SEER2 (Seasonal Energy Efficiency Ratio 2) is the U.S. Department of Energy rating for the cooling efficiency of central air conditioners and heat pumps: total seasonal cooling in BTUs divided by the watt-hours of electricity used. It replaced SEER on January 1, 2023, under a test with higher duct resistance, so it reads lower for identical equipment.
Why it matters to you
For the same cooling, electricity use scales inversely with SEER2: moving from 14 to 18 SEER2 uses about 22% less electricity (1 − 14/18). In hot regions where the air conditioner runs most of the year, that ratio applies to far more hours than in mild ones.
Practical guidance
Compare quotes SEER2 to SEER2, not an old SEER figure against a new SEER2 one. Confirm the rating in the AHRI Directory for the exact outdoor unit and indoor coil or air handler being installed, since a mismatched coil can leave a system short of its listed rating.
SEER2 tiers for split central air conditioners
| Tier | SEER2 | EER2 | Electricity vs. 13.4 SEER2 (arithmetic, not a bill estimate) |
|---|---|---|---|
| Federal minimum, North region | 13.4 | No regional minimum | Baseline |
| Federal minimum, Southeast and Southwest regions (under 45,000 BTU/h) | 14.3 | Minimum applies in the Southwest only | About 6% less |
| ENERGY STAR (split air conditioner) | 15.2 | 12.0 | About 12% less |
| High efficiency (often two-stage) | 18 | Varies by model | About 26% less |
| Premium (variable-speed) | 20 | Varies by model | About 33% less |
What is EER2, and how is it different from SEER2?
EER2 (Energy Efficiency Ratio 2) measures cooling efficiency at a single hot condition, 95°F outdoors, rather than averaged across a cooling season. SEER2 describes typical seasonal use, while EER2 describes how the system holds up at peak heat. Homes in very hot, dry climates spend more hours near that peak, which is why the federal Southwest region sets EER2 minimums as well as SEER2 minimums.
What is the minimum SEER2 for a new central air conditioner?
Federal minimums that took effect on January 1, 2023 vary by region. Split central air conditioners must reach 13.4 SEER2 in the North and 14.3 SEER2 in the Southeast and Southwest (13.8 SEER2 for systems of 45,000 BTU/h and larger), and split heat pumps must reach 14.3 SEER2 nationwide. The Southwest region, which includes Arizona, Nevada and New Mexico, adds EER2 minimums for air conditioners.
How much less electricity does a higher SEER2 system use?
For the same cooling, electricity use scales inversely with the rating. Going from 13.4 to 16 SEER2 uses about 16% less electricity (1 − 13.4/16), and going from 14 to 18 SEER2 uses about 22% less (1 − 14/18). These are ratios under standard test conditions, not an estimate for any specific home.
Is the highest SEER2 always worth choosing?
Not automatically. Each additional point saves a smaller share than the one before it, and a high-SEER2 system on leaky ducts or with the wrong refrigerant charge will underperform a mid-range system installed correctly. Climate, yearly runtime and how long you plan to stay in the home matter as much as the rating itself.