What electrical circuits do heat pumps need in an ADU?

Each heat pump appliance generally gets its own dedicated branch circuit, sized from the equipment nameplate's minimum circuit ampacity and maximum overcurrent protection, and outdoor units need a disconnect within sight. In most ADUs that means a circuit for the mini-split or ducted heat pump and one for the heat pump water heater, and the 2025 Energy Code allows a 120-volt heat pump water heater in place of a 240-volt unit in a new dwelling with one bedroom or less.

Space heating and cooling

• Size from the nameplate. Heat pump and air-conditioning equipment lists a minimum circuit ampacity and a maximum overcurrent protective device rating. The wire is sized from the first, and the breaker can't exceed the second.
• Disconnect. Section 440.14 requires the disconnecting means to be within sight of the equipment and readily accessible, with proper working space in front of it. A disconnect installed tight behind the condenser with no room to work violates the rule.
• Indoor units. On many ductless systems the indoor heads are powered through the outdoor unit's wiring, while some ducted air handlers need their own circuit. Follow the manufacturer's installation instructions.
• Service receptacle. The code requires a receptacle near heating and cooling equipment so technicians can plug in tools.
• Extras. Condensate pumps and backup electric heat strips, if used, add circuits or load.

Water heating

The 2025 Energy Code's prescriptive path for new dwellings calls for a single 240-volt heat pump water heater, with two exceptions that help small ADUs:

• A new dwelling unit with one bedroom or less may use a 120-volt heat pump water heater instead of a 240-volt unit.
• A new dwelling unit of 500 square feet or less may use an electric water heater with point-of-use distribution meeting the Reference Appendix.

A 120-volt unit changes the circuit and can ease pressure on the panel, but it has to be wired exactly as its listing and instructions require. Other water heating choices can be evaluated through the performance approach in your Title 24 report.

How heat pumps show up in the load calculation

Because heating and cooling from the same heat pump don't run at the same time, the load calculation counts the larger of the two rather than both. The water heater, cooktop, dryer and any EV charger are added on top, and together they decide how large the ADU panel and feeder need to be.

What this means for your electrical plan

The panel schedule should list every heat pump circuit with breaker and wire sizes taken from the equipment schedule, and the plans should show each disconnect and service receptacle. That only works when the mechanical and electrical drawings use the same equipment. See mini-split heat pumps for ADUs, choosing an ADU water heater and ADU panel sizing.

Sources: energy.ca.gov, energy.ca.gov, dgs.ca.gov, forums.mikeholt.com.