As of January 1, 2026, every heat pump installed in California requires refrigerant charge verification — new construction and alterations, in all 16 climate zones (2025 Standards Table 150.1-A and §150.2(b)1Fii). Air conditioners still require it in Climate Zones 2 and 8–15. There is no longer a heat pump installation where you can assume it doesn’t apply.
How the charge gets verified depends on the equipment. For a lot of systems, it also depends on when you call your HERS/ECC Rater.
Which verification method applies
Subcooling (RA3.2.2) — the normal method for ducted split systems with a TXV or EXV. The system is installed, charged and running, and the measured subcooling is compared to the manufacturer’s target. It needs weather: outdoor air at 55°F or above and return air at 70°F or above. Some inverter systems — certain Rheem/Ruud and Bosch models, for example — have a built-in charge mode that holds the compressor steady, which makes subcooling possible on those units.
Superheat (RA3.2.2) — only for systems with a fixed metering device (piston). Rarely seen in the field today.
Witnessed weigh-in (RA3.2.3.1 and RA3.2.3.2) — required for mini-splits and most inverter-driven heat pumps, which can’t hold the stable operating conditions subcooling or superheat need. The HERS/ECC Rater has to be physically on site, observing the procedure in real time. The weigh-in is also the method used when it’s below 55°F outside.
What the witnessed weigh-in involves
The installer performs the procedure; the HERS/ECC Rater observes and records it:
Evacuate the system to 500 microns or less.
Isolate and hold a decay test — no more than a 300-micron rise over 5 minutes.
Weigh in the refrigerant on a calibrated digital scale (accurate to ±0.5 oz).
Adjust the charge for the actual installed line set length, per the manufacturer’s installation manual.
Installers — have these computed and ready before the rater arrives:
Factory charge (lbs/oz), from the equipment nameplate
Factory line set length the charge is designed for
Actual installed line set length — measured, not estimated
Liquid line diameter
Charge correction rate (oz/ft), from the installation manual
Calculated charge adjustment for the installed line set
The most common failure: calling after the install
The rater can’t certify a weigh-in after the fact. If the evacuation, decay test and weigh-in were not witnessed in person, the procedure has to start over from zero. The entire system must be recovered and evacuated — including the compressor — then recharged with the rater present (RA3.2.3.1.1.2, Weigh-in Total Charge).
That is costly, and on a brand-new inverter system it can actually damage the equipment, even when a qualified technician does everything right. It is not recommended.
Why recovering a commissioned inverter system is risky
Compressor oil loss. Oil circulates through the whole system during operation — and on inverter systems running at low speed, more of it settles in the line set and indoor coil. During recovery that oil is carried into the recovery cylinder and doesn’t come back with the new charge (ASHRAE Handbook — Refrigeration, Ch. 9). Some manufacturers’ inverter compressor oil isn’t sold separately.
Moisture contamination. The POE/PVE oils used with R-410A and R-32 absorb moisture on contact with air and chemically bond with it. Evacuation alone can’t pull it back out, and the result is acid that attacks the compressor and clogs electronic expansion valves (ASHRAE Handbook — Refrigeration, Ch. 6).
Thermal shock. As pressure drops during recovery, R-410A’s saturation temperature falls toward −50°F. That puts the electronic expansion valve and the factory-brazed joints inside the outdoor unit through a rapid, extreme temperature swing.
How to avoid it
Schedule your HERS/ECC Rater before the system is charged — not after. Contractors: put the weigh-in on the schedule at the same time you schedule the equipment install, and we’ll coordinate directly with your HVAC installer to be on site when the system is charged. Homeowners: if your project includes a heat pump or mini-split, ask your contractor who the HERS/ECC Rater is and when the weigh-in is scheduled.
More on how each method works, and the code language behind it: Refrigerant Charge Verification. Ready to schedule? Book now.
Sources
2025 California Building Energy Efficiency Standards, Table 150.1-A, §150.1(c)7A, §150.2(b)1F — energy.ca.gov
2025 Reference Appendices RA3.2.2, RA3.2.3.1 and RA3.2.3.2 — energy.ca.gov
ASHRAE Handbook — Refrigeration, Chapter 9 (Refrigerant Containment, Recovery, Recycling and Reclamation) and Chapter 6 (Refrigerant System Chemistry)
ACHR News, “Oil Loss and What Causes It” and “The Effect of Moisture on POEs” — achrnews.com
HVAC School, “32° Saturation (Evap Temperature),” Bryan Orr — hvacrschool.com