SEER2
The federal rating for how much cooling an AC or heat pump delivers per unit of electricity across a season — the tougher test that replaced SEER on January 1, 2023.
SEER2 (Seasonal Energy Efficiency Ratio 2) measures cooling output per unit of electricity over a full season, for both central air conditioners and heat pumps. It replaced the older SEER metric on January 1, 2023 under a tougher test procedure that runs five times the duct static pressure — closer to how real ducted systems perform. The practical effect: a given unit's SEER2 rating reads about 4.5% lower than its old SEER number (SEER2 ≈ SEER × 0.95), so a "16 SEER" unit and a "15.2 SEER2" unit are roughly the same hardware.
The federal minimum is about 13.4 SEER2 in northern states and 14.3 in the South, and 2026 equipment clusters into three bands: standard (~15.2), high (~17), and premium (20+, variable-speed). Stepping up a tier adds roughly 18% (high) or 40% (premium) to the AC or heat-pump equipment cost — worth it mainly in hot climates or on heat pumps that run hard both seasons.