Title 24 & HERS Glossary
Every acronym on this site, defined in one place — Title 24, HERS, ECC, the CF certificates, QII, climate zones, and the terms that changed in the 2025 Energy Code.
Title 24
California's Building Energy Efficiency Standards — Title 24, Part 6 of the California Code of Regulations. It sets the minimum energy-performance rules for new construction, additions, and alterations statewide, and the California Energy Commission updates it on a three-year cycle. The 2025 edition took effect January 1, 2026.
Title 24, Part 6
The specific part of California's Title 24 that contains the Building Energy Efficiency Standards. "Title 24" in the energy-compliance context almost always means Part 6.
HERS
Home Energy Rating System — California's program of independent field verification confirming that energy measures (ducts, HVAC, insulation, envelope) were actually installed to Title 24 standards. A HERS test is performed by a certified third-party rater, never the installing contractor.
ECC
Energy Code Compliance — the California Energy Commission's current name for the HERS rater program. As of the 2025 Energy Code, HERS raters are ECC raters; the tests, forms, and registries are unchanged.
CF1R
Certificate of Compliance (Residential) — the energy report filed at permit application showing the project's design meets Title 24. Prepared by a designer or energy consultant, usually before construction starts.
CF2R
Certificate of Installation (Residential) — completed by the installing contractor to certify that the energy measures were installed as designed. It must be registered before the rater files the verification.
CF3R
Certificate of Verification (Residential) — signed by the HERS / ECC rater after field testing confirms the installed work passes. It is registered with a CEC-approved registry and is what the building inspector checks at final.
NRCC
Nonresidential Certificate of Compliance — the Title 24 compliance document for commercial and nonresidential projects, the nonresidential counterpart to the CF1R.
NRCA
Nonresidential Certificate of Acceptance — documents the acceptance testing (lighting controls, mechanical systems) required to close a nonresidential energy permit.
NRCV
Nonresidential Certificate of Verification — the nonresidential field-verification certificate, signed by a rater where third-party verification is required.
Title 20
California's Appliance Efficiency Regulations (Title 20 of the California Code of Regulations). Distinct from Title 24: Title 20 governs the efficiency of appliances and equipment sold in California, while Title 24 governs how buildings use energy.
QII
Quality Insulation Installation — a Title 24 verification, defined in Reference Appendix RA3.5, in which a certified HERS rater inspects insulation and the air barrier before drywall. It is a prescriptive requirement for most new low-rise residential construction and additions over 700 square feet.
CHEERS
California Home Energy Efficiency Rating Services — a CEC-approved data registry and ECC provider where compliance documents (including the CF3R) are registered. ERE registers all of its field verifications with CHEERS.
AHJ
Authority Having Jurisdiction — the city or county building department that issues the permit and performs the final inspection. Each AHJ runs its own permit portal and inspection process.
Climate zone
One of California's 16 building climate zones, assigned by project address. The climate zone determines which Title 24 measures and HERS tests a project requires.
Duct leakage test
A HERS test that pressurizes the duct system to measure how much conditioned air leaks out. Required on most permitted HVAC changeouts and duct replacements; excessive leakage is the most common reason a test fails.
Blower door test
A test that depressurizes the whole building envelope with a calibrated fan to measure total air leakage. Used to verify envelope tightness on new construction and some alterations.
Refrigerant charge verification
A HERS test confirming an air conditioner or heat pump has the correct refrigerant charge for efficient operation. Under the 2025 code it is required for heat pumps in all 16 climate zones.
Fan watt draw
A HERS measurement of the electrical power an air handler's fan draws relative to airflow (fan efficacy), confirming the system moves air efficiently enough to meet Title 24.
HPWH
Heat Pump Water Heater — a water heater that moves heat instead of generating it directly. Under the 2025 Energy Code it is effectively the prescriptive baseline for residential water heating, and installs trigger readiness items like a dedicated 30-amp circuit.
LSC
Long-term System Cost — the compliance metric introduced in the 2025 Energy Code, replacing Time Dependent Valuation (TDV) as the basis for the performance compliance budget.
TDV
Time Dependent Valuation — the energy-cost metric used in the 2022 and earlier codes to value energy by time of use. Replaced by Long-term System Cost (LSC) in the 2025 code.
ADU
Accessory Dwelling Unit — a secondary residence on a single-family lot. New ADUs generally require a CF1R energy report and trigger HERS measures; conversions of existing space have lighter requirements than new builds.
MERV
Minimum Efficiency Reporting Value — the rating of an air filter's ability to capture particles. Title 24 ventilation requirements specify minimum filter MERV ratings for residential systems.
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