California is a Title 24 state, not an IECC state - REScheck is not a recognized compliance path here, full stop. What California does require, by statute, is a documented load calculation for new construction, additions, and HVAC changeouts alike. Every claim on this page is checked against the California Energy Commission's own code text and compliance manuals - see the Verification Appendix.
Last verified September 5, 2026 against the sources linked above. Change log
Most of the state pages on this site are about which edition of the International Energy Conservation Code (IECC) a state or city has adopted. California isn't on that spectrum at all. It runs its own energy code - the Building Energy Efficiency Standards, published as Title 24, Part 6 of the California Code of Regulations - and has run its own code, independent of the IECC, for decades. The U.S. Department of Energy's own state profile for California confirms this structurally: Current State Code (both Commercial and Residential) is listed as the "2025 Building Energy Efficiency Standards," adopted December 17, 2024 and effective January 1, 2026, with State Amendments marked "No" - meaning this isn't an amended IECC edition, it's California's own document from the ground up.1
Enforcement runs through the same local building department structure as any other state - your city or county reviews the permit and inspects the work - but the document they're checking against is Title 24, Part 6, not a version of the IECC. The California Energy Commission (CEC) is the state agency that writes and updates the code itself; local plan reviewers apply it.
California doesn't use the IECC's national climate-zone map. The state has its own system of 16 building climate zones, assigned by ZIP code, developed by the CEC specifically to capture California's unusually wide range of coastal, valley, desert, and mountain conditions within a single state.2 If you've seen a national climate-zone designation like "3B" or "4A" attached to a California city elsewhere on this site or on a competitor's page, that's the IECC's numbering, not California's - the two systems don't map onto each other one-to-one, and Title 24 compliance software wants the CEC's own zone number, not the IECC's. Confirm your project's CEC climate zone (by ZIP code) before assuming a number from anywhere else applies.
We do not offer a REScheck report for California projects, and we don't build one to look like it satisfies Title 24 - it wouldn't. What we prepare is the Manual J load calculation: the room-by-room heating and cooling load numbers a system needs to be sized against. That calculation is a genuine, separately useful input into a California project regardless of which state energy code applies, because equipment sizing is an engineering question, not a code-edition question. Section 2 explains exactly where that fits, and where it doesn't, inside Title 24's own structure.
It's worth being direct about this rather than hedging it, because a lot of national "does REScheck work in my state" content gets California wrong or glosses over it. REScheck is a U.S. Department of Energy tool built to document one specific IECC compliance path: the total-UA envelope trade-off under IECC Section R402.1.5. California's Title 24, Part 6 was never built on the IECC's chapter structure, so there is no equivalent section for REScheck to document. DOE's own state adoption page reflects that gap directly - where most states get a plain "Yes" or "Applicable by County or Jurisdiction" answer in the "Can use COM/REScheck" field, California's field is simply left blank.1
Title 24, Part 6 compliance runs on its own family of state-specific certificates, generally referred to by their form-number prefixes:
Preparing and registering that CF1R/CF2R/CF3R package is a separate, state-regulated process from what we do. It generally requires either a licensed design professional taking responsibility for the compliance documentation, or - for alterations that trigger field verification - registration through a HERS Provider or ECC-Rater data registry.4 We do not prepare or register Title 24 energy compliance certificates. If your project needs one, that filing runs through your architect, energy consultant, or HERS/ECC-Rater, separate from the report you'd order here.
Equipment sizing is where the two threads meet. Title 24's own energy code requires a documented load calculation as an input to the CF1R itself - Section 150.0(h) covers heating and cooling load calculations and minimum/maximum equipment capacity, and it applies whether the CF1R being filed is for new construction, an addition, or a qualifying alteration.5 The load-calculation methodologies Title 24 accepts are the same industry-standard ones used nationally: ACCA Manual J, the ASHRAE Handbook (Fundamentals, Equipment, and Applications volumes), or the SMACNA Residential Comfort System Installation Standards Manual, with fixed indoor design temperatures of 68°F for heating and 75°F for cooling, and outdoor design conditions drawn from the Energy Code's own Reference Joint Appendix JA2 or from ACCA Manual J itself.6 Equipment selection is then made per ACCA Manual S, matched against those loads.
That Manual J is a genuinely useful, standalone deliverable for a California project - your HVAC contractor needs it to select and quote equipment correctly, and whoever prepares your CF1R needs it as an input regardless of who does that filing. It is not, on its own, the CF1R itself, and we don't represent it as one.
This is the section that trips people up on existing-home projects specifically, so it's worth stating plainly: California's Energy Code does not limit its load-calculation requirement to new construction. The California Energy Commission's own compliance guidance is explicit that documented sizing is required across all three project types:
"The Energy Code requires documented sizing for almost all equipment installations: New Construction: All residential and non-residential builds. Additions: Any project adding a new dedicated HVAC unit to a space... Alterations: Equipment replacements (change-outs) in existing buildings."6
The mechanism behind this is the Energy Code's own definition of an "alteration," which is deliberately broader than most people expect. The CEC's compliance manual draws a specific line: a repair - fixing or maintaining a component so it continues to work - is outside the Energy Code's scope. But "replacement of any component, system, or equipment for which there are requirements in the Energy Code is considered an alteration and not a repair."7 A failed condenser that gets fixed is a repair. A failed condenser that gets replaced is an alteration - and alterations are squarely inside the Energy Code's scope, including its sizing requirements.
Specifically, when a changeout replaces the entire space-conditioning system - "the air handler and all the system heating/cooling equipment (e.g., outdoor condensing unit and indoor cooling or heating coil for split systems; or complete replacement of a package unit)" plus an entirely new duct system - the Energy Code treats it as meeting all applicable mandatory and prescriptive new-construction-level requirements, explicitly including Section 150.0(h)1-2, cooling and heating load calculations.8 That's the enforcement hook: a full system swap doesn't get to skip the load calculation just because the house already exists.
Partial component replacements - say, a condenser coil matched to an existing furnace, without touching the whole system - fall under a different alteration path (airflow verification, refrigerant charge confirmation, and thermostat requirements under Section 150.2(b)1F) rather than automatically triggering a fresh Section 150.0(h) load calculation. Which bucket a given changeout lands in depends on exactly which components are being replaced, which is worth confirming with your plan reviewer or HERS Rater before assuming either way.
For additions specifically, if the addition reuses the home's existing HVAC system rather than adding a new dedicated unit, the requirement shifts: the project must document that the existing system meets certain minimum criteria, and block-load calculations (the whole addition treated as one combined load, rather than room-by-room) are permitted for that purpose.5 Where a new, dedicated HVAC unit is being added for the addition, the same Section 150.0(h) load-calculation and sizing rules that apply to new construction apply there too, and the CEC's HVAC guidance separately confirms that maximum equipment-capacity limits (Table 150.2-A for heating, Table 150.2-B for cooling) kick in whenever airflow for that new system isn't field-verified at 350 CFM per ton or higher.9
The CF1R/CF2R/CF3R filing and the Manual J are two different things - keep them that way. A permit checklist that asks for "energy compliance documentation" in California is asking for the CF1R package, not a Manual J by itself. If your plan reviewer, HVAC contractor, or HERS Rater asks specifically for equipment-sizing documentation to complete their own CF1R filing, that's exactly what we prepare. If the checklist is asking you to produce the full CF1R/CF2R/CF3R set yourself, that's outside what we do, and we'll tell you so up front rather than let a mismatch surface at plan review.
16 CEC climate zones, assigned by ZIP code, are not the same as the national IECC zone map. Since the 2013 Standards cycle, every California ZIP code sits entirely inside one of the CEC's 16 zones, but a handful of larger cities and metro areas straddle more than one zone across their ZIP-code range - the Los Angeles basin and San Diego County are the most commonly cited examples. Confirm your project's specific CEC climate zone by ZIP code, ideally through the Energy Commission's own zone-lookup resources, rather than assuming from the city name.2
A full system swap is treated like new construction for sizing purposes; a partial swap generally isn't. If your HVAC contractor is replacing the whole system (air handler, outdoor unit, coil, and ducts), expect the same load-calculation and sizing scrutiny a new house would get. If only one refrigerant-containing component is being replaced against an otherwise-existing system, the applicable alteration path is different (and often lighter), centered on airflow and refrigerant-charge verification rather than a fresh Manual J. Tell us which scenario applies to your project so we scope the right deliverable.
ADUs split by type. A detached accessory dwelling unit is generally treated by the Energy Code as a newly constructed building for compliance purposes, while an attached ADU or a garage conversion is typically treated as an addition or alteration to the existing residence under Section 150.2(a).5 Either way, the equipment serving the ADU still needs its own sizing documentation and, per current Mechanical Code practice, its own thermostat and dedicated system rather than shared return air with the main house.
We are not a HERS Rater or ECC-Rater, and we don't register documents with a HERS or ECC-Rater data provider. Where your project's alteration path requires field verification and CF3R registration, that step happens through a separately credentialed rater, independent of the Manual J load calculation we provide.
What to confirm with your local building department or energy consultant before ordering:
Does California use the IECC, and will REScheck work for a California permit? No to both. California runs its own Title 24, Part 6 energy code with its own certificate family (CF1R, CF2R, CF3R), and DOE's own state profile leaves the "Can use COM/REScheck" field blank for California rather than marking it Yes.1 REScheck's UA method is built for the IECC's structure and has no equivalent inside Title 24.
Is a load calculation required for an HVAC changeout in California, not just new construction? Yes, in most cases. The Energy Code treats an equipment changeout as an alteration, and the CEC's own compliance manual lists "Alterations: Equipment replacements (change-outs)" alongside new construction and additions as project types that require documented sizing.6 A full system swap is held to the same Section 150.0(h) load-calculation requirement as a new house.
If REScheck doesn't apply here, what does a Manual J actually do for a California project? It documents the heating and cooling loads your system needs to be sized against - the engineering question every state asks, routed through Title 24's own Section 150.0(h) instead of the IECC. Your HVAC contractor and whoever files your CF1R both need those numbers.
Do you prepare California's Title 24 energy compliance paperwork - CF1R, CF2R, or a HERS rating? No. That filing runs through a licensed energy consultant or a HERS/ECC-Rater registered with an approved data registry - a separate, state-regulated process from the Manual J load calculation we prepare.
Who prepares my Manual J report? Travis Smith, The Plans Examiner. He holds the same certification your building department's plan reviewer holds; the specifics are at the end of this page.
My building department is asking for something and I'm not sure if it's a load calc or a full Title 24 filing - what do I do? Send us what your checklist or plan reviewer actually says, plus your jobsite ZIP code, and we'll tell you plainly whether a Manual J covers it or whether you also need a separate CF1R filing elsewhere.
Need a Manual J load calculation for a California project? Whether it's new construction, an addition, or a full HVAC changeout that Title 24 treats as an alteration, we prepare a room-by-room ACCA Manual J load calculation from your plans, sized to California's fixed 68°F heating / 75°F cooling design conditions and your project's CEC climate zone. A Manual J report is $249 for homes up to 3,000 sq ft, $349 for 3,001 to 4,500 sq ft, and $449 for 4,501 to 6,000 sq ft. Larger homes or projects with three or more systems are quoted from your plans. Manual S equipment selection is available as an add-on; see the Manual J page for the full pricing ladder.
We do not offer REScheck or a Title 24 CF1R filing for California projects. Those are a separate compliance regime handled by a licensed energy consultant or HERS/ECC-Rater. If you already have someone handling that filing and just need the load-calculation input, that's exactly what we provide.
Every Manual J report we prepare comes with the same guarantee: accepted by your building department, or we revise it free until it clears.
Building an ADU? See our Manual J for ADU guide for what the calculation needs to cover on a detached versus attached unit. Replacing a heat pump or furnace? See our guide on changeout sizing requirements for how the "repair vs. alteration" line plays out in practice.
Contact us with your plans, your jobsite address, and whether your project is new construction, an addition, or a changeout, and we'll confirm exactly what your Manual J needs to cover.
Every claim on this page was checked directly against the California Energy Commission's own published code text, compliance manuals, and forms, or against DOE's own state adoption page, during this research pass - not a national aggregator or a secondary blog summary, except where explicitly noted below.
California's current code = 2025 Building Energy Efficiency Standards, effective 01/01/2026, adopted 12/17/2024, no state amendments, "Can use COM/REScheck" left blank. VERIFIED (primary source). energycodes.gov/status/states/california's own State Profile table states this directly.1
16 CEC building climate zones, assigned by ZIP code. VERIFIED (primary source). The California Energy Commission's own "Climate Zone tool, maps, and information" page describes the 16-zone system and its ZIP-code-based assignment method directly.2
CF1R/CF2R/CF3R certificate structure and form names. VERIFIED (primary source). Pulled directly from CEC's own posted CF1R-ALT-02-E and CF2R-ALT-05-E form-instruction PDFs (energy.ca.gov/filebrowser), which name and describe the Certificate of Compliance, Certificate of Installation, and Certificate of Verification roles, and confirm HERS/ECC-Rater data-registry registration for alterations requiring field verification.34
Section 150.0(h) load-calculation and sizing requirement; approved methodologies (Manual J, ASHRAE Handbook, SMACNA); fixed design temperatures 68°F/75°F. VERIFIED, primary + corroborating secondary. The CEC's own 2025 Single-Family HVAC FAQ page and 2022 Compliance Manual Chapter 9 confirm the Section 150.0(h) sizing and load-calculation requirements directly.9 The specific list of approved methodologies and the 68°F/75°F fixed design temperatures were corroborated against Efficiency First California's summary of the 2025 Energy Code's HVAC requirements, a trade-association secondary source whose factual claims matched the CEC's own compliance manual and FAQ page on every point checked.10
Repair vs. alteration definition; documented sizing required for new construction, additions, and changeouts alike. VERIFIED (primary source). Quoted directly from CEC's 2022 Single Family Residential Compliance Manual, Chapter 9 ("Additions, Alterations, and Repairs").67
Entirely new or complete replacement space-conditioning system triggers Section 150.0(h)1-2 load calculations as part of an alteration. VERIFIED (primary source). Confirmed against the 2025 California Energy Code, Title 24 Part 6, Section 150.2, Subchapter 9, on codes.iccsafe.org, and cross-checked against CEC's own Chapter 9 compliance-manual language describing the same trigger.8
Block-load exception for additions reusing an existing HVAC system; Table 150.2-A/B maximum capacity limits tied to field-verified airflow. VERIFIED (primary source). Confirmed directly against CEC's 2025 Single-Family HVAC FAQ page.9
ADU treatment: detached ADUs as newly constructed, attached ADUs/conversions as additions under 150.2(a). VERIFIED, secondary corroboration. Sourced from CEC's own Chapter 9 compliance-manual ADU example language; a full county-by-county or ADU-type-by-type confirmation was not independently re-pulled for every scenario during this pass.
What remains genuinely unconfirmed: the exact CEC climate zone for any specific address not looked up directly through the Commission's own tools; whether a given local jurisdiction layers additional local amendments on top of the statewide Title 24 baseline (some California cities do adopt reach codes beyond the state minimum, and those were not surveyed here); and the precise alteration-path classification for component combinations not explicitly named in the sources above. Confirm any of these with your local building department, HERS Rater, or energy consultant before finalizing a compliance strategy.
This page summarizes California's statewide Title 24, Part 6 energy code and its load-calculation requirements for general guidance. Local jurisdictions may layer additional reach-code requirements on top of the state minimum. Always confirm current requirements with your local building department, energy consultant, or HERS Rater before finalizing design or bidding.
VERIFIED (primary source): U.S. Department of Energy, Building Energy Codes Program, "California | State Profile," energycodes.gov/status/states/california. ↩↩↩↩
VERIFIED (primary source): California Energy Commission, "Climate Zone tool, maps, and information supporting the California Energy Code," energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/climate-zone-tool-maps-and. ↩↩↩
VERIFIED (primary source): California Energy Commission, "2022 CF1R-ALT-02-E Prescriptive Alterations HVAC" form instructions, energy.ca.gov/filebrowser/download/4688; "2022-CF1R ALT-05-E Prescriptive Alterations," energy.ca.gov/filebrowser/download/5003. ↩↩
VERIFIED (primary source): California Energy Commission, "2025 CF2R-ALT-05-E Prescriptive Alterations - That Do Not Require ECC Field Verification," energy.ca.gov/filebrowser/download/8305?fid=8305, confirming CF1R-ALT-02/HERS or ECC-Provider data-registry registration for alterations requiring field verification. ↩↩
VERIFIED (primary source): California Energy Commission, "2019 Chapter 9 - Additions, Alterations, and Repairs," 2022 Single Family Residential Compliance Manual, energy.ca.gov/sites/default/files/2021-03/2019_Chapter%209%20-%20Additions%20Alterations%20Repairs_ADA.pdf, and full Chapter 9 PDF at energy.ca.gov/filebrowser/download/5131. ↩↩↩
VERIFIED, primary + corroborating secondary: California Energy Commission, 2022 Single Family Residential Compliance Manual, Chapter 9 (energy.ca.gov/filebrowser/download/5131), and 2025 Single-Family HVAC FAQ (energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/energy-code-support-center/hvac-0), corroborated by Efficiency First California, "The 2025 Title 24 Roadmap: Navigating HVAC Load Calculation Requirements," efficiencyfirstca.org/advocacy/the-2025-title-24-roadmap-navigating-hvac-load-calculation-requirements/. ↩↩↩↩
VERIFIED (primary source): California Energy Commission, 2022 Single Family Residential Compliance Manual, Chapter 9, repair-vs.-alteration definition quoted directly, energy.ca.gov/filebrowser/download/5131. ↩
VERIFIED (primary source): 2025 California Energy Code, Title 24 Part 6, Subchapter 9, Section 150.2, codes.iccsafe.org/content/CAEC2025P1/subchapter-9-single-family-residential-buildings-additions-and-alterations-to-existing-residential-buildings, listing Section 150.0(h)1-2 among the requirements triggered by an entirely new or complete replacement space-conditioning system installed as part of an alteration. ↩
VERIFIED (primary source): California Energy Commission, "2025 Single-Family Heating, Ventilation, and Air Conditioning (HVAC) FAQ," energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/energy-code-support-center/hvac-0. ↩↩↩
Efficiency First California, "The 2025 Title 24 Roadmap: Navigating HVAC Load Calculation Requirements," efficiencyfirstca.org/advocacy/the-2025-title-24-roadmap-navigating-hvac-load-calculation-requirements/ - a trade-association secondary source, cross-checked against the primary CEC sources above and found consistent on every factual point used on this page. ↩
Travis Smith, ICC-Certified Residential Plans Examiner. The same certification your building department's plan reviewer holds - working for you.