San Mateo County HVAC Permits

County vs. City: The Jurisdiction Question

This is the single most important thing to understand before you file a permit in San Mateo County: the County of San Mateo Planning and Building Department only handles permits for unincorporated areas. If the property is within the city limits of San Mateo, Redwood City, Foster City, or any other incorporated city, you file with that city's building department, not the county. This trips up contractors constantly. You get a job in "Redwood City" and assume you're filing with the City of Redwood City, but the address is actually in unincorporated Redwood City, which means the county has jurisdiction. Or vice versa. Always verify the jurisdiction before you start your application, because filing with the wrong agency wastes everyone's time and you'll have to start over.

The unincorporated areas of San Mateo County are scattered throughout the peninsula. Some of the more common ones where you'll be doing HVAC work include Emerald Hills, Devonshire, Palomar Park, parts of the hills west of Redwood City, areas near Woodside, and pockets throughout the county that never incorporated into neighboring cities. The county's website has a jurisdiction lookup tool, and you should use it for any address you're not 100% sure about. You can also call the county planning department and they'll tell you on the spot whether an address falls under their jurisdiction.

Where to File Your County HVAC Permit

The San Mateo County Planning and Building Department is located at 455 County Center in Redwood City. They offer online permit submission through their electronic portal, and for standard residential HVAC work, the online process works well. The county's system is functional if not flashy. You'll create an account, fill out the application, upload your documents, and pay fees electronically. For contractors who are used to filing with cities like San Mateo or Redwood City, the county process feels slightly different. The forms are county forms, not city forms, and the fee structure and review process have their own quirks.

The counter staff at the county building department are generally helpful, though the department serves a large geographic area and handles everything from rural properties in the coastal hills to suburban homes in Emerald Hills. The range of projects they review is broad, which means the staff see a lot of variety. If you have questions about a specific property or project, don't hesitate to call ahead. The county planners can help you understand any special conditions that might apply to the property, such as hillside development requirements or fire zone restrictions, which are more common in unincorporated areas than in cities.

What Permits You Need

The county follows the same California permit framework as the cities. HVAC installations and replacements require a mechanical permit. Gas line work needs a plumbing permit. Electrical modifications need an electrical permit. The county allows combined trade permit applications for residential projects. The documentation requirements are comparable to what the incorporated cities expect: equipment specifications, load calculations, energy compliance documents, and a site plan showing equipment locations.

One difference you'll notice with county permits is that unincorporated properties sometimes have conditions attached to them that city properties don't. Properties in fire hazard zones, which are common in the hillside areas of unincorporated San Mateo County, may have additional requirements for equipment placement and clearances. Properties with septic systems rather than city sewer connections may have setback requirements that affect where you can place outdoor equipment. And properties in designated rural areas may have different access requirements that affect how the inspector gets to the site. These aren't things you typically worry about on a suburban HVAC job in a city, but they come up regularly in unincorporated county areas.

Fees and What to Budget

San Mateo County HVAC permit fees are reasonable, generally ranging from $100 to $350for residential work. A straightforward equipment replacement with no gas or electrical modifications will typically run $100 to $175. Full system installs with multiple trade permits and plan review push toward the $250 to $350 range. The county publishes their fee schedule, and the online system provides an estimate during the application process. There are some standard county surcharges for technology, records management, and building standards administration, but they're in line with what the surrounding cities charge.

If the property is in a hillside development area or a fire hazard zone, there may be additional review fees beyond the standard building permit fees. These aren't common for routine HVAC work, but if your project triggers additional review requirements, the fees can add up. Ask the county staff about any special conditions on the property before you finalize your bid, so you can account for any additional permitting costs.

Realistic Timelines

Expect 1 to 2 weeksfor standard residential HVAC permit processing through the county. Simple changeouts that don't require plan review can sometimes be approved faster, but the county's processing times tend to run slightly longer than the incorporated cities, simply because the department covers such a large geographic area with a modest staff. During busy periods, especially spring and summer when construction activity peaks, processing times can stretch toward the two-week mark or beyond for more complex projects.

Inspection scheduling is where the county process can differ most from city permits. Because the unincorporated areas are spread across a wide geography, from coastal properties south of Half Moon Bay to hillside homes above Redwood City, the inspectors cover a lot of ground. Inspection wait times can be longer than in a compact city, sometimes three to five business days rather than the one to two days that's common in cities. For properties in remote or hard-to-access locations, you may need to coordinate with the inspector about site access, gate codes, or road conditions. Plan your project schedule with these longer inspection windows in mind.

Title 24 and HERS Testing Requirements

Title 24 energy compliance applies to all HVAC work in unincorporated San Mateo County, just as it does in every California jurisdiction. You'll submit CF-1R compliance documents with your permit application. The county plan reviewers check these documents, so make sure your equipment model numbers, efficiency ratings, and building envelope characteristics are accurate and consistent across all your submittals. The unincorporated areas include a range of climate conditions, from foggy coastal areas to warmer inland valleys, and your energy calculations need to reflect the actual climate zone for the specific property.

HERS testing is required after installation. A certified HERS rater will verify duct leakage, refrigerant charge, and system airflow. For properties in the hillside areas, be aware that some homes have unusual construction characteristics, older ductwork in unconventional routing, or building envelopes that don't match standard assumptions. These can affect your HERS test results, so assess the existing conditions carefully before the install and plan your duct sealing and system setup accordingly. Schedule your HERS rater before requesting the county final inspection, as the inspector will expect to see the verification certificate.

Common Gotchas in the County

Beyond the jurisdiction confusion, the biggest gotcha in unincorporated San Mateo County is property access and site conditions. Many of the hillside properties in Emerald Hills, Devonshire, and the areas above Woodside have steep driveways, narrow roads, and limited staging areas. Getting equipment to the installation location can be a project in itself. Factor this into your bid and timeline, because a condenser that takes 20 minutes to place at a suburban tract home might take half a day to position at a hillside property with a 300-foot driveway and no crane access.

Properties in fire hazard severity zones, which include much of the unincorporated hillside area, have specific vegetation clearance and defensible space requirements. While these are primarily the homeowner's responsibility, they can affect equipment placement. Outdoor condensers need adequate clearance from vegetation and structures, and in fire zones, the inspector may be stricter about these clearances than you'd experience in a city. Some properties also have easements, drainage conditions, or other recorded restrictions that affect where you can place equipment. Check the property records or ask the homeowner about any known restrictions before you finalize your plans.

Learn More

For a comprehensive overview of HVAC permitting, check out our HVAC Permit Guide. If you also work within the incorporated cities nearby, our Redwood City permit guide and San Mateo permit guide cover those jurisdictions. And for a look at how AI is streamlining the permit process, see our article on AI-powered permit filing.