What is refrigerant charge verification, and does my ADU heat pump need it?

Refrigerant charge verification confirms your heat pump has the right amount of refrigerant after installation, because too much or too little cuts efficiency and capacity and can lead to early compressor failure. Under the 2025 Energy Code, new heat pumps need it in all 16 climate zones, including ductless mini-splits, and an ECC rater (formerly HERS rater) verifies it.

Where the requirement comes from

• Table 150.1-A lists refrigerant charge verification as required for heat pumps in every climate zone, and for air conditioners in zones 2 and 8 through 15.
• Section 150.1(c)7A applies it to air-source heat pumps, including ducted split systems, small duct high velocity systems and mini-split systems.
• The CEC's ADU FAQ lists refrigerant charge in all climate zones among the common ECC verifications for mini-split and multi-split systems, and CEC training materials show the same requirement for completely new systems in ADU additions.

Two ways to verify

1. Standard charge test. The installer and rater measure superheat or subcooling with gauges and temperature sensors while the system runs in cooling mode. It needs suitable outdoor conditions, and ducted systems must also show at least 350 cfm per ton of airflow.
2. Weigh-in method. The installer charges by weight, based on the equipment and line set size and length and the manufacturer's specifications. For systems that cannot use the standard test, such as many ductless mini-splits, the CEC's Compliance Manual says the rater verifies by observing the installer's weigh-in as it happens.

Systems verified by weigh-in cannot use group sampling, so plan for the rater to be on site during charging.

Cold weather and DIY units

• Below 55°F outdoors, the code allows alternatives, such as the installer weigh-in paired with a compliant thermostat, or waiting for warmer weather with written notice that the charge has not yet been verified.
• Pre-charged "DIY" mini-splits are not exempt. The Compliance Manual explains that connecting the indoor unit, outdoor unit and line set alters the system, so the weigh-in protocol applies.

Paperwork

The installer completes the Certificate of Installation (CF2R), and the rater completes the Certificate of Verification (CF3R). Both are registered with an ECC provider, and CEC training materials tell inspectors to confirm registration at final inspection.

What it means for your mechanical plan

• Note the ECC verification requirement on the mechanical sheets so the installer schedules the rater.
• List exact indoor and outdoor model numbers so the rater can match equipment to the CF1R.
• For ducted systems, show the measurement access holes and static pressure probe location that testing requires.

More on the process: HERS (now ECC) testing and Title 24 HVAC requirements for new ADUs.

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