In 2023 the U.S. rating system for central AC and heat pumps moved from SEER to SEER2. Salespeople treated it like a new logo. It is a harder test. The number got smaller for the same machine.
If you compare a 2018 brochure SEER 16 to a 2026 SEER2 16, you are not comparing the same test. The SEER2 unit is the more efficient one.
What SEER always was
SEER is seasonal energy efficiency ratio: cooling output over a season divided by watt-hours in. Higher means less electricity for the same cooling, under the test conditions. It was never your exact bill. It was a lab ranking.
What changed in the M1 test
SEER2 uses a test (often called M1) that assumes more external static pressure — closer to a real ducted house and a real filter. The old test was too optimistic. Units looked better on paper than they performed attached to actual ducts.
Because the fan works harder in the new test, the same hardware posts a lower number. A rough mental conversion many people use is that old SEER is often around 5% higher than SEER2 for a similar unit. Treat that as a sketch, not a law. Always compare SEER2 to SEER2, and look at the AHRI certificate for the exact outdoor + indoor pair.
Regional minimums
The Southwest, including California, has higher minimum efficiencies than some other regions. A 'legal' system here is not the same as a legal system in a milder-code market. If someone wants to install a unit that does not meet current California requirements, that is not a bargain. That is a permit and inspection problem.
What SEER2 does not tell you
- Whether the system is sized correctly. A high-SEER2 unit that short-cycles still wastes money and comfort.
- Duct leakage. Efficiency at the equipment is not efficiency in the bedroom.
- Charge and airflow. A 5% charge error can erase a SEER2 step.
- Your electric rate or solar. The dollar savings depend on how you buy power.
Is the jump from 14.3 to 18 worth it?
Sometimes. At SCE rates, more hours of cooling make the premium pay back faster. A shaded 1,400 sq ft house that barely runs may never earn back a top-tier inverter. A two-story west-facing house that runs all afternoon might.
Also look at HSPF2 if it is a heat pump — that is the heating-season cousin. Cooling-only shoppers can ignore it. Dual-fuel and heat-pump shoppers should not.
How to read a quote
You want the AHRI reference number, SEER2 (and EER2), matched indoor model, and a Manual J. SEER2 without a match is a catalog page, not a system.
We will translate the rating into an estimated kWh number for your house if you want it. That is more honest than circling the biggest SEER2 on the page.