SEER2 is the cooling-efficiency rating for a mini-split's heat pump — the seasonal cooling it delivers divided by the electricity it draws. Higher is more efficient. On January 1, 2023 it replaced the older SEER number under a tougher U.S. Department of Energy test (Appendix M1) that runs the equipment against realistic airflow resistance, so SEER2 figures land roughly 4–5% below the old SEER rating for the same hardware (about 15 SEER ≈ 14.3 SEER2). Old SEER and new SEER2 numbers are not interchangeable when you compare quotes.
The federal floor for a heat pump is 14.3 SEER2, and unlike straight-cool air conditioners — which carry different minimums by region — heat pumps use a single national standard. That floor is the bottom of the market, not a target. Inverter-driven ductless mini-splits are among the most efficient systems sold, typically rated from the mid-teens past 30 SEER2 on single-zone models. The ENERGY STAR cutoff for ductless equipment is 15.2 SEER2 — above the federal minimum but below what a good inverter unit actually achieves.
Two cautions when reading SEER2 on a proposal. First, the rating belongs to a matched outdoor-plus-indoor combination listed in the AHRI directory, not to the outdoor unit alone — ask for the AHRI reference number. Second, a high SEER2 only pays off if the system is sized and installed correctly; an oversized or undercharged unit never reaches its rated efficiency in your home.