SEER vs SEER2: What Changed and Why It Matters in 2026

SEER2 replaced SEER as the official US efficiency standard for air conditioners and heat pumps on January 1, 2023. If you are comparing equipment from before and after 2023, or trying to understand why two units with different SEER ratings feel comparable, this guide explains exactly what changed, how to convert between the two ratings, and what efficiency number to look for when buying in 2026.

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What Is SEER?

SEER (Seasonal Energy Efficiency Ratio) measures cooling efficiency as BTU of cooling delivered per watt-hour of electricity consumed, averaged across a full cooling season. A SEER of 18 means the system delivers 18 BTU of cooling for every watt-hour of electricity — on average across the season.

What Changed with SEER2?

The US Department of Energy updated the test procedure in 2023 to use a higher external static pressure (0.5 inches of water column vs 0.1 previously). This better reflects real-world duct resistance in installed systems. The result: most products tested under SEER2 score approximately 5% lower than their SEER rating — not because they got less efficient, but because the test is more demanding.

Quick conversion: Multiply SEER by 0.95 to get the approximate SEER2 equivalent. Divide SEER2 by 0.95 to convert back.

New Minimum Efficiency Standards (2023 Onward)

What SEER2 to Look for When Buying in 2026

• Minimum (code compliance): 13.4–14.3 SEER2 depending on region
• Good efficiency: 17–20 SEER2 — meaningful energy savings over minimum
• High efficiency: 20–24 SEER2 — premium tier; qualifies for maximum rebates
• Best available: 24–42 SEER2 — available on top-tier Mitsubishi and Carrier models

For IRA Section 25C tax credit eligibility in 2026, split-system heat pumps must meet a minimum efficiency threshold set by the Consortium for Energy Efficiency (CEE) Tier 1 criteria — currently 15.2 SEER2 / 8.1 HSPF2. Always verify the current threshold at energystar.gov before purchasing.

Frequently Asked Questions

Does Canada use SEER2?

No — Canada continues to use the original SEER rating system, not SEER2. When comparing Canadian and US product specifications, account for the ~5% difference: a Canadian unit rated at SEER 20 is approximately equivalent to a US unit rated at SEER2 19.

Is SEER2 only for cooling, or does it affect heating ratings too?

SEER2 applies to cooling efficiency. The heating efficiency rating also changed — HSPF (Heating Seasonal Performance Factor) was updated to HSPF2 using the same revised test procedure, resulting in similar ~5% reductions in ratings. Both SEER2 and HSPF2 are now the standard for US equipment sold after January 2023.

Related reading:
→ Mini-Split HSPF Rating: What It Means for Heating Costs
→ What to Look for When Buying a Mini-Split: 10 Key Factors
→ Mini-Split Rebates Canada 2026: Federal + Provincial Guide