Walk into any equipment quote since 2023 and the numbers look familiar but slightly off: SEER became SEER2, EER became EER2, and HSPF became HSPF2. The switch came from a new federal test procedure that took effect January 1, 2023, and the U.S. Department of Energy is blunt that "they are not directly comparable" to the old metrics ([DOE](https://www1.eere.energy.gov/buildings/appliance_standards/pdfs/2023_CAC_Standards_FAQ_10-5-2022_Final.pdf)). Here's what actually changed and how to read it.
Why the "2" — a tougher test, not a different machine
The "2" doesn't mark new equipment. It marks a new test procedure, codified in 10 CFR Part 430, Appendix M1, which AHRI Standard 210/240-2023 uses to rate residential central air conditioners and heat pumps ([AHRI](https://www.ahrinet.org/system/files/2024-09/AHRI%20Standard%20210.240-2023%20(2020)%20ICS.pdf)). The biggest practical change: conventional ducted systems are now tested at a minimum external static pressure of 0.50 in. of water column (w.c.), reflecting real-world duct resistance, where the older test ran at lower pressure ([ENERGY STAR](https://www.energystar.gov/sites/default/files/ENERGY%20STAR%20Version%206.1%20Central%20Air%20Conditioner%20and%20Heat%20Pump%20Final%20Specification%20(Rev.%20January%20%202022).pdf)).
Because the equipment works harder against that resistance in the test cell, the same unit tends to post a lower number under SEER2 than it did under SEER. ENERGY STAR's specification-development materials pair 14.0 SEER with 13.4 SEER2 and 16.0 SEER with 15.2 SEER2 as approximate equivalents ([ENERGY STAR](https://www.energystar.gov/sites/default/files/asset/document/ENERGY%20STAR%20Version%206.0%20Central%20Air%20Conditioner%20and%20Heat%20Pump%20Final%20Data%20Package_0.xlsx)) — but again, DOE stresses the two are not directly comparable.
Don't compare SEER to SEER2 across years.A 14 SEER unit from 2022 and a 14 SEER2 unit from 2024 are not the same animal — the test changed. When comparing quotes, line up SEER2 against SEER2 only.
The federal minimums (and why your region matters)
Since January 1, 2023, the nationwide floor for a split-system AC is 13.4 SEER2 and for a split-system heat pump 14.3 SEER2 / 7.5 HSPF2 ([DOE](https://www1.eere.energy.gov/buildings/appliance_standards/pdfs/2023_CAC_Standards_FAQ_10-5-2022_Final.pdf)). But split-system and single-package ACs also carry regional requirements: the Southeast and Southwest get a higher 14.3 SEER2 minimum (13.8 for units rated at 45,000 Btu/h or more), and the Southwest adds EER2 peak-efficiency requirements. The "North" region is defined as states with 5,000 or more heating degree days ([DOE](https://www1.eere.energy.gov/buildings/appliance_standards/pdfs/2023_CAC_Standards_FAQ_10-5-2022_Final.pdf)).
| Equipment | North | Southeast | Southwest |
|---|---|---|---|
| Split AC <45,000 Btu/h | 13.4 SEER2 | 14.3 SEER2 | 14.3 SEER2 (+ EER2) |
| Split AC ≥45,000 Btu/h | 13.4 SEER2 | 13.8 SEER2 | 13.8 SEER2 (+ EER2) |
| Split heat pump | 14.3 SEER2 / 7.5 HSPF2 (nationwide) | ||
| ENERGY STAR heat pump (certified) | 15.2 SEER2 / 7.8 HSPF2 | ||
The 2026 news: ENERGY STAR dropped central ACs
Here's the current wrinkle. Effective February 1, 2026, the EPA removed residential central air conditioners from the ENERGY STAR central AC / heat-pump specification; air-source heat pumps remain covered, including a dedicated cold-climate tier ([ENERGY STAR](https://www.energystar.gov/sites/default/files/2025-12/ENERGYSTARInformationtoAssistEEProgramPlanningDec2025.pdf)). Practically, a new central AC won't carry the ENERGY STAR mark anymore — but a heat pump will, at SEER2 ≥ 15.2 ([ENERGY STAR](https://www.energystar.gov/sites/default/files/2025-04/ENERGY%20STAR%20Version%206.2%20Heat%20Pump%20Specification%20Rev.%20March%202025.pdf)). That lines up with where residential HVAC is heading: one electrified unit that heats and cools.
Rated efficiency is a ceiling, not a guarantee.The SEER2 number is what a matched system achieved in a test cell. Duct leakage, refrigerant charge, and airflow decide what actually shows up on your bill — that's where most efficiency is lost or preserved in the field.
How to actually use these numbers
- Read the yellow EnergyGuide label. It lists the SEER2 (and HSPF2 for heat pumps) with a range bar against similar models. Fastest single spec check on any quote.
- Get the AHRI Reference Number. For a split system, the rated efficiency only holds for a certified matched indoor/outdoor combination. Ask for the AHRI Certificate of Product Ratings and verify it in the AHRI Directory of Certified Product Performance ([AHRI](https://www.ahrinet.org/certification/cee-directory/air-conditioning-and-heat-pump-efficiency-101)). The wrong coil can drop a system below its rated SEER2.
- Installed ≠ rated. A 15.2 SEER2 system on leaky, undersized ducts can deliver like a 13. A proper load calculation (Manual J) and decent duct condition matter as much as the sticker number.
The bottom line
SEER2 is the new common currency for AC and heat-pump efficiency. Read it only against other SEER2 numbers, mind your region's minimum, verify the AHRI matched-system certificate, and remember that installed efficiency — not the test-cell rating — is what reaches your utility bill.
HVAC Zone Inc is a multi-brand dealer; this article is brand-neutral and names no product as "best." This content is educational and not a substitute for a site-specific assessment by a licensed professional. Want a load calculation and an efficiency comparison tailored to your home? Request a consultation — we'll size it to the actual building, not the brochure.