SEER vs SEER2: what changed and how to convert

If you compare an air conditioner sold in 2022 with one sold today, the efficiency numbers look as if they went down. A system that used to be advertised as "16 SEER" now shows about 15.2 SEER2. The equipment did not get worse. The test changed.

What SEER and SEER2 measure

SEER, the seasonal energy efficiency ratio, is the cooling a system delivers over a typical season divided by the electricity it uses, in BTU per watt-hour. A higher number means less electricity for the same cooling.

SEER2 measures the same thing under a revised federal test procedure (DOE Appendix M1, with the AHRI 210/240-2023 standard). It applies to equipment manufactured from 1 January 2023. The companion ratings changed at the same time:

• EER2 is cooling efficiency at a single hot condition (95 °F outdoors), useful for peak power.
• HSPF2 is a heat pump's seasonal heating efficiency.

The U.S. Department of Energy says the new ratings are not directly comparable with the old ones. That is why you need a conversion factor rather than comparing the numbers side by side.

How to convert

The industry conversion factors published by RESNET (developed by AHRI) are:

• Ducted split systems: SEER2 = SEER × 0.95; HSPF2 = HSPF × 0.85.
• Ducted packaged units: SEER2 = SEER × 0.95; HSPF2 = HSPF × 0.84.
• Ductless systems (mini-splits): SEER2 = SEER × 1.00; HSPF2 = HSPF × 0.90.

To go the other way, divide. A few ducted split examples:

• 14 SEER × 0.95 = 13.3 SEER2
• 16 SEER × 0.95 = 15.2 SEER2
• 20 SEER × 0.95 = 19.0 SEER2
• 8.8 HSPF × 0.85 = 7.5 HSPF2

If you are not sure what type of equipment you have, RESNET says to use the ducted split factors.

These factors are averages for estimating. A specific model's certified rating, from the manufacturer or the AHRI Directory, is always better than a converted number.

The 2023 federal minimums

Since 2023, new central air conditioners and heat pumps must meet these minimums:

• Split heat pumps, nationwide: 14.3 SEER2 and 7.5 HSPF2.
• Split air conditioners in the North: 13.4 SEER2.
• Split air conditioners in the Southeast: 14.3 SEER2 below 45,000 BTU/h, or 13.8 SEER2 at 45,000 BTU/h and above.
• Split air conditioners in the Southwest: the Southeast SEER2 values plus an EER2 minimum. That is 11.7 EER2 below 45,000 BTU/h and 11.2 EER2 at 45,000 BTU/h and above, or 9.8 EER2 if the unit reaches 15.2 SEER2 or more.

The Southwest is Arizona, California, Nevada and New Mexico. The Southeast covers Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, the District of Columbia, Puerto Rico and the other U.S. territories. The North is every other state.

In the North the rule applies by date of manufacture. In the Southeast and Southwest the regional air conditioner rule applies by date of installation. There, an air conditioner that misses the regional minimum cannot be installed, even if it was manufactured before the rule began.

What the rating means for your bill

Seasonal energy is roughly the cooling delivered divided by SEER2. Take a 3-ton system (36,000 BTU/h) that runs the equivalent of 1,200 full-load hours a year, with electricity at 18.31¢/kWh (the U.S. residential average for July 2026, per EIA):

1. Old 10 SEER system = about 9.5 SEER2. 36,000 × 1,200 ÷ 9.5 ÷ 1,000 = 4,547 kWh, about $833 a year.
2. New 16 SEER2 system: 36,000 × 1,200 ÷ 16 ÷ 1,000 = 2,700 kWh, about $494 a year.
3. Difference: about $338 a year.

Your numbers will depend on your climate, run time and electricity price. The SEER2 savings calculator does this conversion for you and takes either rating, and the AC electricity cost calculator estimates running cost from SEER2 or EER2.

Key points

• SEER2, EER2 and HSPF2 replaced SEER, EER and HSPF for equipment made from 2023 under a new test procedure.
• The new numbers are lower for the same equipment and are not directly comparable with the old ones.
• For ducted split systems, SEER2 ≈ SEER × 0.95 and HSPF2 ≈ HSPF × 0.85.
• Federal minimums vary by region and product type; in the South they apply by date of installation.
• Compare specific models using their certified SEER2 ratings whenever you can.

Sources

• 2023 Central Air Conditioner Standards — FAQ, U.S. DOE Office of Energy Efficiency & Renewable Energy.
• 10 CFR 430.32 — Energy and water conservation standards, Code of Federal Regulations (Cornell LII).
• MINHERS Addendum 71i — SEER2 and HSPF2 Conversions, RESNET (factors developed by AHRI).
• Electric Power Monthly, Table 5.6.A, U.S. Energy Information Administration.