Can a New ADU Use a Gas Water Heater?
Yes, but only through the performance path. None of the prescriptive water heating options for a new detached ADU is gas or propane, and a gas heater also brings the electric-ready space and wiring of Section 150.0(n)1. An ADU made by converting existing conditioned space is an alteration, where Section 150.2(b)1H lists gas among the allowed choices.
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What the performance path asks of you
The software compares the design with a standard design built from the prescriptive package in Section 150.1(c)8 and Table 150.1-A. The Energy Commission says any water heaters may be modelled, but the building's energy budget is compared with that standard. The compliance manual adds that multiple water heaters generally adjust the credits, and the adjustment has to be offset elsewhere in the total energy budget.
The space you give up
Section 150.0(n)1 reserves a spot at least 2.5 by 2.5 feet and 7 feet tall for a future heat pump unit. That is 6.25 square feet, about 1.6 percent of a 400 square foot ADU. It needs a condensate drain no more than 2 inches above the heater base that drains without a pump, plus wiring set out on electric-ready requirements. Electric units, and heat pump units of any voltage, are not caught by the rule.
By project type
- Attached ADU or garage conversion (addition) with a second heater: a gas tankless of 200,000 Btu/h or less is not an addition-alone prescriptive option (Example 9-32). Section 150.0(n) still applies where the heater is in the added floor area, under Section 150.2(a) and the manual's chapter 5 (its chapter 10 says otherwise, so confirm).
- Conversion of existing conditioned space (alteration): gas or propane is allowed under Section 150.2(b)1H, with pipe insulation, and electric-ready does not apply.
Check gas service early
HCD says an ADU not created from existing space may be required to have a new or separate utility connection, and that HCD has no authority over gas or electric service issues. Confirm the utility will serve the unit before the design relies on gas.
The prescriptive options are on water heater requirements, the electric choices on ADU heat pump water heaters, and project types on the attached ADU page. See also the detached ADU report and the ADU page.
Common Title 24 Questions
- Do ADUs need Title 24 in California?
- What plans are needed for an ADU Title 24 report?
- How much does an ADU Title 24 report cost?
- How long does an ADU Title 24 report take?
- Does a garage conversion ADU need Title 24?
- Does a JADU need a Title 24 report?
Frequently Asked Questions
Only through the performance path, with the electric-ready provisions of Section 150.0(n). A tankless above 6.8 kBtu/h input also needs isolation valves with hose bibbs on both the cold and hot sides.
Yes. Section 150.0(n)1 and the alteration list in Section 150.2(b)1H treat natural gas and propane alike.
Explore ADU and JADU
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View all ADU and JADU guides → · Permits and Compliance · Title 24 guide