The rooftop unit over your shop finally dies in August. Your contractor swaps it in two days, the space is cold again, and you assume that is the end of it. Then the inspector will not sign off, because nobody has produced a Certificate of Acceptance — a signed document proving the new unit's controls were actually tested after installation, not just wired up.
For commercial and hotel buildings in California, replacing or altering a heating and cooling system is not finished when it runs. Before an occupancy permit is granted, listed equipment and systems must be certified as meeting the acceptance requirements, and a Certificate of Acceptance must be submitted to the enforcement agency (§ 120.5). Alterations must also meet current energy standards (§ 141.0).
What has to be tested before sign-off
The list in § 120.5 is specific. Among the systems that must be tested and certified:
- Outdoor air ventilation systems
- Constant-volume, single-zone air conditioning and heat pump unit controls
- Duct systems, where the alteration rules require duct testing
- Air economizers and dedicated outdoor air, heat recovery and energy recovery systems
- Demand-control ventilation systems, where required
- Supply fan variable-flow controls
- Hydronic (hot- and chilled-water) system variable-flow controls
- Boilers or chillers requiring isolation controls
- Hydronic systems with supply-water temperature reset controls
- Automatic demand-shed controls
- Fault detection and diagnostics on packaged direct-expansion units
Before an occupancy permit is granted, the following equipment and systems shall be certified as meeting the Acceptance Requirements for Code Compliance.
The point of this list is that most of it is controls, not hardware. A rooftop unit can be correctly installed and still fail acceptance because its economizer never opens, or its demand-control ventilation sensor was never commissioned. That is exactly the failure the testing exists to catch, because nobody notices it — the space still heats and cools, it just wastes energy doing it.
Two carve-outs are written into the section: systems serving healthcare facilities are exempt from § 120.5 entirely, and a factory-calibrated, factory-tested air economizer certified to the Energy Commission does not have to repeat the functional test.
Altering an existing building
If you are not building new, § 141.0 is the section that governs you. Additions, alterations and repairs to existing commercial and hotel or motel buildings must meet the applicable mandatory requirements, plus either a prescriptive path or a performance path, for the climate zone the building sits in.
| Your project | Your two options |
|---|---|
| Addition | Prescriptive approach, or performance approach (energy budgets) |
| Alteration | Prescriptive approach, or performance approach (energy budgets) |
The prescriptive path is a checklist: the envelope, lighting, any newly installed space-conditioning, electrical power distribution or water-heating system, and any new sign must each meet the listed requirements. The performance path lets you model the building's energy use instead, which is how projects that cannot meet one item on the checklist trade it against something better elsewhere.
Two notes in that section are worth knowing. If an alteration changes the building's occupancy classification, the alteration requirements apply to the occupancy after the work. And alterations to healthcare facilities are not required to comply with § 141.0 at all.
The clean-air rules are optional unless your city adopts them
This is the distinction that trips people up when they read about air filtration requirements. The mechanical code contains a clean-air appendix, and it opens by saying so plainly: its provisions are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance (Appendix J).
Where a city does adopt it, the substance is concrete. In assembly, business, educational and institutional occupancies, each mechanical system must be sized to handle the design airflow at the static pressure drop of a supply air filter rated MERV 13 or better (Appendix J) — MERV being the standard scale for how much fine particulate a filter captures. Spaces where 100 percent of the supply air already passes through HEPA filtration are excepted.
So the honest answer to "does my building need MERV 13 filters?" is: not under the state mechanical code by itself. Ask your building department whether your city adopted the appendix. State code is a floor here, and local governments may adopt more restrictive standards.
What this means before you sign a contract
Three practical consequences follow from the sections above.
Budget for acceptance testing, and name it in the contract. It is a required deliverable before occupancy, not an optional commissioning extra, and it is far cheaper to assign it before the work than to chase it afterward.
A like-for-like swap is still an alteration. Replacing equipment pulls the work into § 141.0, which means the new equipment answers to today's standards rather than to whatever was legal when the old unit went in.
Check the climate zone. The compliance requirements in § 141.0 are climate-zone specific, so the same rooftop unit can pass in one part of California and fail in another.
What these sections do not tell you: the specific efficiency values your equipment must hit, or the test procedures themselves. Those live in the referenced appendices and tables the sections point at, and they are what your mechanical engineer or a certified acceptance test technician is reading.
