SEER2 (Seasonal Energy Efficiency Ratio 2) measures how efficiently an air conditioner or heat pump cools over an entire season. It is calculated by dividing total cooling output (in BTU) by total electrical energy consumed (in watt-hours) across a range of outdoor temperatures from 65°F to 104°F. A higher number means less electricity used per unit of cooling.
SEER2 replaced the original SEER metric on January 1, 2023, when the U.S. Department of Energy mandated updated testing standards for all newly manufactured residential cooling equipment.
What Changed From SEER to SEER2
The original SEER test ran equipment against 0.1 inches of water gauge (w.g.) of external static pressure, simulating almost no duct resistance. Real homes rarely match that. The updated M1 blower test procedure raises external static pressure to 0.5" w.g., roughly five times higher, to reflect the airflow resistance that ductwork, filters, and fittings create in a typical installation.
Because the test is harder, SEER2 ratings come out about 4.7% lower than SEER ratings for the same piece of equipment. A unit that scored 16 SEER under the old method lands around 15.2 SEER2 under the new one. The equipment did not get worse. The yardstick got more honest.
Federal Minimum SEER2 by Region
Region |
Split System AC |
Split System Heat Pump |
Packaged Systems |
North |
13.4 |
14.3 |
13.4 |
Southeast and Southwest (< 45k BTU) |
14.3 |
14.3 |
13.4 |
Southeast and Southwest (≥ 45k BTU) |
13.8 |
14.3 |
13.4 |
Any system installed below the regional minimum is out of compliance with federal efficiency standards.
SEER2 vs. EER2
SEER2 averages performance across a full cooling season. EER2 (Energy Efficiency Ratio 2) measures performance at a single peak condition: 95°F outdoors, 80°F indoors, 50% humidity. In hot climates where the system runs near full capacity for long stretches, EER2 can be the more telling number. A fuller breakdown of how these air conditioner efficiency ratings relate to each other and to real-world energy costs helps when comparing units side by side.
How SEER2 Applies to Ductless Systems
Mini-splits and ductless heat pumps carry SEER2 ratings just like ducted equipment. Many inverter-driven ductless units score well above federal minimums because variable-speed compressors adjust output to match the load rather than cycling on and off. Ratings of 20+ SEER2 are common in the ductless category, though actual performance still depends on installation quality, refrigerant charge, and how the system is operated day to day.