What Is a SEER Rating and How Is It Different From a SEER2 Rating?

Updated October 2026

SEER2 is the current way air conditioners and heat pumps are rated for cooling efficiency in the United States. It replaced the original SEER rating on January 1, 2023, when the Department of Energy (DOE) switched to a tougher test procedure called M1. A system's SEER2 number is slightly lower than its old SEER number (roughly SEER × 0.95), but the rule hasn't changed: the higher the rating, the less electricity the system uses to cool your home.

SEER2 ratings apply to central air conditioner and heat pump condensers as well as ductless mini splits. Here's what the numbers mean, how to compare old and new ratings, and what to look for when you shop.

What Is a SEER Rating?

SEER stands for Seasonal Energy Efficiency Ratio. It's the total cooling a system delivers over a typical cooling season (in BTUs), divided by the total electricity it uses over that season (in watt-hours). Think of it as a miles-per-gallon rating for air conditioning. A system with a higher SEER delivers the same cooling for less electricity.

Like a fuel economy sticker, SEER is measured in a lab under standard conditions. Your real-world efficiency also depends on correct sizing, a good installation, ductwork condition and your climate.

What Is SEER2, and Why Did It Replace SEER?

SEER2 is the same basic ratio measured with the DOE's updated M1 test procedure, required for equipment ratings since January 1, 2023. The biggest change is external static pressure, which is the resistance a system's blower works against when pushing air through ducts, filters and registers.

The old test assumed very little resistance, which isn't how most real homes work. According to AHRI, the M1 test raises the external static pressure used in testing by up to five times to better reflect field conditions. Because the system works harder in the test, it earns a lower number. The equipment itself didn't get less efficient; the yardstick got more realistic.

The same change created two companion ratings, EER2 and HSPF2, which replaced EER and HSPF.

SEER vs. SEER2: How to Compare the Numbers

The DOE notes that SEER and SEER2 are similar but not directly comparable, so always compare SEER2 to SEER2 when shopping. If you're looking at an older spec sheet, a handy rule of thumb is SEER2 ≈ SEER × 0.95:

These are approximations. The actual SEER2 rating for any model is on its spec sheet and in the AHRI Directory of certified ratings.

EER2 and HSPF2: The Other Two Numbers on the Label

• EER2 (Energy Efficiency Ratio 2) measures efficiency at peak load, with 95°F outdoors, when the system is working its hardest. The DOE points out that EER matters most in hot, dry climates with many high-temperature days.
• HSPF2 (Heating Seasonal Performance Factor 2) measures a heat pump's heating efficiency over a typical heating season. Higher HSPF2 means less electricity used for heating. If you're replacing a furnace or living somewhere with real winters, HSPF2 deserves as much attention as SEER2.

Federal Minimum SEER2 Requirements (Since 2023)

The DOE sets minimum efficiency standards, and for central air conditioners they vary by region. The North covers colder states. The Southeast includes states such as Texas, Florida, Georgia, the Carolinas, Tennessee and Kentucky. The Southwest is Arizona, California, Nevada and New Mexico.

The timing rules also differ. In the North, the standard depends on when a unit was manufactured. In the Southeast and Southwest, it depends on the installation date: any split-system AC installed there on or after January 1, 2023 must meet the new minimum.

What SEER2 Rating Should You Look For?

The federal minimum is a floor, not a target. Here's how our team thinks about it:

• Hot, long cooling seasons: Every extra point of SEER2 pays back faster when the AC runs most of the year. In the Southwest, check EER2 too.
• Cold winters: If a heat pump will be your main heat source, look closely at HSPF2 and at models built for cold climates. Our heat pump vs. AC guide explains the trade-offs.
• Mini splits vs. central systems: Ductless systems have no duct losses, and many of the mini splits we carry are rated above 20 SEER2. Central ducted heat pump systems in our catalog commonly fall in the mid-to-high teens.
• Look for ENERGY STAR: ENERGY STAR-certified models exceed the federal minimums. The label is a quick way to narrow your choices.
• Get the size right: A high-SEER2 system that's the wrong size will still waste energy and leave rooms uncomfortable. Start with our mini split sizing guide.

A note on incentives: the federal 25C tax credit ended for systems placed in service after December 31, 2025. Many state and utility rebate programs still set their own SEER2 and HSPF2 requirements, so check with your local utility before you buy.

How Much Can a Higher SEER2 Save?

Seasonal cooling energy is roughly the cooling delivered divided by SEER2. That makes comparisons simple. Say a system delivers 24 million BTUs of cooling in a season (a 2-ton system at about 1,000 full-load hours):

• At 14.3 SEER2: 24,000,000 ÷ 14.3 ≈ 1,680 kWh
• At 20 SEER2: 24,000,000 ÷ 20 = 1,200 kWh

That's about 28% less electricity for the same cooling. Multiply the difference by your electric rate to estimate yearly savings. This example is only an illustration, since your hours, climate and rates will differ, but the math shows why SEER2 matters more the more you run your AC.

The Bottom Line

SEER2 is the current, more realistic version of SEER. The numbers run slightly lower for the same equipment, so compare SEER2 to SEER2, check HSPF2 if you're buying a heat pump, and treat the federal minimum as a starting point. Then match the rating to your climate and get the sizing right.

Compare ratings across our mini splits and central AC and heat pump condensers, or read our HVAC buying guide for the full checklist. Our team can help you compare SEER2, HSPF2 and sizing for your home.