Can a new ADU use electric baseboard heat?

Not prescriptively. Table 150.1-A shows electric resistance space heating not allowed in all 16 zones, apart from a supplemental heater of up to 2 kW with a 30-minute time limit. A performance model is the only route for baseboard.

Which Energy Code applies to an ADU permit filed in 2026?

The 2025 Energy Code applies to permit applications submitted on or after 1 January 2026. The building department sets the application date.

ADU Heat Pump Requirements in California for 2026 Permits

A newly constructed detached ADU is steered to a heat pump: Section 150.1(c)6 makes it the prescriptive space-conditioning system, and anything else must pass the performance model. Attached ADUs and garage conversions are additions, and converted existing rooms are alterations; both follow Section 150.2, where the rules turn on whether the system is new or extended.

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Detached ADU: the package assumes a heat pump

For permit applications submitted on or after 1 January 2026, Table 150.1-A shows heat pump heating at the minimum HSPF2 and SEER2 in all 16 climate zones, with electric resistance heating not allowed and gas heating marked NA. Another system complies only if the performance model offsets it, because the standard design the software builds already contains the heat pump. The general rules are on the heat pump requirements page.

Sizing rules that follow the equipment

Section 150.0(h) calls for a load calculation using ASHRAE, SMACNA or ACCA Manual J, with indoor design temperatures of 68 degrees F for heating and 75 degrees F for cooling. Selection follows ACCA Manual S-2023: heating capacity must meet the building code minimum without counting supplementary heat, and there is no maximum. Additions may use block loads (load calculations).

Allowances for small units

The 90-minute defrost delay is waived in zones 6 and 7 for any dwelling, and in zones 3, 5 to 10 and 15 for a dwelling of 500 square feet or less.
Backup heat locks out above 35 degrees F, but buildings under 500 square feet, and buildings of any size in zones 7 and 15, may use the alternative controls in Exception 1 to Section 150.0(h)7.

Attached ADUs and conversions

When heating is extended from the house's existing system, that equipment need not meet Part 6 (Exception 3 to Section 150.2(a)). A shared system still cannot return air from one dwelling unit to another, the ADU needs its own thermostat, and the manual notes that systems without ducts are an option; the attached ADU page explains why. A new system serving an addition meets the new-home space-conditioning rules (Example 9-11). In an alteration, Section 150.2(b)1G bars electric resistance as the primary heat source, with exceptions where the existing heat is already electric resistance. The ductless route is covered in can an ADU use a mini-split.