Quick answer
SEER2 is the cooling output over a typical season divided by the electricity used. EER2 is the same idea measured at a hot, steady condition. HSPF2 is the heating version for heat pumps. Since January 2023, the U.S. Department of Energy requires the newer M1 test procedure, which is why ratings now carry a '2'.
Why the numbers changed
The M1 test uses higher external static pressure to better match real duct systems. A system that was rated around 16 SEER might be rated closer to 15.2 SEER2. It isn't less efficient; the test is simply more realistic.
Which rating matters most in Los Angeles
Near the coast, cooling loads are mild, so SEER2 and quiet low-speed operation are often the priorities. In hotter areas like the San Fernando and San Gabriel Valleys, EER2 is worth a look because it reflects performance on very hot afternoons. For heat pumps, HSPF2 shows how well the system heats in winter.
Ratings only apply to matched systems
A rating is certified for a specific outdoor unit, indoor coil, and air handler combination listed in the AHRI directory. Mixing components or installing on leaky ducts can lower real-world efficiency. Ask for the AHRI reference number on your estimate.
