California's Title 24 energy code is unusual among state energy codes in one important respect: parts of it aren't just a paperwork exercise completed before construction begins. Certain compliance measures have to be physically verified in the field, after installation, by a certified HERS rater — and if that verification doesn't happen, or doesn't pass, the project can't get final approval regardless of how the original compliance documentation looked.
HERS stands for Home Energy Rating System, and in the California Title 24 context, HERS raters are independent, certified third parties who inspect and test specific measures claimed in a project's compliance calculation to confirm they were actually installed and performing as modeled — not just specified on paper. This creates a field verification layer on top of the compliance documentation itself, closing the gap between "what was designed to be built" and "what actually got built."
Energy code compliance documentation (whether prescriptive or performance-based) is prepared based on what's specified in construction documents — but specifications don't guarantee installation quality. A duct system specified to have low leakage can still end up leaky if installed carelessly; insulation specified at a certain R-value can be installed with gaps and compression that meaningfully reduce its actual performance. HERS verification exists specifically to catch this gap between design intent and field execution for the measures where installation quality has the biggest impact on actual energy performance.
While the specific list depends on the compliance path and measures claimed for a given project, commonly verified items include:
Not every measure requires HERS verification on every project — it depends on which compliance path and specific credits or requirements were used in the original Title 24 submission.
Because HERS verification happens after installation (some measures, like duct leakage testing, need to occur before drywall closes up access to the ductwork; others happen closer to final inspection), it needs to be built into the construction schedule as a required step, not treated as an afterthought squeezed in right before closing. Missing the correct window for a particular test — for example, needing duct access that's since been covered — can create real rework and delay.
If a verified measure doesn't pass — duct leakage tests higher than the compliance calculation assumed, for instance — the project generally has two paths forward: correct the installation issue and re-test, or revise the compliance calculation to reflect the actual as-built performance (which may require offsetting improvements elsewhere to still meet the overall energy budget). Either way, it becomes a real project delay, which is exactly why getting installation quality right the first time — rather than treating specified performance as automatically achieved — matters so much under Title 24's verification framework.
For HVAC contractors, several of the most commonly verified measures — duct leakage, refrigerant charge, airflow — fall directly within mechanical scope of work. This means HVAC installation quality on a Title 24 project isn't just about customer satisfaction and system performance; it's directly tied to whether the project can pass its required code verification and receive final approval at all.
A duct system correctly designed under Manual D and properly installed to that design is far more likely to pass duct leakage verification without rework than a system where duct sizing and layout were approximated. Similarly, correct equipment sizing under Manual J and Manual S reduces the likelihood of airflow or performance issues surfacing during HERS verification. The upstream design quality directly affects downstream verification outcomes.
Who performs HERS verification — the contractor or an independent party?
An independent, certified HERS rater performs the verification testing — it's not something the installing contractor self-certifies.
Does every Title 24 project require HERS verification?
Not necessarily every measure on every project — it depends on which compliance path and specific credits or requirements were used in the compliance calculation. Projects claiming certain performance credits are more likely to trigger corresponding verification requirements.
When during construction does HERS verification typically happen?
It varies by measure — duct leakage testing often needs to happen before areas are closed up (e.g., before drywall), while other verifications may occur closer to final inspection. Planning verification timing into the construction schedule is essential.
What happens if a verification test fails?
The installation issue typically needs to be corrected and re-tested, or the compliance calculation revised to reflect actual as-built performance — either path adds time and cost, reinforcing the value of getting installation right the first time.
Psychro.Pro helps ensure Manual J-based equipment sizing and Manual D duct design translate into installations that hold up under Title 24 HERS verification. Learn more.
