Central AC System GuideA split-system central air conditioner is the most common residential setup in the United States. The outdoor unit holds the compressor and condenser coil, while a separate indoor coil sits with the air handler or furnace. The two are joined by refrigerant piping and are only rated when paired as a matched combination.
How a split system is arranged
In a split system the equipment is deliberately divided into two assemblies. The outdoor cabinet contains the compressor and the coil that rejects heat outside, and a second indoor coil pulls heat out of the household air. Energy Star's federal specification defines the type directly.
Federal purchasing guidance treats split systems as one of three residential central AC formats, alongside single-package and gas/electric package units, for cooling capacities under 65,000 Btu per hour.
Why the condenser and coil must be matched
A split system only earns its rated efficiency when the outdoor unit is paired with an appropriate indoor coil. Mixing an old coil with a new condenser, or vice versa, breaks the rating the equipment was certified against.
Energy Star states the requirement plainly, and the federal tax-credit rules likewise set thresholds that a split system as a whole must meet, not the outdoor box alone.
What SEER2 measures and the 2023 test change
SEER2 is the cooling efficiency metric used since 2023. It replaced the older SEER value after the Department of Energy revised the test procedure to better reflect real duct conditions.
The updated M1 test raises the external static pressure the equipment works against, so the same hardware reads a lower number under SEER2 than it did under SEER.
Minimum SEER2 by region for split systems
The 2023 standards set different floors for the northern and southern United States because cooling loads differ by climate. A split-system air conditioner sold in the North must clear a lower SEER2 than one sold across the southern regions.
In the North the split-system floor is 13.4 SEER2, while southeastern states hold smaller units to 14.3 SEER2 and larger units to a slightly lower figure.