SEER2 (Seasonal Energy Efficiency Ratio 2) is the cooling-efficiency rating for central air conditioners and heat pumps, updated in 2023. Like the original SEER, it tells you how much cooling you get for the electricity used over a summer — higher is better and means lower bills. The 2 marks a tougher, more realistic test.
The change is the test, not the equipment. Starting January 1, 2023, the Department of Energy began testing systems against higher airflow resistance (0.5 inches of water gauge, which mimics real home ductwork). Under this harder test, ratings came out lower. An air conditioner that earned SEER 14 before 2023 reads about SEER2 13.4 today, even though nothing inside it changed. So you can only compare SEER2 numbers to other SEER2 numbers.
The 2026 federal minimums are SEER2 14.3 across the southern US (Florida, Texas, Arizona, California, Georgia, Nevada, New Mexico, and similar hot states) and SEER2 13.4 in the north. The split reflects how much harder air conditioners work in hot climates. A unit that just meets the minimum is legal to install, but it is the floor, not a good value where you run AC half the year.
For rebates, aim higher. Most utility programs require SEER2 15.2 or above to pay out, so a minimum-efficiency system earns nothing back. Moving from SEER2 14.3 to SEER2 18 cuts cooling electricity use by roughly 20% (the ratio of the two numbers) for the same comfort — the payback depends on your local power rate and how many months you run the system.