SEER2 and the M1 Test Procedure Transition

Why this matters

A contractor quoting a "14 SEER" unit in 2026 is quoting against a label that no longer exists for any product manufactured after January 1, 2023. The DOE rebuilt the entire residential central air-conditioning and heat-pump efficiency rating system effective that date. The new metrics (SEER2, EER2, HSPF2) are produced by the M1 test procedure, which uses more representative external static pressure than the old A test, with the result that the same physical unit rates approximately 4 to 5 percent lower under SEER2 than it did under SEER. A customer holding a 2018 manufacturer brochure for the same model number sees different numbers than the 2024 brochure shows, and the difference is not "they made it less efficient", it is "they measured it differently". Explaining this in 15 seconds to a customer who saw the old brochure is a real skill.

The regulatory backdrop

DOE rule 10 CFR Part 430 Subpart B Appendix M1 (the "M1 appendix") was published 2017 with an enforcement effective date of January 1, 2023 for new equipment manufactured or imported. The companion rulemaking for split-system minimum efficiency standards raised the floor:

The DOE North/Southeast/Southwest map is in 10 CFR 430.32. It splits states by climate zone for SEER2 purposes, and the southern split also imposes EER2 minimums (a peak-load efficiency metric) that the north does not. A unit can be SEER2-compliant for the north and not for the south.

SEER vs SEER2 in physical terms

SEER (the pre-2023 metric) measured cooling capacity divided by electrical input at a specific outdoor temperature schedule, with the indoor coil tested at 0.1 inches w.c. external static pressure. That static pressure was lower than typical installed residential systems actually run, which meant lab SEER ratings overstated real-world performance. M1 raised the external static pressure test condition (typically 0.5 inches w.c. for systems below 4 ton, scaling up for larger systems), which produces a more honest number.

The 4 to 5 percent typical SEER-to-SEER2 derate is the cumulative effect of:

• Higher external static (the dominant change, roughly 3 to 4 percent derate)
• Updated cycling and off-cycle assumptions (roughly 0.5 to 1 percent derate)
• Updated coil-only test rules (variable effect depending on coil match)

A nominal 16 SEER unit pre-2023 typically rates around 15.2 SEER2 post-M1, all else equal.

EER vs EER2

EER (Energy Efficiency Ratio) is the steady-state capacity divided by power at a single peak design condition (95 F outdoor, 80 F indoor return, 67 F wet bulb). EER2 uses the same definition with the M1 test procedure (higher external static), producing typically 1 to 3 percent derate.

EER2 minimums for the southern regions:

The southwest tier is stricter because peak-load grid impact is worse in hot-arid climates.

HSPF vs HSPF2 (heat pumps)

HSPF (Heating Seasonal Performance Factor) became HSPF2 under M1. The change is:

• Higher external static (matches SEER2 logic)
• Updated regional climate assumption (the test now defaults to AHRI Region IV instead of Region IV-only as the published number)
• More representative on-cycle behavior

A 9.5 HSPF unit pre-2023 typically rates around 8.1 HSPF2 post-M1. That is roughly a 15 percent numerical drop. The unit is identical; the test is more demanding.

Heat-pump minimums by region effective 2023:

Conversion factors (approximate)

For quick customer-conversation translation:

These are typical-unit averages. The AHRI directory now publishes both SEER and SEER2 for many units in their cross-reference tables, which is the authoritative source for any specific model.

Practical impact on customer conversations

Old marketing brochure vs new

A customer holding a 2021 brochure showing "16 SEER" for a model that is now listed at "15.2 SEER2" is correctly confused. The 30 second answer: "The federal government changed the test procedure in 2023 to better match how units actually run installed. The unit performs identically. The new number is calibrated to be more realistic; the old number was slightly optimistic. Your operating cost will be the same."

Federal tax credit (IRA 25C, energy-efficient home improvement credit)

The Inflation Reduction Act 25C residential energy-efficient home improvement credit, effective for property placed in service 2023 through 2032, references CEE (Consortium for Energy Efficiency) tiers that are themselves expressed in SEER2 / EER2 / HSPF2. The 30 percent credit (up to $2,000 for heat pumps, $600 for AC) requires equipment that meets or exceeds CEE highest tier as published. For 2024, that is typically SEER2 at least 16.0 and HSPF2 at least 9.0 for the bonus tier. Verify against the current CEE tier list at cee1.org because tier definitions are updated annually.

Regional minimum compliance

A southeast-zone contractor selling a 13 SEER2 unit is selling sub-code equipment. A north-zone contractor selling that same unit is compliant. Verify the home address against the DOE regional map (10 CFR 430.32) before quoting. Some manufacturers ship the same physical equipment as two different model numbers to allow proper region tagging.

Existing inventory grandfathering

References

• 10 CFR Part 430 Subpart B Appendix M1 (DOE residential central air conditioner test procedure).
• 10 CFR 430.32 (regional standards map and minimum efficiency tables).
• AHRI Standard 210/240-2023 (Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment).
• AHRI Directory of Certified Product Performance (ahridirectory.org).
• Internal Revenue Code Section 25C as amended by Inflation Reduction Act of 2022 (residential energy-efficient property credit).
• IRS Form 5695 instructions (Residential Energy Credits).
• Consortium for Energy Efficiency residential central AC and heat pump specification (cee1.org).
• DOE Federal Register notices: 87 FR 76324 (final rule, December 2022) and predecessor notices.
• Manuall internal: HVAC Efficiency Ratings Reference, HVAC Pricing Strategy.