Do I need Title 24 to add a mini-split?

Yes. It is a new space-conditioning system in an existing home. There is no duct test, but a heat pump mini-split needs refrigerant charge verification in every climate zone.

Do I have to install a heat pump instead of an air conditioner?

Not under the statewide Energy Code. Some cities and counties adopt local reach codes that go further, so check with your building department.

What if my old ducts fail the leakage test?

Where existing ducts are kept, sealing every accessible leak and confirming it by visual inspection and smoke test is the accepted fallback when 10 per cent total or 7 per cent to outside cannot be reached. An entirely new duct system has to reach 5 per cent.

Will adding central air mean more attic insulation?

Only if an entirely new duct system goes in a vented attic or the ceiling is altered. Then R-49 applies in most zones, unless the attic already has R-38.

Does Adding Central Air Need Title 24?

Yes. Adding cooling to a house that has none is an alteration under §150.2(b) of the Energy Code, and what it triggers depends on what you install. A coil and outdoor unit on your existing furnace brings duct sealing and, in many zones, refrigerant charge checks. An entirely new ducted system must meet the new-system rules, including duct leakage of 5 per cent or less.

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Three ways to add cooling

Most projects are one of these, and the Energy Code treats them differently:

Adding to the existing furnace. A cooling coil goes on the furnace, an outdoor unit goes outside, and the existing ducts carry the air.
An entirely new ducted system. A new air handler, new heating and cooling equipment and a new duct system.
Ductless. One or more mini-split units with no ductwork.

Replacing a system you already have is a different question, answered on does an HVAC replacement need Title 24.

Adding cooling to an existing furnace

Installing a cooling coil or an outdoor condensing unit is one of the named triggers in §150.2(b)1E. The ducts connected to it must be sealed and tested by an ECC-Rater to one of these results:

total leakage of 10 per cent or less of the air handler airflow
leakage to outside of 7 per cent or less
if neither can be reached, every accessible leak sealed and confirmed by visual inspection and a smoke test

The test is not required where the duct system has less than 40 linear feet of duct, has already been sealed and verified, or is constructed, insulated or sealed with asbestos. Ducts, coils or air handlers in a garage have a 6 per cent target of their own.

Because the project adds refrigerant components, §150.2(b)1F applies as well. In every zone, the thermostats on the system must be replaced with setback thermostats. An air conditioner in zones 2 and 8 to 15 also needs its refrigerant charge verified and a measured airflow of at least 300 cfm per ton. If more than 25 feet of new duct is added to reach new rooms, the new ducts in unconditioned space need R-6 or R-8 insulation depending on zone.

An entirely new ducted system

A system counts as entirely new when the air handler and all the heating and cooling equipment are new and so is the duct system, meaning at least 75 per cent new duct material. A house that never had ducts is normally in this group. It has to meet much of what a new home meets:

a heating and cooling load calculation to ASHRAE, SMACNA or ACCA Manual J, using 68°F indoors for heating and 75°F for cooling, with equipment sized under ACCA Manual S
duct leakage of 5 per cent or less of air handler airflow
duct insulation of R-6 in zones 3 and 5 to 7, and R-8 in the other zones, for ducts in unconditioned space
airflow of at least 350 cfm per ton, and fan efficacy of 0.45 W/cfm or less for a gas furnace air handler or 0.58 W/cfm for other air handlers, both field verified
a static pressure probe or test hole in the supply plenum, and the air filtration requirements
refrigerant charge verification where Table 150.1-A requires it
an outdoor unit at least 5 feet from any dryer vent outlet

If the air handler and ducts go in a vented attic, the attic rules come with them: R-49 ceiling insulation in most zones, air sealing and covered recessed lights, unless the attic already has R-38. Those are set out on Title 24 insulation requirements.

Ductless mini-splits

A mini-split avoids the duct test and the duct insulation entirely. If it is a heat pump, heating as well as cooling, it needs refrigerant charge verification in every climate zone; a cooling-only unit needs it in zones 2 and 8 to 15. Where the standard procedure cannot be used, the installer weighs in the charge and an ECC-Rater verifies it.

Air conditioner or heat pump

The statewide code does not require a heat pump when you add cooling to an existing home. The Energy Commission lists a heat pump in place of an air conditioner in existing single-family homes as a voluntary CALGreen measure that cities and counties may adopt, so check your jurisdiction.

One rule can decide it. If the home has ducted electric resistance heat and the project replaces that heating while installing ducted cooling, the new heating cannot be ducted electric resistance, except in zones 7 and 15. The trade-off runs the other way on verification: in zones 1, 3 to 7 and 16 an air conditioner needs no refrigerant charge check, but a heat pump does. The detail is on Title 24 heat pump requirements.

The paperwork and the rater

The Title 24 documents go in with the permit application to your building department. The Certificate of Compliance lists the measures that need verification, the installer completes the Certificate of Installation, and an ECC-Rater tests the ducts, charge and airflow and registers the results with an ECC-Provider data registry such as CHEERS. The rater was called a HERS rater until 1 January 2026; the tests did not change.

Book the rater before anything is closed up. The duct test needs the ducts reachable and the system running. We prepare the alteration report as a permit-ready PDF by email, with unlimited revisions until you comply.