Locations and reports
Radon in Boise, Idaho
EPA puts Ada County, where Boise is, in Zone 2, its middle radon zone, and 25.2% of its 3,030 reported radon tests (2008 to 2017, laboratory totals) 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
25.2%
16.3 pts below ID
- Ada
- 25.2%
- Idaho
- 41.5%
Ada, 26th of 37 in ID, 2008 to 2017
Median result
2.4pCi/L
Below action level
- Ada
- 2.4 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of Ada's tests, 2008 to 2017
Nearest county
10.7%
Canyon, 24 miles
- Canyon
- 10.7%
- Ada
- 25.2%
563 tests, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
Ada, where Boise is
Tests reported
3,030
In Ada
- Ada
- 3,030
- Canyon
- 563
Reported to CDC before any fix, 2008 to 2017
Read a result for Boise
Starts at Ada County's median, 2.4 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.4 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. Ada County's median reported result, 2008 to 2017.
The data
Boise, What is published
What is published for Boise
Every figure for Boise is a county's
Radon data is published by county, not by city, so for Boise it is Ada County's: its EPA zone (Zone 2) and the 3,030 tests reported to CDC for 2008 to 2017, laboratory. Only a test tells you about one home.
Boise covers 84 square miles of land, all of it in Ada County. About 238,429 people live there, 2,837 to the square mile.
Boise, Counties
The county Boise lies in
MeasuredAda County's EPA zone and the figures CDC publishes for it, 2008 to 2017, laboratory.
Ada CountyZone 2Moderate predicted potential
- 25.2%
- Reported tests at or above 4 pCi/L
- 2.4 pCi/L
- Median reported result
- 3,030 tests
- Tests reported to CDC
- None
- Yearly figures on file
Ada County ranks 26th of 37 Idaho counties with 30 or more tests for that period, 16.3 points below the 41.5% pooled across Idaho's counties, 10.5 points below the national pool of 35.7%.
Measured from the middle of Boise, the nearest counties with a CDC figure for 2008 to 2017, laboratory are Canyon County (24 miles, 10.7% of 563 tests), Gem County (33 miles, 20.2% of 99 tests) and Boise County (37 miles, 22.4% of 58 tests). Across the 8 nearest, the share at or above 4 pCi/L runs from 4.9% to 48.1%; the farthest of them, Gooding County, is 84 miles away at 28.4%.
No business in the directory gives Boise as its address; the Idaho list covers it. Idaho's other cities with a page of their own: Coeur d'Alene.
The counties around Boise
By distance from the middle of Boise; counties with 30 or more tests.
Predicted: EPA Map of Radon Zones, by county. Measured: CDC tracking data, by county, 2008 to 2017, laboratory.
Boise, Geology
The ground under Boise
PredictedMost of the ground under Boise is one class on USGS's geologic map: 96.4% of its land is moderate radon potential, with 3.6% high. 96.4% of it lies in the area the map calls Eastern Snake river plain and Malheur-Boise-King Section, to which USGS gives a radon index of 10, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Eastern Snake river plain and Malheur-Boise-King Section | Basalt flows. | Moderate | 10 | 96.4% |
| Northern Rocky Mountain Province | Diorite and granite of the Idaho batholith. | High | 12 | 3.6% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Boise beside its county and Idaho
The ground under Boise is close to Ada County's as a whole: 3.6% rated high against 11.4%. Idaho as a whole has more high-potential ground than Boise: 50.7% of its land, against 3.6% here.
The map rates the ground, not the air in any home.
Boise, Homes
Homes in Boise
Of Boise's 104,833 homes, 65% are detached houses, against 75% across Ada County; 17% are in buildings of five or more homes. The homes are older than Ada County's as a whole: half were built before 1985 (1996 for Ada County), and 17% date from before 1960. 63% of occupied homes are lived in by their owner (Ada County: 71%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Boise | Ada County | Idaho |
|---|---|---|---|
| Housing units | 104,833 | 205,068 | 776,683 |
| Detached houses | 65% | 75% | 74% |
| In buildings of 5 or more | 17% | 11% | 9% |
| Mobile homes | 3% | 3% | 7% |
| Built before 1960 | 17% | 10% | 18% |
| Built since 2000 | 23% | 43% | 35% |
| Middle year built | 1985 | 1996 | 1990 |
| Owner-occupied | 63% | 71% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.
Local help
Boise, Local resources
Local resources for Boise
Who to ask in Idaho: its radon program, test kits and professionals.
- DHW Environmental Health ProgramRun by Idaho Department of Health and Welfare, phone 800-445-8647.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Order a free radon test kit.
- Compare kits
- Professionals in IdahoRadon testers and mitigators in Idaho, each with how its listing was checked.
The program's own words on licensing are on the Idaho page.
What it means
Boise, Questions
Questions about radon in Boise
What radon zone is Boise in?
Boise has no zone of its own: it shares Ada County's, Zone 2, the map's middle class: a predicted county average of 2 to 4 pCi/L.
What are radon levels in Boise?
Around Boise, 25.2% of 3,030 tests reported from Ada County for 2008 to 2017 (laboratory totals) reached 4 pCi/L or more, so a high result is no surprise here. The median reported result was 2.4 pCi/L.
Should I test my home in Boise?
Yes. Ada County reported about 764 of its 3,030 tests at or above 4 pCi/L. That is below Idaho's pooled 41.5%, and still not a reason to skip it, and ranks Ada County 26th of the 37 Idaho counties with 30 or more tests. Which homes they were, no map can say. How to test a home.
What ground is Boise built on, as far as radon goes?
USGS's geologic map puts all of Boise on one named area, "Eastern Snake river plain and Malheur-Boise-King Section", rated moderate for radon potential, radon index 10.
Is radon higher in the counties around Boise?
It depends which way you go. 2 of the 8 nearest counties with a figure report a larger share than Ada County's 25.2% and 6 a smaller one: from Payette County (4.9%, 39 miles off) to Elmore County (48.1%, 42 miles off).
The answers use the published figures of Ada County, the county Boise lies in.
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