California's 2025 Title 24 Part 6 cycle shifts the energy budget calculation to favor heat pump space and water heating more heavily than previous cycles, which means more contractors are running full Manual S heat pump selections who may not have needed to under earlier, more gas-equipment-centric code assumptions. Heat pump sizing carries real complexity beyond a standard gas furnace or straightforward AC selection, and getting it right matters both for code compliance and for actual system performance once installed.
Unlike gas furnaces, whose heating output stays relatively constant regardless of outdoor temperature, a heat pump's heating capacity decreases as outdoor temperature drops. This means the same piece of equipment delivers meaningfully different heating output depending on the day's weather — a heat pump that comfortably meets a home's heating load at 40°F outdoor temperature may fall well short of that same load at 20°F, depending on the specific unit and climate zone.
Every heat pump has a balance point — the outdoor temperature below which its heating capacity alone can no longer meet the building's full heating load. Below that point, supplemental heat (electric resistance, or a backup gas furnace in a dual-fuel configuration) is needed to maintain comfort. Manual S selection for heat pumps requires identifying this balance point specifically for the equipment and climate zone under consideration, rather than assuming standard-condition capacity applies year-round.
Because Manual J produces separate heating and cooling loads, and heat pump capacity behaves differently across outdoor conditions for each, equipment selection sometimes has to prioritize one load over the other depending on climate. In heating-dominated climate zones, selection generally prioritizes heating capacity matching, potentially resulting in a unit that's oversized for cooling; in cooling-dominated zones, the reverse consideration applies. This trade-off needs to be a deliberate decision within Manual S, not an accidental byproduct of nominal-size selection.
The 2025 cycle's energy budget calculation weights heat pump equipment more favorably in the overall compliance calculation than gas equipment, which means a project's compliance path increasingly depends on accurate heat pump sizing and selection rather than defaulting to gas systems that carried a favorable calculation under earlier cycles. This shift means Manual J and Manual S accuracy has become more directly tied to Title 24 compliance outcomes than it was previously, not just to comfort performance.
Where a heat pump's balance point falls above the coldest design temperature for a project's climate zone, supplemental heat needs to be sized and documented as part of the overall system design — either electric resistance backup sized to cover the remaining load below the balance point, or a dual-fuel configuration with a backup gas furnace. Both approaches need to be reflected accurately in the compliance calculation, not left as an unaddressed gap in the documentation.
Does every heat pump need supplemental heat in every climate zone?
Not necessarily — in milder climate zones, a correctly selected heat pump may cover the full heating load without a balance point issue arising within the local design temperature range. Colder zones are where supplemental heat considerations become more consistently relevant.
How does dual-fuel (heat pump plus gas backup) selection affect Title 24 compliance?
It depends on the specific cycle's energy budget calculation, since dual-fuel systems combine electric and gas equipment in a way that the compliance software evaluates based on expected usage split between the two — this needs to be modeled accurately rather than assumed.
Is heat pump selection under Title 24 meaningfully different from standard Manual S elsewhere?
The underlying Manual S process is the same, but the 2025 cycle's energy budget weighting makes accurate heat pump capacity data and balance point analysis more consequential to the compliance outcome than in previous cycles or in states without similar electrification-focused provisions.
Psychro.Pro prepares Manual S heat pump selections that account for balance point, supplemental heat, and Title 24's energy budget calculation together.Learn more.
