Can I use a 120V plug-in heat pump water heater in my ADU?

Yes, if your new ADU has one bedroom or less, or if it passes on the performance path. The 2025 Energy Code's prescriptive water heating options call for a 240-volt heat pump water heater, but Exception 2 to Section 150.1(c)8 allows a 120V heat pump water heater in its place for a new dwelling unit with one bedroom or less. For a larger new ADU, a 120V unit is not a prescriptive option and can only be used if your Title 24 performance model shows compliance.

Why 120V appeals in an ADU

A 240V heat pump water heater needs a dedicated 240V branch circuit. A 120V model connects to a 120V circuit per the manufacturer's instructions, which can ease the load on a small subpanel or help avoid a service upgrade. It also simplifies retrofits where running a new 240V circuit is hard.

The prescriptive options for a new ADU (150.1(c)8)

• Option A: a single 240V heat pump water heater with the tank in the garage or conditioned space, plus a compact hot water distribution system in climate zones 1 and 16 and a field-verified drain water heat recovery system in climate zone 16.
• Option B: a single 240V heat pump water heater meeting NEEA Advanced Water Heater Specification Tier 3 or higher, with added drain water heat recovery and tank location rules in climate zone 16.
• Option C: solar water heating with electric backup and a solar savings fraction of at least 0.7.
• Exception 1: an electric water heater with point-of-use distribution for new units of 500 square feet or less.
• Exception 2: a 120V heat pump water heater in place of the 240V unit in Options A or B, for new units with one bedroom or less.

Garage conversions and attached ADUs

The Energy Commission treats attached ADUs and conversions of unconditioned space, such as garages, as additions. If you add a water heater as part of an addition, Section 150.2(a)1D lists its own options: a single heat pump water heater that isn't outdoors, sits on a rigid insulated base of at least R-10, and has a qualifying communication interface; a NEEA Tier 3 or higher unit; or, for additions of 500 square feet or less, an electric point-of-use heater. Confirm with your Title 24 consultant how a 120V unit fits your project.

Practical trade-offs

• A 120V unit has less electrical power available for heating, so recovery is usually slower. Compare the first-hour rating with the ADU's real use: showers back to back, laundry, dishes.
• It still needs the same placement care as any heat pump water heater: enough air volume or venting (Energy Code 110.3(c)7), a condensate drain, a relief valve discharge, and seismic strapping.

What it means for your plumbing plan

The make, model, voltage, and capacity on your plumbing schedule must match the Title 24 compliance form, and the location, condensate route, and circuit must agree across the plumbing and electrical sheets. See how Title 24 affects water heaters, our Title 24 reports, and electrical load calculations.

Sources: energy.ca.gov, energy.ca.gov.