Can I Replace a Gas Furnace With a Gas Furnace in California?
Yes. Title 24's alteration rules let a house replace a gas furnace with a gas furnace. The fuel rule only bars electric resistance as the primary heat, so gas or a heat pump are the options. Longer-term limits come from air-district rules and local reach codes, which sit outside the Energy Code.
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What the Energy Code says about fuel
Section 150.2(b)1G says altered or replacement space heating shall not use electric resistance as the primary heat source. Nothing in Section 150.2(b)1 bars a gas furnace as the replacement, and the manual's Example 9-38 states that prescriptively the new heating unit must be natural gas fueled or a heat pump. Example 9-42 refuses a freestanding gas furnace swapped for an electric wall heater: the only electric option is a heat pump.
What a gas swap still triggers
- Minimum efficiency, which every unit sold in California already meets (Example 9-38).
- Duct sealing and verification under Section 150.2(b)1E, covered on the furnace checklist.
- A setback thermostat, but only when the system includes cooling and the existing thermostat is not already a setback type.
What does not follow the furnace
The heat-pump-ready wiring rule, a 240-volt circuit within 3 feet of a gas furnace and a reserved double-pole breaker space, is Section 150.0(t) and is written for newly constructed buildings. Section 150.2(b)1 lists 150.0(a) to (l), (m)1 to (m)10, (p) and (q) for alterations, so a replacement furnace in an existing house does not carry it.
Air districts and reach codes are a separate layer
The Bay Area Air Quality Management District lists Rule 9-4 as a zero-NOx standard for residential furnaces with a 2029 compliance date. South Coast AQMD's board voted 7 to 5 on 6 June 2025 not to approve amended Rules 1111 and 1121, the zero-emission furnace and water heater sales targets. Both are outside Title 24, and rules change, so ask your air district before ordering equipment. Cities can also adopt stricter energy standards with Commission approval under Section 10-106; see what a reach code is.
When a heat pump is worth pricing
If you are open to electric heat, a heat pump is the allowed electric choice; compare it in whether a heat pump is required and the heat pump checklist. Gas water heaters have their own air-district story on the water heater page. Reports for a swap start at residential Title 24.
Common Title 24 Questions
- What is Title 24?
- Do I need a Title 24 report?
- How much does a Title 24 report cost?
- How long does a Title 24 report take?
- What is included in a Title 24 report?
- What plans do I need to upload?
Frequently Asked Questions
Not in the Title 24 alteration rules read for this page. Section 150.2(b)1G restricts electric resistance as primary heat; it does not prohibit gas.
Section 150.0(t) applies to newly constructed buildings, and Section 150.2(b)1 does not list it for alterations.
Explore Furnaces
- Furnace or Air Handler in the Garage: Title 24 Rules for a Swap
- Furnace Replacement Title 24 Checklist
- Wall Furnace or Floor Furnace Replacement: What Title 24 Says
- What Furnace Efficiency (AFUE) Does California Require?
View all Furnaces guides → · HVAC and Water Heating · Title 24 guide