What SEER2 measures
SEER2 is the total heat removed from the home over the cooling season, in Btu, divided by the electricity the unit used over the same season, in watt-hours. The definition is the same idea as the older SEER, which the Energy Information Administration describes as Btu of cooling output divided by watt-hours of electric input during normal annual use. The difference is the test. The federal test method in appendix M gives SEER; the newer appendix M1 gives SEER2, along with EER2 and HSPF2. Standards for equipment made on or after January 1, 2023 are written in SEER2, and the yellow EnergyGuide label on a new central air conditioner or heat pump shows SEER2.
Because the two tests are not the same, do not compare a SEER figure on an old system with a SEER2 figure on a new one as if they were one scale. Compare new units with each other on SEER2.
The federal minimums
The national floor depends on the product class. For units made on or after January 1, 2023:
| Product | SEER2 | HSPF2 |
|---|---|---|
| Split air conditioner | 13.4 | none |
| Split heat pump | 14.3 | 7.5 |
| Single-package air conditioner | 13.4 | none |
| Single-package heat pump | 13.4 | 6.7 |
| Small-duct, high-velocity | 12 | 6.1 |
| Space-constrained AC | 11.7 | none |
| Space-constrained heat pump | 11.9 | 6.3 |
For context, in 1992 the appliance standards required a SEER of 10 for split-system air conditioners and heat pumps, on the older test. Today's floors are in SEER2, so the two numbers are not on the same scale.
Regional rules for air conditioners
Split-system air conditioners installed on or after January 1, 2023 in the Southeast or Southwest must meet higher figures than the national floor:
- Under 45,000 Btu/h: at least 14.3 SEER2, and an EER2 of 11.7, or 9.8 for models rated 15.2 SEER2 or more.
- 45,000 Btu/h or more: at least 13.8 SEER2, and an EER2 of 11.2, or 9.8 for models rated 15.2 SEER2 or more.
The rule defines the Southeast as Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, Puerto Rico, South Carolina, Tennessee, Texas, Virginia, the District of Columbia and the US territories. The Southwest is Arizona, California, Nevada and New Mexico. Everywhere else the national 13.4 applies. The EnergyGuide label on a central air conditioner says whether the unit may be installed in all states or lists the states where it may be, with a map; see how to read an EnergyGuide label.
From SEER2 to kWh and dollars
The factor of 1,000 turns watt-hours into kWh. Take a home whose system removes 30 million Btu of heat in a season, an assumed figure for the example, and price it at the August 2026 US average of 18.16 cents per kWh from the Energy Information Administration:
| SEER2 | kWh a year | Cost a year | vs 14.3 |
|---|---|---|---|
| 13.4 | 2,239 | $407 | $26 more |
| 14.3 | 2,098 | $381 | $0 less |
| 15.2 | 1,974 | $358 | $23 less |
| 17 | 1,765 | $320 | $61 less |
| 20 | 1,500 | $272 | $109 less |
Two things stand out. The steps shrink as the rating rises: going from 14.3 to 17 saves more than going from 17 to 20, because energy is the load divided by the rating. And the saving scales with the load and the price. A home that cools twice as much, or pays twice the rate, saves twice the dollars at each step. Over 10 years the step from 14.3 to 20 in this example is worth about $1,086 at today's price.
If you do not know your seasonal Btu, you can work per million Btu of cooling, which makes it easy to scale:
| SEER2 | kWh per million Btu | Cost at 18.16¢ |
|---|---|---|
| 13.4 | 74.6 | $13.55 |
| 14.3 | 69.9 | $12.70 |
| 15.2 | 65.8 | $11.95 |
| 17 | 58.8 | $10.68 |
| 20 | 50.0 | $9.08 |
The BTU calculator estimates a room's cooling need in Btu per hour, the energy converter turns Btu into kWh (1 kWh is 3,412 Btu), and the electricity cost calculator prices the result at your own rate.
Worked example: two quotes
Say a contractor offers a 14.3 SEER2 system and a 17 SEER2 system, and your home is in a hot area where the system removes about 45 million Btu a season. Your utility charges 25 cents per kWh. The first unit uses 3,147 kWh a year and the second 2,647 kWh. The difference, 500 kWh, is worth $125 a year, or $1,499 over 12 years if the price stays where it is. If the higher-rated system costs more than that up front, it does not pay for itself on energy alone in that time. Run the same numbers with your own load and rate before you decide, because a mild climate or a low rate can cut the saving to a fraction of this.
EER2: efficiency on the hottest days
SEER2 averages a whole season. EER2 is the ratio of cooling delivered to electric power used at one hot condition, 95 °F outdoors. It tells you how much power the unit draws on the hottest afternoons. Power draw at that point is the capacity divided by EER2. For a 36,000 Btu/h unit:
| EER2 | Watts at 95 °F |
|---|---|
| 9.8 | 3,673 |
| 11.2 | 3,214 |
| 11.7 | 3,077 |
| 13 | 2,769 |
HSPF2: the heating side of a heat pump
HSPF2 is the heating season version for heat pumps: Btu of heat delivered over the season divided by watt-hours used. The same division works. For 30 million Btu of heat, a heat pump at HSPF2 6.7 uses 4,478 kWh, at 7.5 it uses 4,000 kWh, and at 9 it uses 3,333 kWh. Whether that beats a gas furnace depends on fuel prices; heat pump vs gas furnace cost runs that comparison.
How to use the rating when you buy
- Confirm the unit meets the minimum for your state, especially in the Southeast and Southwest.
- Estimate your seasonal cooling in Btu, or work per million Btu with the second table.
- Run the formula for each quote and multiply the yearly difference by the years you plan to stay.
- Compare the savings with the price difference between the quotes.
- Ask for the certified rating of the outdoor and indoor units as a combination, since the regional rules look at certified combinations, not the outdoor unit alone.
Frequently asked questions
What is the difference between SEER and SEER2?
Both are seasonal cooling efficiency ratings in Btu of cooling per watt-hour. SEER comes from the older test procedure, appendix M, and SEER2 from the newer appendix M1, which federal standards have used for equipment made since January 1, 2023. Because the test conditions differ, compare SEER2 only with SEER2.
What is the minimum SEER2 for a new central air conditioner?
For split-system air conditioners made on or after January 1, 2023, the national minimum is 13.4 SEER2. In the Southeast and Southwest, a split system under 45,000 Btu per hour installed on or after that date needs at least 14.3 SEER2, and one of 45,000 Btu per hour or more needs 13.8.
How much does a higher SEER2 save?
Divide your seasonal cooling in Btu by each SEER2 times 1,000 to get kWh, then multiply by your rate. In this guide's example of 30 million Btu a season at 18.16 cents per kWh, going from 14.3 to 17 SEER2 saves about $61 a year. The saving grows with how much you cool and with your electricity price.
What do EER2 and HSPF2 mean?
EER2 is the cooling rate divided by the electric power used, in Btu per watt-hour, at one hot test condition of 95 °F outdoors. HSPF2 is the heating season counterpart for heat pumps: Btu of heat delivered over a heating season divided by watt-hours used.
Does the regional standard apply to heat pumps?
The extra regional SEER2 and EER2 requirements in the federal rule apply to split-system and single-package air conditioners installed in the Southeast or Southwest. Split-system heat pumps have a single national minimum of 14.3 SEER2 and 7.5 HSPF2.
Sources
- 10 CFR 430.32(c) (eCFR): SEER2 and HSPF2 minimums for products made on or after January 1, 2023; regional SEER2 and EER2 standards for air conditioners installed in the Southeast and Southwest; the state lists; EER2 at 95 °F
- 10 CFR 430, subpart B, appendix M1 (eCFR): uniform test method that determines SEER2, HSPF2 and EER2
- ENERGY STAR Program Requirements for Heat Pumps, Rev. February 2026: definitions of SEER2, EER2 and HSPF2 in Btu per watt-hour; appendix M1 gives SEER2, appendix M gives SEER
- US Energy Information Administration, Glossary: seasonal energy efficiency ratio (minimum SEER of 10 for split systems in 1992)
- US Energy Information Administration, British thermal units (1 kWh = 3,412 Btu)
- 16 CFR 305.20 (eCFR): EnergyGuide labels for central air conditioners and heat pumps show SEER2 and HSPF2, regional statements and a map
- US Energy Information Administration, Electric Power Monthly, table 5.6.A: average residential price, August 2026 (18.16 cents per kWh)