What Is the Title 24 Energy Budget? LSC, Source Energy and the Old TDV
The energy budget is the most energy a proposed building may use, calculated by approved software from a standard design. For new buildings it is counted in two units, long-term system cost (LSC) and source energy; for additions and alterations, in LSC alone. TDV was the earlier unit for LSC, and neither unit is a utility bill.
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Why the budget is counted by the hour
Section 100.2 says LSC is calculated by multiplying the site energy used in every hour of the year by a published LSC hourly factor. Those factors vary by hour, by energy type (electricity, natural gas or propane), by climate zone and by building type, and they are summarized in Joint Appendix JA3. The same kilowatt-hours therefore count differently at different hours, and gas is weighted on its own scale rather than converted to kWh. See the joint appendices guide for where JA3 sits.
The second unit, source energy
Source energy is a separate tally. The same hourly site use is multiplied by Btu factors reflecting the fossil fuel burned on site or caused to be burned to meet the building's electric demand, using the long-term marginal hourly resources the Commission projects. A new building has to satisfy both currencies, and the manual compares them separately.
Where TDV went
The 2025 single-family performance budget uses LSC instead of time dependent valuation (TDV) energy. Older articles, some consultant pages and even a few passages in the compliance manual still say TDV, so treat TDV as the older label, not a separate 2025 requirement.
What sits inside LSC
- Efficiency LSC covers space conditioning, water heating, mechanical ventilation and the self-utilization credit.
- Total LSC adds the PV system, battery storage, lighting, demand flexibility and other plug loads.
The consequence for solar is on why solar cannot fix a failing efficiency result.
What the number is for
It decides pass or fail and sets the margin, covered in what compliance margin means. LSC is the Commission's projected present value of costs to California's energy system over 30 years and does not predict individual utility bills. The rules behind the calculation live in the ACM reference manual guide, and the method comparison is on prescriptive versus performance. Orders start on the residential report page.
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
The single-family performance budget now uses LSC instead of TDV. The word survives in older documents and in a few places in the compliance manual.
No. It is a projected 30-year present value of costs to the state energy system, and the code says it does not predict individual bills.
Explore Performance Calculations
- Which Title 24 Performance Credits Need an ECC-Rater Test?
- Why Did My Project Fail Title 24? How to Read a Failing Result
- Efficiency LSC vs Total LSC: Why Solar Cannot Fix a Failing Efficiency Result
- Existing + Addition + Alteration: How the Performance Method Works
- Prescriptive vs Performance Compliance for Home Additions
View all Performance Calculations guides → · Reports and Calculations · Title 24 guide