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Multifamily Domestic Hot Water

Measure Description

This CASE Report for multifamily domestic water heating will include three submeasures: central heat pump water heating, hot water distribution, and solar thermal water heating.

Central Heat Pump Water Heating

This submeasure will develop a prescriptive compliance pathway for domestic central heat pump water heating systems to encourage implementation in multifamily buildings by leveraging existing software algorithm development, lab testing, and design guide development. The CASE Team will perform additional market readiness research across a broad group of stakeholders and develop code and compliance manual language.

Hot Water Distribution

The 2013 Multifamily Central Domestic Hot Water and Solar Thermal CASE Report estimated that 33 percent of hot water generated at the water heater is lost in the recirculation loop to ambient space. As a result of the 2013 CASE Report, currently Title 24, Part 6 prescriptively requires demand control recirculation, as well as a minimum of two recirculation loops in multifamily buildings that have nine or more dwelling units.  This  submeasure will further reduce the performance budget of multifamily domestic hot water recirculation systems and will include modifying prescriptive pathways, refining the HERS test procedure, and updating the Alternative Calculation Method Reference Manual calculations. The sub measure will allow one of three compliance options or alternate prescriptive paths.

  • Increase the number of recirculation loops per multifamily building to three or more or assign a maximum loop length. Increase the insulation requirements on distribution piping and/or require a radiant barrier on distribution piping currently subject to insulation requirements.
  • Install trace heating. Trace heating involves placing linear electrical resistance heating elements directly in contact with distribution piping, covered with insulation, to keep the pipe and water warm. Aside from reducing demand at the water heater, heat trace would also eliminate the need for a recirculation loop and the associated pump power and distribution losses from the return pipe.

Solar Thermal Water Heating

This submeasure will investigate options to expand solar thermal water heating requirements for new high-rise and low-rise multifamily buildings for individual/central gas water heaters and individual/central heat pump water heaters. The Statewide CASE Team will evaluate energy savings and cost-effectiveness of the following solar water heating measures.

  • Increasing the SSF prescriptive requirement of solar thermal water heating for central gas and propane water heating systems.
  • Add requirement of solar thermal water heating for individual gas and propane water heaters. This approach may not be cost-effective, but will reduce associated greenhouse gas (GHG), and could be an alternative compliance pathway.
  • Develop prescriptive SWH requirement for central heat pump water heaters.
  • Evaluate an option to combine solar thermal system with individual heat pump water heater. This option may not be cost effective for multifamily buildings due to potential high first cost. The Team will survey subject matter experts (SME) to confirm.

Provide Feedback

Participate in the Utility-Sponsored Stakeholder meeting for this topic on October 3rd, 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.