EER2 (Energy Efficiency Ratio 2) measures your air conditioner's cooling efficiency at a single, fixed peak condition: 95 degrees F outdoor, 80 degrees F indoor, 50% humidity. Unlike SEER2 which averages over a whole season, EER2 tells you how efficient the unit is on the hottest days when it's working hardest. A typical central AC ranges from 10 to 14 EER2, with higher numbers meaning less electricity per BTU of cooling.
EER2 replaced the old EER on January 1, 2023, alongside the SEER-to-SEER2 transition. If you live in a hot climate where your AC runs at full capacity for weeks, EER2 is arguably more relevant than SEER2 for predicting peak-month bills.
The EER2 Formula
EER2 = Cooling Output (BTU/h) / Electrical Input (W)
At the 95 degrees F test condition, the system runs at full capacity. Cooling output in BTU per hour is divided by total electrical input in watts. An EER2 of 12 means 12 BTU of cooling per watt-hour at peak conditions.
To convert to COP: COP = EER2 / 3.412. An EER2 of 12 equals COP 3.52.
EER2 vs EER: What Changed
| Feature | EER (Old) | EER2 (New) |
|---|---|---|
| Effective Date | Before January 2023 | January 2023 onwards |
| Test Procedure | Original low static pressure | M1 with 0.5 in. w.c. |
| Test Conditions | 95F outdoor, 80F indoor, 50% RH | Same conditions |
| Rating Drop | Baseline | About 4.7% lower |
| Conversion | Baseline | EER2 = EER / 1.047 approx |
The test conditions are identical. The only change is external static pressure, making the blower work harder and lowering the number slightly.
EER2 vs SEER2: Different Purposes
| Aspect | SEER2 | EER2 |
|---|---|---|
| Measures | Seasonal average efficiency | Peak-condition efficiency |
| Temp Range | 65-104F weighted average | Fixed at 95F |
| Operating Mode | Mix of part and full load | Full capacity only |
| Favors | Variable-speed units | Strong full-load performers |
| Best For | Annual cost estimates | Peak-month cost estimates |
| Typical Range | 13.4-26+ | 10-14 |
A system with 22 SEER2 but only 11 EER2 achieves its high seasonal rating through part-load efficiency. On a 100 degree F day at full blast, it's delivering only 11 EER2. A different system at 17 SEER2 / 13 EER2 is less impressive seasonally but uses less electricity on the hottest days.
For hot climates (Phoenix, Houston, Miami), pay attention to EER2. When your AC runs full capacity 8-12 hours daily in peak summer, EER2 better predicts your July/August bill than SEER2. Aim for 12+ EER2.
Current EER2 Minimums
| Standard | Split AC EER2 | Split HP EER2 | Notes |
|---|---|---|---|
| Federal Min (South/SW) | 11.7 | 11.7 | Required in South/SW regions |
| Federal Min (North) | No separate min | No separate min | North doesn't specify EER2 for ACs |
| ENERGY STAR | 12.0+ | 12.0+ | Part of certification |
| 25C Tax Credit (AC) | 12.0+ | 12.0+ | Required with 17.5 SEER2 |
| 25C Tax Credit (HP) | 12.0+ | 12.0+ | Required with 16 SEER2 and 9.0 HSPF2 |
Pre-expiration 25C credit required BOTH SEER2 AND EER2 minimums. Through Dec 31, 2025, the $600 federal 25C AC credit required 17.5 SEER2 AND 12.0 EER2 — a unit meeting one but not the other didn't qualify. The 25C credit expired for installs after Dec 31, 2025 under the OBBBA (PL 119-21, signed July 4, 2025); the dual-threshold criteria remain a useful efficiency target since most state/utility rebates and IRA HOMES use the same or similar tests.
EER2 by Compressor Type
| Compressor Type | Typical EER2 | SEER2 Range | SEER2/EER2 Ratio |
|---|---|---|---|
| Single-Stage | 10.5-12.5 | 13.4-16 | 1.27-1.28 |
| Two-Stage | 11.0-12.5 | 16-19 | 1.45-1.52 |
| Variable-Speed | 11.5-14.0 | 18-26+ | 1.56-1.86 |
Variable-speed systems have the widest SEER2-to-EER2 gap. Their seasonal ratings are stellar due to part-load efficiency, but full-load EER2 is only modestly better than two-stage units.
When EER2 Matters More Than SEER2
Extreme heat climates. In Phoenix where highs exceed 110 degrees F for weeks, your AC runs near full capacity for extended periods. EER2 better predicts July electricity costs.
Demand-charge rates. Some utilities charge based on peak demand (kW). High EER2 means fewer watts drawn at peak, reducing demand charges.
Commercial applications. Commercial systems are often evaluated on EER or IEER because they frequently operate at full capacity during business hours.
Peak-Day Cost Calculation
Peak-Day Cost = (Capacity BTU/h / EER2) x Hours x ($/kWh / 1,000)
For a 3-ton (36,000 BTU/h) AC at 12 EER2 running 14 hours on a 100 degree day at $0.16/kWh:
36,000 / 12 = 3,000 W = 3.0 kW. Then 3.0 kW x 14 hours = 42 kWh x $0.16 = $6.72 per day.
At 10 EER2: 3,600 W = 50.4 kWh = $8.06 per day. Over 60 peak days, that's $80 difference.
Top EER2 Units by Brand (2026)
| Brand | Model | EER2 | SEER2 | Type |
|---|---|---|---|---|
| Lennox | XC25* | 13.5 | up to 26 | Variable-speed |
| Carrier | Infinity 24 | 13.0 | 24 | Variable-speed |
| Daikin | DX20VC | 13.0 | 20 | Variable-speed |
| Trane | XV20i | 12.5 | 22 | Variable-speed |
| Rheem | RA20 | 12.5 | 20 | Variable-speed |
| Goodman | GVXC20 | 12.5 | 20 | Variable-speed |
| York | YXV | 12.0 | 20 | Variable-speed |
Lennox XC25: marketed at "up to 26". Sources conflict on whether that figure is SEER (legacy 2018 metric) or SEER2 (2023 M1 procedure). Central-AC certified ratings are match-dependent — the AHRI figure varies with the specific indoor/outdoor combination. Verify the exact rating for your quoted match at the AHRI Directory. Lennox now also markets the SL25KCV/SL28XCV as the current variable-capacity flagship. (Source: lennox.com.)
Key Takeaways
- EER2 measures efficiency at 95 degrees F — performance on the hottest days
- EER2 replaced EER on January 1, 2023 using the M1 test. Numbers are roughly 4.7% lower.
- SEER2 is always higher than EER2 for the same unit due to favorable part-load averages
- Variable-speed units have the widest SEER2-to-EER2 gap — great seasonal averages, moderate peak performance
- A 2-point EER2 gap costs ~$80 over 60 peak days — a 3-ton unit at 10 vs 12 EER2 running 14 hours at $0.16/kWh (see Peak-Day Cost section)
- Federal tax credit requires 12.0 EER2 alongside 17.5 SEER2 for ACs
- Convert EER2 to COP: divide by 3.412
Frequently Asked Questions
SEER2 includes performance at mild outdoor temperatures (65-85F) where the system runs at partial capacity with very high efficiency. EER2 is measured only at 95F where the system runs at full capacity and works hardest. The mild-weather partial-load efficiency raises the SEER2 seasonal average above the EER2 peak-load number.
Sources & References
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