What Furnace Efficiency (AFUE) Does California Require?
Title 24 sets no furnace AFUE of its own. Efficiency comes from the federal and California appliance regulations in force when the permit is applied for. The 2025 compliance manual prints 80 percent AFUE for non-weatherized gas central furnaces under 225,000 Btu/h and 81 percent for weatherized ones; it lists no 90 or 95 percent minimum.
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Who sets the number
The efficiency of most heating equipment is regulated by the federal NAECA standard and the California Appliance Efficiency Regulations, which Section 110.1 references. Those regulations are published separately from the Energy Code. Manufacturers must certify equipment to the Commission before it may be installed (Section 110.2).
The permit-date rule
The compliance manual notes that the regulations in effect when the building permit is applied for decide the minimum efficiency of the appliances named in the compliance documents. A furnace ordered today is judged against that date, not the date it is installed. Predicting later changes is outside this page.
The minimums the manual prints
Table 4-1 of the 2025 Single-Family Residential Compliance Manual, which draws on Title 20 Tables E-5 and E-6, lists for gas central furnaces:
- Under 225,000 Btu/h, weatherized, single-phase: 81 percent AFUE.
- Under 225,000 Btu/h, non-weatherized, single-phase: 80 percent AFUE.
- 225,000 Btu/h and above: 81 percent thermal efficiency instead of AFUE.
These are the figures printed in the manual; check the specific model's certified listing before relying on them.
What Part 6 asks of the installation instead
- The furnace runs within the manufacturer's maximum temperature rise (Section 150.0(h)4A).
- Furnaces are sized using ACCA Manual S-2023, Table N2.5 (150.0(h)5B).
- Where the system also provides cooling, the air handler must show 0.45 W/cfm or less for a gas furnace, or 0.58 for units made before 3 July 2019 (150.0(m)13B and Exception 3).
- Furnaces of 225,000 Btu/h or more need an intermittent ignition device plus power venting or a flue damper (110.2(d)).
Checking a model
The Energy Commission lists certified appliances in its appliance regulations certification pages, cited below. For the work a swap triggers, see the furnace checklist, the fuel question on gas for gas replacement and wall and floor furnaces, which have their own table. Orders start at residential Title 24.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
The 2025 compliance manual prints 80 percent AFUE as the minimum for non-weatherized gas central furnaces under 225,000 Btu/h. The regulations in force on the permit application date decide.
Not by its own text. Section 150.2(b)1 sets no AFUE; the appliance regulations do.
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