Residential HPWH Ventilation Clean Up
Measure Overview
This measure would simplify the four compliance pathways in the 2025 code to make HPWH installation decision making simpler, as well as improving consumer-sized HPWH performance in single family, multifamily and non-residential buildings.
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This measure page will be updated as the 2028 code cycle progresses. For questions or suggestions, submit feedback to [email protected]. Please include the measure name in the subject line.
View the Energy Commission's proceedings and available proposed code language by visiting their CEC 2028 Proceedings Website page.
Scope of Proposed Code Change
| Building Type(s) | Construction Type(s) | Type of Change | Updates to Compliance Software | Third Party Verification |
| Single family, multifamily, nonresidential | New construction, additions, alterations | Mandatory | Update existing feature | No changes to third party verification |
Justification for Proposed Change
The 2025 energy code was updated to include ventilation requirements for consumer-sized integrated HPWHs. Allowed methods of providing ventilation included those approved by manufacturer, installing in a large unvented room of minimum size, installing in a closet with minimum ventilation area, and directly ducting the unit. The CASE team recommends improvements to the code language for clarity and adjustments to requirements to reflect new research and better align with other codes in development. This measure also recommends eliminating two ducting configurations from the 2025 code: inlet air ducted from outside with no exhaust duct and exhaust ducted to outside with no inlet duct. These configurations interfere with the operation of balanced and central indoor air quality (IAQ) ventilation systems and increase space conditioning load.
The typical HPWH currently on the market, when installed and vented within conditioned space, presents minimal impact on space conditioning loads when the space is 450 cubic feet or larger. However, ducting only the HPWH inlet or only the HPWH exhaust to outside can negatively impact IAQ and increase heating and cooling load by bringing in as much as 200 cfm of unconditioned air while operating. In addition, inappropriately sized and uninsulated ducting for HPWHs can lead to moisture damage risk inside the conditioned space and/or other small water heater locations which is a health and safety concern. Updated code language in this measure would reduce IAQ issues, moisture damage risk and health and safety concerns by providing updated ventilation language.
Relevant Documents
Round One Utility-Sponsored Stakeholder Meeting Materials
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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.