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Multifamily Domestic Hot Water

Measure Description

​Domestic Hot Water (DHW) Distribution

There are three separate DHW distribution submeasures: pipe insulation verification, increased insulation, and California Plumbing Code (CPC) Appendix M sizing. The pipe insulation verification submeasure stems from observation of poor quality of existing insulation by the 2013 Public Interest Energy Research (PIER) Report “Multifamily Central Domestic Hot Water Distribution Systems.This study motivates the pipe insulation verification submeasure by the poor quality of existing insulation exhibited by the study and design firms and stakeholder feedback during the CASE Process (PIER 2013). This submeasure is similar in scope and mechanism to the existing multifamily quality insulation installation (QII) energy credit through Home Energy Rating System (HERS) or Acceptance Test Technician (ATT) verification and would apply to multifamily buildings with recirculation systems.  

The increased pipe insulation submeasure builds on the 2013 Water and Space Heating ACM Improvement CASE Report (Statewide CASE Team 2011), that analyzed and showed increasing DHW pipe insulation to be cost-effective. The 2013 CASE effort did not result in an increase in pipe insulation level in the code because the increased insulation level for heating ventilation and air conditioning (HVAC) was not cost-effective, and insulation level requirements for both DHW and HVAC pipes are codified in the same code Table, 120.3-A. 

The CPC Appendix M sizing submeasure would introduce a performance-based pipe sizing calculation procedure from Uniform Plumbing Code (UPC) and CPC into Title 24, Part 6.  

Additionally, current prescriptive requirement for two-loop recirculation systems faces compliance and enforcement challenges including inconsistent interpretations of the requirement and challenges establishing appropriate baseline and proposed systems in the compliance software.

Drain Water Heat Recovery (DWHR)

DWHR utilizes a heat exchanger in the shower drain line to recover waste heat using the reclaimed heat to pre-heat coldwater supplied to the cold-water side of the shower or/and the water heater. The 2019 DWHR CASE Report concluded that DWHR were not cost-effective for low-rise multifamily buildings in all climate zones when four or more dwelling units share one DWHR device (CASE 2017) . Subsequently DWHR became a compliance option for the 2019 Title 24, Part 6 code. 

The proposed DWHR measure would have prescriptively required DWHR in all new construction multifamily buildings for all hot water system types. However, the Statewide CASE Team found that the measure is not cost effective due to HCD water meter requirements. The Statewide CASE Team requested an exception from HCD, which HCD denied. If HCD grants an exception for DWHR devices then the measure is cost effective and could be implemented in Title 24, Part 6 as described in the following paragraph.  

Prescriptive requirements for DWHR depend on hot water distribution type (central or individual), heat recovery installation (equal or unequal flow), and DWHR location (in drain line serving multiple dwelling units or in drain line serving one dwelling unit) 

Solar Water Heating

Solar water heating systems utilize roof-mounted flat-pate solar collectors with glycol as a working fluid to pre-heat the domestic water system. This measure builds on existing solar water heating requirements for central DHW systems and assesses the technical and economic feasibility of higher solar savings fractions.  

The solar water heating measure would have extended existing prescriptive requirements for solar thermal water heating to other water heating system types for newly constructed multifamily buildings.  The proposal would impact newly constructed multifamily buildings no greater than ten stories in height. The proposed requirement would increase the minimum required size of a solar water heating system to meet at least 50 percent of the annual water heating load for the building. The Statewide CASE Team found that the measure is not cost-effective. 

Central Heat Pump Water Heating

This measure will develop a prescriptive compliance pathway for central domestic water heating systems with heat pump technology serving multiple dwelling units by leveraging existing software algorithm development, lab testing, and design guide development. The Statewide CASE Team will perform additional market readiness research across a broad group of stakeholders and develop code and compliance manual language. This measure was initially included within the Multifamily Domestic Hot Water CASE report, but under advisement from the Energy Commission, the Statewide CASE Team moved to it to the Multifamily All Electric Package CASE Report.

Relevant Documents

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

Round Two Utility-Sponsored Stakeholder Meeting Materials

Round One Utility-Sponsored Stakeholder Meeting Materials

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Draft CASE Report Now Available (Comments accepted until June 26, 2020)

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.


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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.

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