How a radon system works
CDPH calls active sub-slab suction, also called sub-slab depressurization, the most common and usually the most reliable radon reduction method. It says mitigation can bring most homes to 2 pCi/L or less.
What radon mitigation costs in California: estimates, not quotes
Our estimate for a mitigation system is $1,275 to $2,875 per system, installed. It's a model and not a quote, built from one national published range widened by 15 percent each side and adjusted by California's construction laborer wage ratio, with no California company price behind it.
Estimated range, not a quote: $1,275 to $2,875 per system, installed. Built from one national published range, adjusted by the California construction laborer wage ratio (1.25). Two California foundation companies publish prices (Quartz Construction in San Jose, a range table; Avalon Structural near San Jose, inspection fees); that is too few to anchor a California range, so no company price moves the estimate. Basis: no state company sample (no counted California company price for this job), national estimate only.
Estimated range. Built from national published ranges (1 source), adjusted by California's construction laborer wage ratio to the US (1.25, BLS May 2025). Not a quote. Only two of the 18 California foundation companies we looked at publish a price we could count, so no company price anchors the estimates. We have no counted California company price for this job, so the range is our national estimate alone. Full method. Prices as of Oct 23, 2026.
Who should run the test
CDPH's testing page says to fix a home at 4 pCi/L or more. The company that tests often sells the fix, so use a kit or a tester you hire only to test, and keep the result before you collect estimates.
The California Geological Survey publishes an interactive radon potential map and Special Report 247, California Indoor Radon Potential (2022), for finer detail than the county zones.
EPA radon zones by California county
EPA puts two California counties, Santa Barbara and Ventura, in Zone 1, where the predicted average indoor level is above 4 pCi/L. Twenty-nine counties are Zone 2, 2 to 4 pCi/L, including Alameda, Los Angeles, Monterey, San Luis Obispo and Santa Clara. Twenty-seven are Zone 3, below 2 pCi/L, including Fresno, Imperial, Marin, Orange, Sacramento, San Diego, San Joaquin, Sonoma and Yolo. A county zone describes an average, not your house.
Who may provide radon services in California
H&SC 106780 says no person may provide radon services for the general public, or represent or advertise them, unless certified under the National Radon Proficiency Program or the National Radon Safety Board, and CDPH lists the certified providers. Ask for the certificate number and check it against that list.
Radon situations that are emergencies
- If gas is in the air anywhere in the house, get outside, then call 911 and the gas utility.
- Water is rising around a radon fan or its wiring: stay out of it and call for help.
- A test at or above 4 pCi/L, which CDPH says to fix; compare certified providers' estimates first.
- A result below 4 pCi/L, which is under CDPH's fix level.
Steps before you hire a radon company
- Get a short-term test kit, or hire a certified tester, and follow the kit's instructions on placement.
- Keep the written result, with its date, to show each company.
- Ask each company for its NRPP or NRSB certificate number and what happens if the number stays high after the fan is in.
Permit and certification position for radon work
Ask your building department whether a mitigation system needs a permit, since the sources we have don't address it. The certification rule applies to anyone offering radon services to the public.
Ask for the contractor's license number and check it with your state licensing agency before you sign anything.
Questions people ask
Does California require radon contractors to be certified?
H&SC 106780 says no person may provide radon services for the general public, or represent or advertise them, unless certified under the National Radon Proficiency Program or the National Radon Safety Board. CDPH lists certified providers.
At what level should radon be fixed?
CDPH's testing page sets the fix level at 4 pCi/L or more, and says mitigation can bring most homes to 2 pCi/L or less.
Is California a high-radon state?
EPA lists 2 Zone 1 counties, 29 Zone 2 counties and 27 Zone 3 counties in California. A county's zone is a prediction of the average, so test the house you live in.
How much does radon mitigation cost in California?
Our estimate is $1,275 to $2,875 per system, installed, built from one national range and adjusted for California wages. Ask each company for a written scope that includes the post-installation test.
What is the most common radon fix?
CDPH describes active sub-slab suction, also called sub-slab depressurization, as the most common and usually the most reliable method. Its pages don't describe crawl space variants.
- CDPH: Radon and Real Estate; Radon Fix; Radon Testing Read Oct 20, 2026.
- CDPH: Indoor Radon Program (and Radon Regulations and Standards page) Read Oct 20, 2026.
- EPA Map of Radon Zones spreadsheet (county table), with EPA California map PDF Read Oct 20, 2026.
- U.S. Bureau of Labor Statistics, OEWS May 2025: Construction Laborers (SOC 47-2061), California, mean hourly wage Read Oct 23, 2026.
- U.S. Bureau of Labor Statistics, OEWS May 2025: Construction Laborers (SOC 47-2061), United States, mean hourly wage Read Oct 23, 2026.
- FoundationMatch: how we estimate costs, California (editorial policy) Read Oct 23, 2026.