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Earlier editions: 20222019

Chapter 12 — HYDRONICS

1203.2 Dual Purpose Water Heaters — 2025 California Mechanical Code

California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-09-25 · California

CBSC: official editions, supplements and errata

Italicized text is a California amendment to the model code, as printed in the official publication.

Cite as: 2025 California Mechanical Code (Title 24, Part 4) § 1203.2 · Effective January 1, 2026 · Official source: Building Standards Commission

Water heaters utilized for combined space-heating and water-heating applications shall comply with the standards referenced in Table 1203.2, and shall be installed in accordance with the manufacturer’s installation instructions. The total heating capacity of a dual purpose water heater shall be based on the sum of the potable hot water requirements and the space heating design requirements corrected for hot water first-hour draw

recovery.

TABLE 1203.2

WATER HEATERS

TYPE STANDARDS


Gas-Fired, 75 000 Btu/h or less,
Storage		 CSA/ANSI Z21.10.1/CSA 4.1



Gas-Fired, Above 75 000 Btu/h,
Storage and Instantaneous		 CSA/ANSI Z21.10.3/CSA 4.3


Electric, Space Heating		 UL 834


Solid Fuel-Fired		 UL 2523

For SI units: 1000 British thermal units per hour = 0.293 kW

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▸Contents — California Mechanical Code (Title 24, Part 4)
California Mechanical Code (Title 24, Part 4)

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