Under the 2025 California Energy Code, a new home, a new detached ADU or an addition with its own water heater normally gets a heat pump water heater (HPWH). The code also sets rules for where the tank goes, how much air it needs, and what to wire for the future if you install gas instead.
These rules apply to permit applications submitted on or after January 1, 2026. Sources are the 2025 Energy Code and Chapter 5 of the CEC's Single-Family Compliance Manual.
What does Title 24 require for a new home's water heater?
Section 150.1(c)8 gives three prescriptive options:
- A single 240-volt HPWH with the storage tank in the garage or conditioned space. Climate zones 1 and 16 also need a compact hot water distribution design. Zone 16 also needs a field-verified drain water heat recovery system.
- A single 240-volt HPWH that meets NEEA Tier 3 or higher. No extra features are needed in zones 2 through 15. Zone 16 needs drain water heat recovery and a garage or indoor tank.
- A solar water heating system with electric backup and a solar savings fraction of at least 0.7.
If you add hot water recirculation, only demand recirculation with manual on/off control is allowed.
Anything else, including a gas water heater, is allowed only through the performance approach. The compliance manual says such a system "can be installed using the performance approach," where the software compares your home with one built to the prescriptive rules.
What is NEEA Tier 3?
The Northwest Energy Efficiency Alliance (NEEA) writes an Advanced Water Heating Specification with performance tiers. The CEC says an HPWH that meets Tier 3 or higher "performs significantly better in real world conditions" and can meet the prescriptive requirement for new buildings, additions and alterations.
NEEA publishes a Residential Heat Pump Water Heater Qualified Products List. Check the exact model number there before you buy. In the performance approach, Tier 3 and Tier 4 units also earn compliance credit.
Separately, HPWHs certified to Joint Appendix JA13 for demand management can earn a performance credit. The CEC keeps a list of JA13-certified models, and a mixing valve is required with them.
Are there exceptions for small ADUs?
Yes, two:
- 500 square feet or less: a new dwelling unit may use an electric water heater with point-of-use distribution, as defined in Reference Appendix RA4.4.5 (Exception 1). The CEC's ADU FAQ says the same option exists for ADU additions of 500 square feet or less.
- One bedroom or less: a 120-volt HPWH may be used instead of a 240-volt one (Exception 2).
Point-of-use means short pipe runs. The CEC's ADU FAQ gives an example: up to 15 feet of 3/8-inch pipe or 10 feet of 1/2-inch pipe.
What about an addition or a garage conversion?
Section 150.2(a)1D applies only "when an additional water heater is installed as part of the addition." If it is, the choices are:
- A single HPWH, not located outdoors, on a rigid insulated surface of at least R-10, with a demand-response communication interface (Section 110.12(a) or an ANSI/CTA-2045-B port).
- A single HPWH that meets NEEA Tier 3 or higher.
- For additions of 500 square feet or less, an electric water heater with point-of-use distribution.
Gas is not on the prescriptive list for additions. Replacing an existing water heater is an alteration with its own list, which includes gas. See When is Title 24 required? for those rules.
Where can the heat pump water heater go?
For a new home, the prescriptive options put the tank in the garage or conditioned space. For an addition, it cannot be outdoors.
Every HPWH must also meet the mandatory rules in Section 110.3(c)7:
- Backup heat. Required when the unit draws unconditioned air, unless the compressor keeps working below the local Heating Winter Median of Extremes temperature listed in Joint Appendix JA2.
- Enough air. Pick one of four methods. Use the manufacturer's method, if it performs at least as well. Or give the unit a room of at least 100 cubic feet per kBtu/h of compressor capacity. Or vent it to a larger space with louvers sized at 125 square inches plus 25 square inches per kBtu/h. Or duct it.
The compliance manual works an example. A unit with a 4 kBtu/h compressor needs a 400 cubic foot room, or 225 square inches of louvered openings, or ducting. Use the manufacturer's number if it is larger.
The manual also warns that an HPWH in a confined closet without ducting can overcool the air and lose much of its efficiency.
I want gas. What does electric-ready mean?
If a new home uses a gas or propane water heater, Section 150.0(n)1 requires a space at least 2.5 by 2.5 feet and 7 feet tall for a future HPWH.
If that space is within 3 feet of the water heater:
- A dedicated 125-volt, 20-amp receptacle within 3 feet of the water heater, fed by a 120/240-volt, 3-conductor branch circuit rated at least 30 amps.
- The unused conductor labeled "spare" at both ends.
- A reserved breaker space next to it, labeled "Future 240V Use."
- A condensate drain no more than 2 inches above the base of the water heater that drains without a pump.
If the space is more than 3 feet away:
- A dedicated 240-volt, 30-amp branch circuit within 3 feet of the space, with a blank cover marked "240V ready."
- A reserved double-pole breaker space marked "For Future 240V use."
- Cold and hot water piping routed through the future HPWH location, exposed and easy to reach.
- The same condensate drain rule.
The manual says these rules apply to new buildings and to additions that get a water heater, not to alterations.
Where does this show up in my Title 24 report?
The CF1R lists the water heater type the design is based on. If the report assumed a NEEA Tier 3 unit, the plumber must install a listed model, and it must match the plans. For a new detached ADU, see Title 24 for ADUs for the other new-home rules.
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Frequently asked questions
Does a new California home have to use a heat pump water heater?
Under the prescriptive rules, yes, or a solar water heating system with electric backup. Other systems, including gas, can be used only through the performance approach, where the rest of the home has to make up the difference.
What is NEEA Tier 3?
A performance tier in the Northwest Energy Efficiency Alliance's Advanced Water Heating Specification. The CEC says a heat pump water heater rated Tier 3 or higher can meet the prescriptive requirement for new buildings, additions and alterations. NEEA publishes a qualified products list.
Can a heat pump water heater go in a closet?
Yes, if it gets enough air. Section 110.3(c)7 requires one of four options: a room of at least 100 cubic feet per kBtu/h of compressor capacity, louvered openings to a larger space, ducting, or a manufacturer's method that performs at least as well.
Can a small ADU use a 120-volt heat pump water heater?
Yes, if it is a new dwelling unit with one bedroom or less. Exception 2 to Section 150.1(c)8 allows a 120V heat pump water heater in place of a 240V one.
What if I install a gas water heater in a new home?
Section 150.0(n) requires a space at least 2.5 by 2.5 feet and 7 feet tall for a future heat pump water heater, with wiring, a condensate drain and, in some layouts, plumbing routed through that space.
Related
Sources
- energy.ca.gov/sites/default/files/2026-07/CEC-400-2025-010-F.pdf
- energy.ca.gov/filebrowser/download/8637?fid=8637
- energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/energy-code-support-center-6/2025
- neea.org/resource-type/product-specifications-qualified-products-lists/
- energy.ca.gov/rules-and-regulations/building-energy-efficiency/manufacturer-certification-building-equipment/ja13