Radon levels in Nampa, Idaho
LowEPA Zone 2Predicted long-term basement average of 1.9 pCi/L (model estimate) across the 3 modeled ZIP codes in Nampa - close to the US average of 1.8, about 26% below the Idaho average of 2.6. Ranked #8 of 9 Idaho cities on this site. Most of the city lies in Canyon County.
Test Nampa, ID once anyway - radon varies house to house
The predicted basement average here is 1.9 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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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.
1.9 ± 0.05
pCi/L predicted basement mean (model SD)
1.2 ± 0.06
pCi/L predicted upstairs (above-ground) mean
1.9-2.0
range of ZIP-level basement predictions in the city
0%
of Nampa ZIPs predicted ≥ 4 pCi/L (0% ≥ 2)
Measured radon tests in Canyon County (Idaho Department of Health and Welfare, through 2019)
Actual results from home radon tests reported to the state, separate from the model estimate above. Coverage: through 2019 (start year not stated by the source).
- Measured mean
- 2.0 pCi/L
- Results ≥ 4 pCi/L
- 9.3%
- Sample
- 1,803 tests
| Figure | Model (predicted) | State tests (measured) |
|---|---|---|
| Mean, pCi/L | 1.9 basement | 2.0 |
| Share ≥ 4 pCi/L | not a model output | 9.3% |
The model and the state test data land within a few tenths of a pCi/L of each other here; the model estimates a long-term basement average while the tests are voluntary, mostly short-term results.
Source: Home Radon Test Results by Zip Code, Idaho Department of Health and Welfare, Indoor Environment / Radon Program. No license statement on the public feature service (publicly shared by the IDHW environmental-health account). Method and download.
What this means for Nampa
The typical Nampa home is predicted below 2 pCi/L, the lowest band. That describes the average house; the ZIP-level predictions inside the city still span 1.9 to 2.0 pCi/L.
The city figure is not a separate estimate: it is the mean of the model's ZIP-code predictions, weighted by the share of the city's land in each ZIP (Census 2020 ZCTA-to-place relationship file). Note that the EPA classifies Canyon County as Zone 2 while the newer model predicts 1.9 pCi/L for Nampa; where they disagree, we grade on the model but show both.
Comparable Idaho cities: Meridian (2.0), Caldwell (1.9), Boise (2.4), Twin Falls (2.4).
ZIP codes in Nampa
ZIPs that overlap the city, largest share of its land first. Predicted basement and upstairs means are model estimates; ZIPs the model does not cover show a dash.
| ZIP | Share of city | Basement | Upstairs | Grade |
|---|---|---|---|---|
| 83687 | 47% | 2.0 ± 0.05 | 1.2 | Low |
| 83686 | 31% | 2.0 ± 0.06 | 1.2 | Low |
| 83651 | 23% | 1.9 ± 0.05 | 1.3 | Low |
Testing help in Idaho
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). EPA state radon contacts page. If a test comes back at 4 pCi/L or higher, mitigation typically costs $800-$2,500 installed; use EPA find-a-professional and read the mitigation guide.
Nampa radon questions
- Is radon high in Nampa, Idaho?
- Low. Averaging the model's ZIP-code predictions across Nampa (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.9 pCi/L - close to the US average of 1.8 and about 26% below the Idaho average of 2.6. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Nampa ranks 8 of 9 Idaho cities on this site.
- What do actual radon tests show around Nampa?
- Idaho Department of Health and Welfare publishes results for Canyon County (not the city alone) covering through 2019 (1,803 tests): an average of 2.0 pCi/L, 9.3% of results at or above the 4 pCi/L action level. These are voluntary home tests, so they skew toward basements and toward homes where radon was suspected; the model's predicted basement average for Nampa is 1.9 pCi/L.
- Which Nampa ZIP codes have the highest radon?
- Predictions for the 3 modeled ZIP codes in Nampa range from 1.9 to 2.0 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 0% at or above 2. The city is fairly uniform, so the city-wide number is a reasonable guide for any neighborhood.
- Should I test for radon in Nampa?
- Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; Nampa's low predicted average describes the typical home, not yours.
- What does EPA Radon Zone 2 mean for Nampa?
- Nampa sits mainly in Canyon County, which the EPA classifies as Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 1.9 pCi/L does not line up with Zone 2, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.
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