Why Do Two Title 24 Consultants Get Different Results for the Same House?
Both can be right. Approved programs share one simulation engine and generate the reference house automatically, so a gap comes from inputs and choices: the plan version, assumed equipment, existing-condition settings, claimed credits or software date. Compare those, not the final margin.
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Same engine, different inputs
Every approved program uses the California simulation engine and the same report generator as the state's public-domain program. Since the reference house is generated automatically from your inputs, the arithmetic is not where reports drift apart. The inputs are.
The six usual causes
- Different plan revisions. Inputs must match the final approved plan set, so a report built on an older sheet disagrees with one built on the current sheet.
- Different treatment of existing parts. An existing component entered as verified by an ECC-Rater, or as an assumed level, changes the reference.
- Different equipment assumptions, such as the heat pump rating or water heater type.
- Different credits claimed. Anything above the minimum, such as a higher SEER2 or quality insulation installation, appears only if the consultant modeled it.
- Different compliance paths, prescriptive on one report and performance on the other.
- Different software dates.
Software dates matter
When a program is updated, the previous version expires 90 days after the new one is approved for a major change and 60 days for a minor one, and the modeling rules are revised no more than twice a year, in January and July.
How to reconcile them
Ask each consultant for the summary page and the electronic input file. A building department can require the input file for a performance certificate, and it is the cleanest way to compare two runs line by line. Look at the special features list and the verification list on each: a credit that needs field testing brings an ECC-Rater visit that a plainer report avoids. The difference is harmless if both pass with the same plans. It is an error if one used the wrong window area or a piece of equipment you are not installing.
Where to read more
The reference manual guide explains why approved programs agree, and compliance software covers approval. If the plan checker questions your report, see why the checker says it does not match. Choosing a preparer is covered in how to choose a consultant, and every residential report we prepare is built from the plans you send.
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
No. Check the plan revision, the equipment listed and whether any credit needs a field test you did not plan for.
Either, if it matches the plans submitted. The department decides what it accepts.
Explore Energy Calculations
- The Title 24 ACM Reference Manual, Explained
- Does a Title 24 Calculation Require a Site Visit?
- Front Orientation on a Title 24 Report: Why It Matters and What Rotating the House Does
- How Does a Heat Pump Change a Title 24 Calculation?
- How Do Duct Location and Leakage Affect Title 24 Calculations?
View all Energy Calculations guides → · Reports and Calculations · Title 24 guide