What is SEER2? It's the cooling efficiency rating used for central air conditioners, heat pumps and mini splits made for the US since January 1, 2023. The number tells you how much cooling you get for each watt-hour of electricity over a typical summer, so a higher SEER2 means a smaller power bill for the same comfort. Here's what it measures, why it replaced plain SEER, what the legal minimums are, and how much a higher rating actually saves.
Definition
What SEER2 Measures
SEER2 stands for Seasonal Energy Efficiency Ratio 2. It's the total cooling a system delivers over a modeled cooling season, in BTU, divided by the electricity it uses over that same season, in watt-hours. A 20 SEER2 unit moves 20 BTU of heat out of your house for every watt-hour it draws.
"Seasonal" is the key word. The test doesn't just run the unit flat out on a 95°F day. It mixes in milder conditions and part-load running, because that's how an air conditioner spends most of the summer. Variable-speed and inverter systems, which slow down instead of shutting off, tend to score well for exactly that reason.
The rating belongs to a matched system, the outdoor unit plus a specific indoor coil or air handler. Pair the same condenser with a different indoor unit and the certified number can change.
History
SEER vs SEER2: Why the Numbers Changed
On January 1, 2023 the Department of Energy switched to a new test procedure (called M1), and every rating after that date is published as SEER2, EER2 and HSPF2. The equipment didn't get worse overnight. The test got harder.
The big change is external static pressure, the resistance the blower has to push against. According to Trane's SEER explainer, the new test raised it from 0.1 to 0.5 inches of water column, up to five times higher, which is much closer to what real ductwork and filters put on a blower. More resistance means more fan power, so ducted systems post lower numbers under SEER2 than they did under SEER.
How much lower depends on the type of system. These are the conversion factors developed by AHRI and adopted by RESNET for home energy ratings (RESNET Addendum 71f):
| System type | SEER2 ÷ SEER | HSPF2 ÷ HSPF |
|---|---|---|
| Ducted split | 0.95 | 0.85 |
| Ducted packaged | 0.95 | 0.84 |
| Ductless (mini split) | 1.00 | 0.90 |
| Small-duct high-velocity | 1.00 | 0.85 |
So an old 16 SEER ducted split works out to about 15.2 SEER2. A ductless mini split has no ductwork to push against, and its cooling number carries straight across. That matters if you're comparing an older mini split spec sheet to a new one. Heating numbers still drop about 10% for ductless units.
Don't compare a SEER number to a SEER2 number head to head. Convert one of them first, or you'll think a ducted system is worse than it is.
Related Ratings
EER2 and HSPF2: The Other Two Numbers
- EER2 is efficiency at one hot, full-load condition instead of a whole season. It tells you how the unit does on the worst afternoons, which is why hot, dry states care about it. A system can have a great SEER2 and only an average EER2.
- HSPF2 (Heating Seasonal Performance Factor 2) is the heat pump version of SEER2: BTU of heat delivered per watt-hour over a modeled heating season. If you're buying a heat pump or a mini split to heat with, this is the number to look at.
For cold climates, neither SEER2 nor HSPF2 tells the whole story. Check how much heating capacity the unit keeps at 5°F, which is what ENERGY STAR's cold climate label looks at (more on that below).
Regulations
Federal Minimum SEER2 Ratings
The minimum efficiency for new central systems depends on where you live, and since 2023 it's set in SEER2. These are the split-system minimums in the federal rule (10 CFR 430.32):
| Equipment | North | Southeast | Southwest |
|---|---|---|---|
| Split AC under 45,000 BTU/h | 13.4 SEER2 | 14.3 SEER2 | 14.3 SEER2 + EER2 minimum |
| Split AC 45,000 BTU/h and up | 13.4 SEER2 | 13.8 SEER2 | 13.8 SEER2 + EER2 minimum |
| Split heat pump | 14.3 SEER2 and 7.5 HSPF2 everywhere | ||
The Southwest (Arizona, California, Nevada and New Mexico) adds an EER2 floor for split air conditioners: 11.7 EER2 under 45,000 BTU/h, or 11.2 at 45,000 and up, dropping to 9.8 for units rated at 15.2 SEER2 or higher. The Southeast covers most of the South, from Texas and Oklahoma east through Florida and up to Maryland and Delaware, plus Hawaii.
Any new mini split heat pump has to meet these minimums to be sold, and plenty are rated well above them. They matter more if you're replacing a central AC and trying to buy the cheapest legal option.
Certification
What SEER2 Earns an ENERGY STAR Label?
ENERGY STAR sets its bar above the federal minimum. For air-source heat pumps and central air conditioners, the current criteria are (ENERGY STAR key product criteria):
| Category | SEER2 | EER2 | HSPF2 |
|---|---|---|---|
| Split central AC | 15.2 | 12.0 | - |
| Split heat pump | 15.2 | 11.0 | 7.8 |
| Cold climate heat pump, ductless split | 15.2 | - | 8.5 |
| Cold climate heat pump, ducted split | 15.2 | - | 8.1 |
The cold climate label also requires a COP of at least 1.75 at 5°F, and the unit has to keep at least 70% of its 47°F heating capacity at 5°F. If you live somewhere with real winters, that second test is a better guide than any seasonal number.
Operating Cost
How Much Does a Higher SEER2 Save?
The math is simple enough to do on a napkin. Seasonal cooling in BTU, divided by SEER2, gives you watt-hours. Take a system that delivers 12,000 BTU/h (one ton) for 1,000 full-load hours in a summer, which is 12 million BTU of cooling, and assume electricity at $0.17/kWh:
| Rating | kWh per season | Cost at $0.17/kWh |
|---|---|---|
| 14.3 SEER2 (federal minimum) | ~839 | ~$143 |
| 15.2 SEER2 (ENERGY STAR) | ~789 | ~$134 |
| 20 SEER2 | 600 | $102 |
| 25 SEER2 | 480 | ~$82 |
Two things jump out. First, the savings shrink as the number climbs: going from 14.3 to 20 saves about 239 kWh, but 20 to 25 only saves 120 more. Second, the dollars scale with how hard you run the system. Double the hours (a long, hot Southern summer) or the tonnage and the gap doubles too. Plug in your own rate from your electric bill; the tonnage-to-BTU math is in our AC tonnage guide.
A high rating only pays off if the system is the right size. An oversized unit short cycles, and ENERGY STAR notes an air conditioner is least efficient in the first minutes of each cycle, so it wastes power while also leaving the room clammy. Those are the signs your AC is the wrong size. Getting the load right with a mini split sizing calculator or a full ACCA Manual J is worth more than a couple of extra SEER2 points.
How To
Where to Find a Unit's SEER2 Rating
- The spec sheet or product page. Look for SEER2, EER2 and HSPF2 listed together. If you only see "SEER," the listing is either old or quoting a pre-2023 rating.
- The yellow EnergyGuide label. New central ACs and heat pumps carry one with the efficiency rating.
- The AHRI Directory. Search by model number to see the certified rating for the exact outdoor and indoor pairing. Contractors and utility rebate programs use this.
- The nameplate. The outdoor unit's model number lets you look up the rating later, even on a system that's already installed.
FAQ
Frequently Asked Questions
Is 16 SEER2 good?
Yes. 16 SEER2 is above both the federal minimum (13.4 to 14.3 SEER2 depending on region) and the 15.2 SEER2 ENERGY STAR level. Plenty of mini splits are rated above that; look up the exact model in the AHRI Directory.
Is SEER2 the same as SEER?
No. SEER2 comes from a tougher test that started on January 1, 2023, with higher blower static pressure. A ducted split system scores about 5% lower on SEER2 than on the old SEER. Ductless mini splits score about the same on both.
What is a good SEER2 rating for a mini split?
There's no official cutoff, but 20 SEER2 or higher is well past the 15.2 SEER2 ENERGY STAR level. Anything in that range is efficient; past about 20, getting the size right matters more than chasing another point or two.
Does SEER2 matter for heating?
Not directly. SEER2 is a cooling rating. For heating, look at HSPF2, and in cold climates check the heating capacity the unit keeps at 5°F.
How do I convert SEER to SEER2?
For ducted split systems multiply SEER by about 0.95. For ductless mini splits the factor is 1.00, so the number stays about the same. Those are the AHRI factors used by RESNET.