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Nonresidential High Efficiency Boilers and Service Water Heating

Measure Description

This CASE Report will include two submeasures: high efficiency boiler systems and high efficiency service water heating equipment systems. Specifically, these submeasures will update the boiler efficiency and service water heating system requirements to harmonize with the requirements proposed for Addendum BC to ASHRAE Standard 90.1-2016 and section 7.5.3 of ASHRAE Standard 90.1-2016 respectively. To harmonize with the  ASHRAE proposal, this CASE Report will proposal increases to the minimum thermal efficiency for high capacity boilers (1,000,000 – 10,000,000 Btu/hr) to a weighted-thermal efficiency of 90 percent (90%Et), while section 7.5.3 requires the same 90%Et for gas service water heating systems.

Additionally, this CASE measure will harmonize with the design requirements for the hot water distribution systems for large boiler systems in Addendum BC as shown below.

  • Hot water return entering the boiler(s) be 120oF or less the temperature difference between the hot water supply leaving the boiler and the return to the boiler be 40oF or more.
  • Establish flow rate requirements for supply hot water that recirculates directly into the return system to ensure flow rates are slow enough that condensing occurs. The tentative requirements are that flow rates be no greater than a) 20 percent of the boiler system hot water flow rate at design conditions AND b) 5 percent above the sum of the minimum flow rates of operating boilers.

The ASHRAE proposal includes an exception that boiler systems do not need to meet the equipment efficiency or hot water distribution system design requirements if 25 percent of the annual space heating requirement is provided by site-solar energy, site-recovered energy, or heat recovery chillers or where half or more of the design heating load is served using perimeter convective heating, radiant ceiling panels, or both. The Statewide CASE Team will explore these exceptions and whether they would apply for California.

Provide Feedback

Participate in the Utility-Sponsored Stakeholder meeting for this topic on October 17th, 2019! View the event here.

This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email Include the measure name in the subject line.


Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.


Give Us Your Feedback

The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

  • Use the form above to provide feedback on this measure.