Central AC System GuideSEER2 is the current measure of central AC cooling efficiency, and it replaced SEER on January 1, 2023 under a revised Department of Energy testing procedure. Trane defines it as total seasonal heat removed divided by total seasonal electricity used, and regional rules set minimums of 13.4 SEER2 in the North and 14.3 SEER2 in the South for split systems. A higher SEER2 number means a more efficient system.
What SEER2 measures
SEER stands for Seasonal Energy Efficiency Ratio, and Trane describes SEER2 as the updated version of that rating for air conditioners and heat pumps. It is defined as the ratio of total heat removed during the cooling season divided by the total electric energy the unit uses over the same period.
Because it is a seasonal measure, SEER2 reflects real operating conditions across a cooling season rather than a single test point. A higher SEER2 value means the system delivers more cooling per unit of electricity, which translates into lower operating cost.
The 2023 change from SEER to SEER2
The rating changed at the start of 2023. Trane states the Department of Energy mandated SEER2 implementation on January 1, 2023, and HVACDirect confirms that new regional minimums took effect the same date.
The change was as much about testing as naming. Trane explains that SEER2 uses a new M1 blower testing procedure that raises the static pressure used in the lab from 0.1 inches water gauge to 0.5 inches, better reflecting real-world duct conditions. Because the test is harder, a system's SEER2 number is somewhat lower than its old SEER number on the same equipment.
Regional minimums: 13.4 North, 14.3 South
New systems must meet a minimum that varies by region. HVACDirect states that northern states require split system air conditioners to meet 13.4 SEER2, while southeastern states require 14.3 SEER2 for split systems. Trane gives the same split, listing 13.4 or higher for air conditioners in the North and 14.3 or higher for split systems in the Southeast and Southwest under 45,000 BTU.
The regions also differ in how the rule applies. HVACDirect notes that in the Southern and Southwestern regions all units installed after January 1, 2023 must meet the new standards, while northern states still allow pre-2023 manufactured units to be installed. Southwestern states additionally impose EER2 requirements of 11.7 for systems under 45,000 BTU and 11.2 for larger systems.
ENERGY STAR and where efficiency pays off
Above the legal minimum sits ENERGY STAR certification. The Department of Energy Federal Energy Management Program lists ENERGY STAR central air conditioners at 15.2 SEER2 across regions, a step above the regional floors.
Higher efficiency saves energy where cooling runs long. The FEMP illustrates the payoff with a 36,000 Btu/h unit in southeastern states that uses about 8,074 kWh per year as an ENERGY STAR model versus 9,159 kWh for a less efficient one, a difference of roughly $119 per year at 11 cents per kWh. It also reports the best available models can save up to $6,724 over their lifetime in hot-humid states.