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Residential Instantaneous Water Heaters

2016 Title 24 CASE Topics

Measure Overview

The Residential Instantaneous Water Heaters (IWH) measure proposes modifications to the prescriptive requirements for domestic water heating systems in single family homes and multi-family buildings with dedicated water heaters for each individual dwelling unit. The goal of the measure is to update the water heating energy budget to help ensure that builders are encouraged to improve the efficiency of hot water systems in residential buildings.

This measure builds upon the high-efficiency water heater (HEWH) ready measure that was adopted into the 2013 Title 24 standards (effective July 1, 2014). The HEWH standards require domestic water heating systems in new residential construction (single family and multi-family buildings with dedicated water heaters in individual dwelling units) to be designed to accommodate condensing gas storage and gas IWHs. By the time the 2016 Title 24 Standards take effect in 2017, builders will be accustomed to designing for higher-efficiency water heaters. High–efficiency water heaters have also been proven to be cost-effective in all climate zones across California.

Proposed Code Changes

The proposed code changes would modify the code requirements by specifying that the applicant can comply with the prescriptive standards by installing a gas instantaneous water heater (IWH) that meets minimum federal efficiency levels. As an alternative, the applicant can also comply by installing a gas storage water heater that meets federal minimum efficiency levels. If the applicant chooses to install a gas storage water heater, they will also be required to have a Home Energy Rating System (HERS) verified Quality Insulation Installation (QII), plus one of the following:  installation of a compact hot water distribution design or a HERS verified domestic hot water pipe insulation. Each of these options will result in approximately equivalent energy performance on a statewide basis; they were modeled using CEC’s approved public domain modeling software program, CBECC-Residential, Version 3 (see Section 5.1for projected savings of proposed prescriptive options).

The proposed prescriptive options are as follows:

  1. Install a single natural gas or propane IWH meeting minimum federal efficiency levels (used to calculate baseline energy budget for performance approach); or
  2. Install a single gas or propane storage water heater meeting minimum federal efficiency level plus with an input of 105,000 Btu per hour or less in combination with QII requirements (HERS verified) and either:
    1. Compact hot water distribution design that is field verified; or
    2. Pipe insulation requirements (HERS verified).

In addition, the Statewide CASE Team recommended adding a mandatory requirement that if a gas IWH is installed, a drain kit (i.e. isolation valves) must be installed as part of the water heating system. Isolation valves assist in the flushing of the heat exchanger and help prolong the life of gas IWHs. Installation of a drain kit has become the standard among installers and plumbers and is recommended by water heater manufacturers. These valves are typically not included with the water heater unit.

The Statewide CASE Team will also be recommending revisions to the Alternative Calculation Method Reference Manual and Residential Compliance Manual to improve how “gas availability” is defined, and how one determines “gas availability.

Stakeholder Meeting

Several stakeholder meetings and CEC staff workshops were held regarding the Nonresidential HVAC Economizer Modifications building energy efficiency topic. The list of past meetings and hearings can be found here. If you would like to receive email updates on this CASE topic, click the link below.


  1. Final CASE Report