Is radon high in San Mateo, California?

Low. Averaging the model's ZIP-code predictions across San Mateo (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.4 pCi/L - about 23% below the US average of 1.8 and close to the California average of 1.5. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. San Mateo ranks 157 of 207 California cities on this site.

Which San Mateo ZIP codes have the highest radon?

Predictions for the 4 modeled ZIP codes in San Mateo range from 1.3 to 1.5 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 San Mateo?

Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; San Mateo's low predicted average describes the typical home, not yours.

What does EPA Radon Zone 2 mean for San Mateo?

San Mateo sits mainly in San Mateo 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 1.4 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.

Radon levels in San Mateo, California

LowEPA Zone 2

Predicted long-term basement average of 1.4 pCi/L (model estimate) across the 4 modeled ZIP codes in San Mateo - about 23% below the US average of 1.8, close to the California average of 1.5. Ranked #157 of 207 California cities on this site. Most of the city lies in San Mateo County.

Test San Mateo, CA once anyway - radon varies house to house

The predicted basement average here is 1.4 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.

Get a short-term test kit →Or track it with a continuous monitor

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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. How the numbers work.

1.4 ± 0.06

pCi/L predicted basement mean (model SD)

0.6 ± 0.08

pCi/L predicted upstairs (above-ground) mean

1.3-1.5

range of ZIP-level basement predictions in the city

of San Mateo ZIPs predicted ≥ 4 pCi/L (0% ≥ 2)

What this means for San Mateo

The typical San Mateo home is predicted below 2 pCi/L, the lowest band. That describes the average house; the ZIP-level predictions inside the city still span 1.3 to 1.5 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 San Mateo County as Zone 2 while the newer model predicts 1.4 pCi/L for San Mateo; where they disagree, we grade on the model but show both.

Comparable California cities: Vacaville (1.4), Norwalk (1.4), Lodi (1.4), Cypress (1.4).

ZIP codes in San Mateo

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
94403	45%	1.3 ± 0.06	0.6	Low
94401	26%	1.4 ± 0.06	0.6	Low
94402	25%	1.5 ± 0.06	0.6	Low
94404	5%	1.4 ± 0.06	0.7	Low

Testing help in California

California's radon program page is at www.cdph.ca.gov; it lists testing and certified-mitigator guidance. 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.

San Mateo radon questions

Is radon high in San Mateo, California?: Low. Averaging the model's ZIP-code predictions across San Mateo (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.4 pCi/L - about 23% below the US average of 1.8 and close to the California average of 1.5. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. San Mateo ranks 157 of 207 California cities on this site.
Which San Mateo ZIP codes have the highest radon?: Predictions for the 4 modeled ZIP codes in San Mateo range from 1.3 to 1.5 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 San Mateo?: Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; San Mateo's low predicted average describes the typical home, not yours.
What does EPA Radon Zone 2 mean for San Mateo?: San Mateo sits mainly in San Mateo 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 1.4 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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