California Title 24 Energy Compliance Calculator
Estimate whether your residential building meets California Title 24 Part 6 energy efficiency standards by comparing your proposed design energy use against the standard (baseline) design budget.
Formulas Used
Annual Heating Load (BTU/yr):
Qheat = (Uwall·Awall + Uroof·Aroof + Uwin·Awin) × HDD65 × 24
Qinf,heat = (ACH50 ÷ 20) × Volume × 0.018 × HDD65 × 24
Eheat = (Qheat + Qinf,heat) ÷ HVACeff
Annual Cooling Load (BTU/yr):
Qcool,cond = (Uwall·Awall + Uroof·Aroof + Uwin·Awin) × CDD65 × 24
Qsolar = SHGC × Awin × 200 × (CDD ÷ 1000) × 1000
Qlighting = LPD × CFA × 3.412 × 2000
Ecool = (Qcool,cond + Qsolar + Qinf,cool + Qlighting) ÷ COPcooling
Compliance Margin:
Margin = Estandard,total − Eproposed,total (positive = compliant)
Energy Use Intensity:
EUI = Etotal (kBTU/yr) ÷ CFA (ft²)
Assumptions & References
- Based on California Title 24, Part 6 (2022 Building Energy Efficiency Standards), effective January 1, 2023.
- Standard (baseline) U-factors from Table 150.1-A (prescriptive envelope requirements by climate zone).
- Heating and cooling degree days (HDD65/CDD65) sourced from CEC Climate Zone Reference Data.
- Wall area estimated as 1.5 × CFA; roof area as 0.55 × CFA; ceiling height assumed 9 ft.
- Natural infiltration rate approximated as ACH50 ÷ 20 (Sherman-Grimsrud simplified method).
- Air heat capacity: 0.018 BTU/(ft³·°F).
- Cooling COP assumed 3.5 (≈ SEER 12) for both proposed and standard designs.
- Standard lighting power density: 0.60 W/ft² per Title 24 Table 150.0-A.
- Standard infiltration baseline: 7.0 ACH50 (pre-2022 typical construction).
- Lighting internal gains calculated at 2,000 occupied hours/year; 1 W = 3.412 BTU/hr.
- This calculator provides a simplified performance estimate. Official compliance requires CEC-approved software (e.g., EnergyPro, CBECC-Res).
- Reference: CEC Building Energy Efficiency Standards