- Replacing a commercial HVAC system is usually an 'alteration' under California's energy code (Title 24, Part 6), so the new equipment must meet current requirements, not the old design.
- Permits are issued by the local building department (the AHJ), and requirements vary by city. Mechanical, electrical, and sometimes gas and structural items are reviewed.
- Acceptance testing and certificates of installation are how the code verifies the system was installed to spec. They are part of the project, not an optional extra.
- Seismic anchorage, roof structural capacity, and crane logistics are commonly overlooked and can delay projects.
- Gas equipment in Orange County must also meet South Coast AQMD requirements.
Why replacement isn't just like-for-like
Owners often assume a new rooftop unit can simply replace the old one. In California, replacing mechanical equipment in an existing nonresidential building typically triggers current energy-code requirements for the altered system. The code that applies is the edition in effect when the permit is applied for; the 2025 edition of Title 24 took effect January 1, 2026.
That can affect the efficiency of the unit you select, whether an economizer is required, the controls and fault detection included, duct sealing or testing if ductwork is altered, and the documentation that must be completed.
Common triggers and requirements
| Scope of work | Often triggers |
|---|---|
| Replace a packaged RTU | Minimum efficiency compliance, economizer requirements (size and climate-zone dependent), thermostat and control requirements, fault detection and diagnostics, acceptance testing |
| Replace split system or condensing unit | Efficiency and refrigerant requirements, line-set and duct considerations, acceptance tests where applicable |
| Alter or replace ductwork | Duct sealing and leakage testing, insulation requirements |
| Add or change controls | Control sequences, setpoint and scheduling requirements, demand-control ventilation in applicable spaces |
| Replace gas water heater or boiler | Combustion air and venting, SCAQMD NOx rules, efficiency, pipe insulation |
| New or replaced walk-in refrigeration | Appliance efficiency standards (Title 20 and federal), components such as ECM motors and LED lighting |
Climate zone matters. Most of Orange County falls in California Title 24 climate zones 6 or 8, though pockets differ. Your contractor can confirm by ZIP code through the California Energy Commission lookup.
How permits work
- Scope and documents. Equipment submittals, manufacturer data, and energy compliance forms are prepared.
- Permit application to the local building department (the AHJ). Orange County has dozens of jurisdictions with their own portals, fees, and review times.
- Plan check where required. Like-for-like replacements are sometimes processed over the counter or online; larger or structural changes need full review.
- Installation after permit issuance.
- Inspections: rough and final, plus any required acceptance testing.
- Final sign-off and close-out documents delivered to the owner.
Skipping permits exposes owners to stop-work orders, failed inspections at sale or refinance, insurance issues, and fines. A contractor who suggests no permit is needed for a rooftop replacement is a red flag.
Acceptance testing and compliance forms
Nonresidential energy compliance uses a set of certificates: a Certificate of Compliance (design intent), a Certificate of Installation (what was installed), and Certificates of Acceptance (functional test results). For mechanical systems, required acceptance tests can include economizer operation, fault detection and diagnostics, supply-fan controls, and ventilation controls. Many of these tests must be performed by a certified acceptance test technician and submitted to the building department.
Ask your contractor who performs acceptance testing, when it will be scheduled, and who files the paperwork. Delays in acceptance testing are a leading reason final inspection slips.
Roof, seismic, and logistics
- Roof structure: A new unit can weigh more or have a different footprint than the old one. Verify roof capacity and curb compatibility.
- Seismic anchorage: California requires equipment on roofs to be anchored and braced for seismic forces. Details depend on weight, height, and building type.
- Curb adapters: Frequently needed when new unit dimensions differ; they must be flashed and sealed to protect roofing warranties.
- Crane and street access: Large units need crane time and often a street-use or encroachment permit. Coordinate with property management, neighbors, and parking.
- Roofing warranty: Penetrations and curb changes can affect roof warranties; notify the roofer of record when required.
- Screening and appearance: Some cities, HOAs, and landlords regulate rooftop equipment screening and height.
Electrical, gas, and emissions
- Verify electrical service capacity, disconnects, and wire sizing for the new unit; heat pump or high-efficiency units may have different loads.
- Gas piping capacity and venting must match the new equipment.
- In the South Coast AQMD, gas-fired water heaters and small boilers are regulated for NOx; see commercial water heaters and boilers.
- Utility rebates and incentive programs may be available. Apply before purchase when required.
A realistic replacement timeline
| Phase | Typical range | What drives it |
|---|---|---|
| Survey and selection | Days to 2 weeks | Access, site conditions, owner decisions |
| Equipment lead time | Days to many weeks | Unit size, manufacturer stock, special options |
| Permit | Same-day to several weeks | Jurisdiction, scope, plan check |
| Installation | 1–3 days per unit (crane day plus finish work) | Crane access, curb condition, electrical and gas work |
| Inspection and acceptance testing | Days to 2 weeks | Inspector availability, tester scheduling |
Emergency replacements compress this schedule but rarely eliminate the permit and compliance steps. Our RTU replacement page describes how we sequence multi-unit portfolio replacements.
Frequently asked questions
Do I need a permit to replace a rooftop unit in Orange County?
Yes. Replacing a commercial RTU is permitted mechanical work in every Orange County jurisdiction.
Does the new unit have to meet current Title 24?
In most cases, yes. Replacement is treated as an alteration and the current code edition at the time of permit generally applies.
Who does acceptance testing?
A certified acceptance test technician. We coordinate this as part of the project so it does not delay final inspection.
Can you replace a unit with the same model?
Sometimes the same footprint and capacity can be matched, but efficiency, controls, and refrigerant requirements may force a different model.
Have a site this applies to?
Davinci Mechanical is the commercial and union division of Scottish Tom's Heating & Air. Send us the equipment list or the problem and we'll tell you what we'd check first.