How does Title 24 affect HVAC?

Title 24 sets the minimum efficiency, the equipment type, the ventilation rate, and much of the design intent for your ADU's heating and cooling. In practice, it is the reason most new California ADUs are designed around an all-electric heat pump — the current prescriptive baseline for space conditioning in new construction.

What the energy code requires of HVAC

• Heat pumps as the baseline. Under the current code direction, heat pumps are the prescriptive baseline for space conditioning in new dwelling units, which is why ductless mini-split heat pumps dominate ADU design.
• Minimum efficiency ratings. Equipment must meet California's minimum efficiency requirements (expressed in metrics like SEER2/HSPF2 for the applicable cycle). The model numbers on your plans must meet or exceed those minimums.
• Mechanical ventilation. Title 24 incorporates whole-dwelling ventilation requirements (per ASHRAE 62.2), typically met with a continuous-operation bath fan, an ERV/HRV, or supply ventilation through the air handler.
• Duct and refrigerant verification. When ductwork exists, duct leakage and other measures may require HERS verification (documented on the CF3R).

How it shows up on your plans

The CF1R establishes the efficiency floor; your mechanical plans then have to reflect it. The mechanical equipment schedule lists the indoor and outdoor unit make/model/capacity and efficiency ratings, the ventilation fan CFM, and electrical requirements — and the plan checker compares that schedule against the Title 24 numbers. If the equipment specified on the plans falls below the efficiency the CF1R assumed, the plans receive a correction.

Prescriptive vs. performance for HVAC

On the prescriptive path your equipment must individually meet the minimum efficiency. On the performance path, energy modeling can let a slightly different system pass if the whole-building design still meets or beats the baseline — useful when site or space constraints push you off the standard solution.

A practical example: an 800 SF one-bedroom ADU designed with a single-zone ductless mini-split heat pump, sized from a Manual J load calculation, paired with a continuously running bath fan delivering roughly 30–40 CFM for ventilation. That combination is the cleanest route through Title 24 for most projects.

Many cities have also adopted all-electric reach codes that prohibit gas furnaces in new ADUs — another reason heat pumps are the default. The applicable code cycle and local amendments vary, so confirm with your local building department. We coordinate the CF1R efficiency assumptions with your mechanical sheets, available as a +$240 Title 24 add-on alongside your MEP package.