9.2 HERS Verification & Duct Testing Requirements

What a HERS Rater Does

HERS stands for Home Energy Rating System, a diagnostic testing and rating framework that originated nationally through the Residential Energy Services Network (RESNET) and was adopted into California's Title 24 enforcement structure as the mechanism for confirming, in the field, that certain mandatory and prescriptive energy measures were actually built the way the paperwork claims. A HERS rater is an individual who has completed CEC-approved (and typically RESNET-accredited) training and certification to perform these tests. Note that in recent CEC communications the terminology has begun shifting toward "Energy Code Compliance (ECC)" branding for providers and raters; the underlying CF-form numbering and testing requirements discussed in this section continue regardless of which label a given jurisdiction or provider currently uses, so C-20 candidates should recognize both terms.

The defining feature of a HERS/ECC rater is independence: the rater must be a disinterested third party with no financial relationship to the installing contractor, which preserves the integrity of the verification. A rater is not part of the contractor's crew, does not report to the contractor, and is not paid contingent on the installation passing. In practice, the rater is typically engaged (and paid) by the contractor or builder as a required part of the project, but their certification and test results are filed independently into a state-recognized registry maintained by an approved HERS/ECC Provider organization.

On a jobsite, a HERS rater's core responsibilities include:

• Duct leakage testing -- pressurizing the duct system with a calibrated fan and measuring the CFM25 leakage rate against the applicable threshold.
• Refrigerant charge verification -- confirming the system was charged correctly (commonly via the superheat or subcooling method referenced against manufacturer specifications), now mandatory statewide for heat pumps under the 2025 cycle.
• Airflow and fan watt draw testing -- confirming the system delivers its rated airflow and that fan energy consumption meets the applicable limit, mandatory on new HVAC systems under the 2025 cycle.
• Registering results and issuing the CF3R -- the Certificate of Field Verification and Diagnostic Testing (fully covered in Section 9.4), which the local building department relies on before finaling the permit.

When HERS Verification Is Triggered

HERS/ECC verification is not limited to brand-new homes. C-20 contractors encounter it across several common scenarios:

1. New construction -- any system subject to the mandatory or prescriptive measures of the applicable Energy Code cycle requires field verification as a matter of course.
2. Duct replacement or extension -- testing is generally triggered once more than 40 linear feet of existing ductwork is replaced. Whether the tighter new-construction threshold or a looser alteration threshold applies depends on how much of the system is new material (see the table below).
3. Equipment change-outs -- most full replacements of a furnace, air conditioner, or heat pump trigger HERS verification of refrigerant charge and, where ductwork is involved, duct leakage, filed under the applicable alteration compliance forms (commonly labeled with an "-ALT" suffix, such as CF1R-ALT).
4. Substantial duct sealing work -- projects whose scope is specifically to seal and improve an existing duct system are verified to confirm the improvement was actually achieved, not merely claimed.

Duct Leakage Thresholds

Duct leakage testing measures air escaping the duct system in CFM25 -- cubic feet per minute of leakage recorded while a calibrated duct blaster fan pressurizes the system to a standardized 25 pascals test pressure. This standardized pressure allows results from different jobs, raters, and equipment to be compared consistently under the RESNET testing protocol that California's field verification procedures reference.

The allowable leakage percentage is not a single flat number -- it scales with how much of the duct system is new versus existing:

Because duct leakage percentages have tightened across recent code cycles (the prior 2019/2022 cycle used a 6% new-construction threshold before the 2025 cycle reduced it to 5%), a contractor should always confirm the exact figure against the code cycle governing the permit in hand rather than relying on a number learned on a previous job -- the applicable cycle depends on the permit application date discussed in Section 9.1.

What Happens When a System Fails Testing

If a HERS/ECC rater's test results exceed the applicable threshold, or refrigerant charge is out of range, the system does not pass. The contractor must correct the deficiency -- commonly by sealing additional duct joints with mastic or by adjusting refrigerant charge to the manufacturer's specification -- and the rater must retest before a passing CF3R can be filed. Because a retest typically means scheduling a second rater visit at additional cost and delay, experienced C-20 contractors build a margin of safety into their own duct sealing and charging practices rather than aiming to just barely clear the threshold, treating the HERS test as a checkpoint to pass comfortably rather than a target to meet exactly.