Process Boiler #1 Non-condensing Stack Economizer Requirement
Measure Overview
This proposal would require boiler stack (non-condensing) economizers on process boilers with capacities at or above 5 MMBtu/hr. The requirement would apply to all new process boilers, including replacement boilers and boilers in additions to existing facilities. Boilers with stack temperatures below 350° F at lowest firing rate would be exempt from this requirement.
The Statewide CASE Team is evaluating two additional potential exemptions for the requirement:
- Boilers that burn combustible fuels that have high potential for fouling in the heat exchanger, such as woody biomass.
- Sites where the retrofit building ceiling height or existing footprint shape results in insufficient room to install a standard boiler plus stack economizer combination.
Boilers used in oilfield production and utility and municipal power generation are not expected to be within the scope of Title 24, Part 6. Table 1 summarizes the scope of the proposed code change.
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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 |
| Nonresidential | New construction, additions, alterations | Mandatory | No updates | Add new verification requirements |
Justification for Proposed Change
Most steam boilers lose 20% or more of their input fuel energy in the form of combustion exhaust. A stack economizer, which is an assembly of finned tubing placed in the boiler exhaust stream, can recover a significant fraction of this waste heat by preheating the boiler feedwater with the hot boiler flue gas. This reduces load and thermal stress on the boiler, lowers fuel consumption, and extends boiler useful life.
The use of boiler stack economizers has been listed in Department of Energy literature as a best practice since at least the early 2000s. Despite its cost-effectiveness, this measure often goes unimplemented because of its first cost and the general lack of owner and operator awareness of the energy benefits. In general, boiler system vendors and contractors are highly familiar with this technology, and it is widely available. Stack economizers can be installed in various configurations, including roof boxes, making them feasible in most facilities.
The use of a stack economizer is typically the highest-impact action that sites can take to reduce their boiler natural gas usage, saving 2-3% of fuel energy by preheating boiler feedwater. Preliminary statewide natural gas savings from a stack economizer requirement are estimated at 1.37 million therms per year.
Additional benefits of this proposed code change include job creation in the manufacturing and installation of stack economizers, as well as improved local air quality. Many industrial facilities are located near Low- and Moderate-Income (LMI) housing, which is disproportionately exposed to lower air quality. This proposal would reduce photochemical smog in these communities.
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.