Does a ductless mini-split in an ADU still need ECC field verification?

Yes, in most cases. Going ductless removes the duct tests, but the CEC's 2025 ADU FAQ says mini-split and multi-split systems may still need ECC-Rater field verification and diagnostic testing, depending on project scope. For a heat pump, that usually includes refrigerant charge verification, which Table 150.1-A requires for heat pumps in all climate zones.

Tests the CEC lists for mini-splits and multi-splits

• Refrigerant charge in all climate zones, per Section 150.1(c)7A. The code names mini-split systems explicitly. If a system can't be checked with the standard procedure, the installer weighs in the charge and an ECC-Rater confirms it.
• Minimum airflow, where the verification procedure calls for it.
• Verified SEER2, HSPF2 and rated heating capacity, typically when the performance model takes credit for them.
• Duct leakage and fan efficacy, only for ducted systems. A truly ductless system skips these.

The CEC points to Reference Appendix Table RA2-1 for the full list. The tests that apply to your project are listed on your CF1R.

Other ECC items in a mini-split ADU

The HVAC system isn't the only thing an ECC-Rater checks. In its ADU training, the CEC says ECC verification of the whole-dwelling ventilation (IAQ) fan is required 100 percent of the time, and a vented kitchen range hood installed to meet the indoor air quality rules must also be verified. Insulation (QII) and other items are added when they're required or modeled for credit.

Additions are verified too

An attached ADU or garage conversion is an addition, and the CEC says additions require ECC verification 100 percent of the time. Prescriptive refrigerant charge verification for heat pumps in additions applies in all climate zones.

How the process works

ECC (Energy Code Compliance) verification replaced HERS field verification on January 1, 2026. The steps are the same as before:

1. The CF1R lists every measure that needs field verification.
2. The installer completes and registers the CF2R installation certificate, including any charge or control checks.
3. An ECC-Rater, certified through an approved ECC-Provider, tests the system and registers the CF3R.
4. If a test fails, the contractor must fix the system until it passes.

What this means for your MEP plans and Title 24 report

The mechanical plan's equipment schedule must match the exact equipment modeled in the CF1R, including efficiency ratings that the model may claim as verified. Clear notes on the plans help your installer and ECC-Rater know what to expect. See mechanical plans, our earlier explainer on field verification (HERS, now ECC), and Title 24 reports.

Sources: energy.ca.gov, energy.ca.gov, energy.ca.gov, energy.ca.gov.