Does Replacing Commercial HVAC Trigger Title 24?
Yes. Space conditioning is a regulated component, so replacing it is an alteration — addressed specifically by Section 141.0(b)2E for altered space-conditioning systems. Like-for-like is still an alteration.
Where the requirements come from
Three places, and knowing which is which saves argument at plan check. Mandatory controls sit in Sections 110.2 and 120.2 and apply regardless of compliance path. Prescriptive controls sit in Sections 140.4(f) and (n). Altered space-conditioning systems specifically are addressed by Section 141.0(b)2E.
So a replacement is not assessed against "the building" — it is assessed against the requirements that attach to the equipment being changed and the controls that go with it.
The economizer threshold
This is the number to establish first. Section 140.4(e) requires an economizer on air conditioners and heat pumps with a design total mechanical cooling capacity over 33,000 Btu/hr. Below it, no economizer requirement from that provision; above it, one applies — and an economizer brings its own acceptance test.
Because the threshold is on design capacity rather than on physical size, a modest-looking unit can cross it. It is worth checking against the schedule rather than assumed from the tonnage in conversation.
Ductwork, and why "it was sealed already" gets tested
Where a claim is made that an existing duct system was previously sealed, that is confirmed by field verification and diagnostic testing under Reference Nonresidential Appendix NA2. The documentation is the starting point for a test, not a substitute for one.
Acceptance testing follows the equipment
HVAC and heat pump acceptance testing is documented on NRCA-MCH-03-A, and where an economizer is involved the economizer controls carry their own test. Both are performed on site by a technician certified for mechanical acceptance testing, which makes the replacement a programme item as well as a purchase.
What decides how large the job is
Cooling capacity against the 33,000 Btu/hr line, how much ductwork is touched, and which controls the new equipment brings into scope. A single small unit swapped with no ductwork disturbed sits at the light end. A capacity increase with new ducting and new controls does not.