individual homes in any county can test far higher.
- How many EPA Zone 1 counties are in Idaho?
- 19 of Idaho's 44 counties (43%) are EPA Zone 1 (highest potential), 20 are Zone 2 and 5 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 Idaho?
- Yes - with some urgency. Idaho's predicted average is in the moderate range, and 94.7% of its ZIP codes are predicted at 2 pCi/L or higher. A short-term charcoal kit or a continuous digital monitor will tell you your actual level within days.
- What do actual radon tests show in Idaho?
- Idaho Department of Health and Welfare publishes through 2019 (start year not stated by the source) test results for 44 Idaho counties (45,517 tests). Weighted by test count, the measured mean is 6.8 pCi/L and 37.2% of results are at or above 4 pCi/L. The measured mean is higher than the model's long-term basement estimate in 41 of 44 comparable counties; state tests are voluntary and skew toward basements and homes where radon was suspected, while the model estimates the average across all homes.
Idaho radon program
Idaho's radon program page is at healthandwelfare.idaho.gov and, when we checked it, offered a free test kit (one per address every two years; listed as out of stock when checked). 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.