San Francisco County, CA radon potential

EPA's own radon map rates San Francisco County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. San Francisco County sits at the 65th percentile nationally for radon potential — above 65 of every 100 rated counties.

San Francisco County by the numbers

San Francisco County, California is home to about 827,526 people across 46.685 square miles. Population density there runs about 17,726 people per square mile. Within its own EPA zone, San Francisco County is bigger by population than 98% of the counties that share it. EPA's geology-based Region 9 groups San Francisco County with 94 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

San Francisco County's predicted average falls between EPA's 4 pCi/L action level and the national indoor average of about 1.3 pCi/L (outdoor air runs roughly 0.4 pCi/L). Middle-of-the-pack doesn't mean risk-free for any one San Francisco County address — a moderate county average still leaves individual homes to test either side of it.

Next steps for a home in San Francisco County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find California's state radon program

For San Francisco County, an ongoing number beats a one-time test - a Airthings radon monitor tracks San Francisco County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where San Francisco County's figures come from

San Francisco County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone San Francisco County carries, the zone explainer covers what it does and doesn't tell you about any one house.