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getPermit reads your job details and tells you what a California city expects before you file: which permits the work triggers, the documents and plans you'll need, the fees to budget for, and the common reasons applications in that jurisdiction get bounced back. It produces a clear checklist you can act on. It does not submit to the city for you — you (or your permit person) stay in control of what gets filed.

Is there a human involved, or is it just AI?

Both. The AI does the research and drafts the assessment and checklist; an experienced permit coordinator reviews and approves it before it's treated as authoritative. The human check is the point — it's how we keep it trustworthy in a process where a wrong filing has real consequences.

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Duct replacement permits in California

Last updated September 23, 2026

A plain-English starting point for HVAC contractors. This is general California guidance — fees, forms, and timelines are set by each city.

Short answer

In California, replacing or extending ductwork requires a mechanical permit, and the Energy Code (Title 24, Part 6) treats it as an alteration: replacing a duct system entirely — or adding/replacing more than about 40 linear feet in unconditioned space — generally triggers duct sealing with third-party HERS leakage testing. Ducts must meet the insulation R-value for the climate zone. A C-20 (HVAC) licensed contractor generally pulls it.

The general picture

Ductwork replacement is permitted mechanical work across California, and the review is mostly an Energy Code review. Title 24, Part 6 treats duct work as an alteration: replace the system, or add or replace more than about 40 linear feet in unconditioned space, and duct sealing with third-party HERS leakage verification generally follows — documented on a CF1R-ALT and registered before final. The materials layer is simple but strictly checked: insulation at the climate zone's required R-value (R-6 or R-8 in most cases), joints sealed with mastic or listed UL 181 tape — never cloth-backed duct tape — and flex duct supported so it isn't kinked or compressed. Because the HERS rater is independent, the schedule needs their test and registration between substantial completion and final inspection. Fees, forms, and inspection scheduling are set per city — confirm with the local building department.

Typically needs a permit

The scope above — duct replacement — itself triggers a permit in nearly every California jurisdiction. Specific variations and edge cases are confirmed with the issuing department.

Usually doesn't (general norm)

Maintenance sealing of accessible duct joints (verify locally)
Replacing registers and grilles
Repairing insulation on existing ducts

Documents & plans generally required

Mechanical permit application
Contractor license and city business registration
Duct layout with sizes, materials, and the equipment served
Insulation R-value spec meeting the climate zone (commonly R-6 or R-8)
Energy-compliance form (CF1R-ALT) and HERS registration where testing is triggered
Support/hanger spacing and connection method for flex duct

Common reasons duct replacement applications get bounced

Code-rooted patterns across California — not a city-specific rejection rate.

Missing CF1R-ALT or HERS registration when the scope triggers duct testing
Insulation R-value below the climate-zone requirement
Cloth-backed duct tape as the sealing method — sealing must be mastic or listed (UL 181) tape
Leakage over the allowed percentage at the HERS test
Flex duct unsupported, kinked, or compressed to the point of choking airflow
Scope written as a 'repair' when most of the system is being replaced

The inspection sequence

A typical order — the number of stops and exact sequence vary by jurisdiction and scope.

1Rough inspection where ducts are concealed in framing before cover
2Final inspection with the system complete and the HERS duct-leakage results registered where required

Licensing — who can pull it

Duct replacement in California is generally C-20 (HVAC) licensed work; a B (General Building) contractor may pull within a larger remodel under CSLB rules. The HERS duct test is performed by an independent third-party rater, not the installing contractor.

How this works in your California city

Cities marked have verified local data — portal, fee schedule, and adopted code edition sourced from public city and county documents. Others link to the general HVAC permit guide for that city.

Frequently asked questions

Does a duct repair need a permit?

Small like-for-like repairs are often treated as maintenance, but replacement and extension are permitted mechanical work — and once the altered footage in unconditioned space passes roughly 40 linear feet, the Energy Code's sealing-and-testing requirements generally come with it. Describe the real scope; cities notice 'repairs' that replace half a system.

What leakage does the HERS test allow?

The allowed leakage is a percentage of system airflow set by the Energy Code, and it differs for new, entirely replaced, and altered duct systems. The practical version: mastic at every joint, tested by an independent HERS rater, results registered — an unregistered test doesn't close the permit.

What R-value do ducts need?

Title 24 sets duct insulation by climate zone — commonly R-6 or R-8 for ducts in unconditioned space, with R-8 required in many zones. The CF1R-ALT documents the value for the project's zone, and both the inspector and the HERS rater look at the duct label.

Do I need a separate permit if I'm also replacing the furnace or AC?

Usually one mechanical permit covers both scopes, but the energy paperwork compounds — the equipment changeout triggers its own measures and the duct replacement its own. The trap is pulling an equipment-only permit and 'discovering' the duct replacement at final.

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