EER vs SEER calculator

What is the difference between EER and SEER?

EER and SEER both measure how efficient an air conditioner is, but they measure it under different conditions. EER (Energy Efficiency Ratio) is a steady-state number tested at one fixed outdoor temperature, 95 degrees Fahrenheit, with the unit running at full load. SEER (Seasonal Energy Efficiency Ratio) is a seasonal average across the full cooling season, testing the unit at outdoor temperatures from 65 to 104 degrees and at partial loads. SEER is almost always higher than EER on the same unit because the seasonal mix includes a lot of mild days where the AC is more efficient.

For a typical residential split AC, SEER runs about 10 to 15 percent higher than EER. A unit rated SEER 16 usually comes in around EER 12. The new SEER2 and EER2 ratings (DOE 2023) drop both numbers by 5 to 10 percent because of the tougher M1 test, but the same relationship holds.

The EER to SEER conversion formula

AHRI (the industry certification body) publishes the standard polynomial for converting between the two. The math is:

• EER = 1.12 × SEER − 0.02 × SEER²
• SEER = (1.12 − √(1.2544 − 0.08 × EER)) ÷ 0.04

The simple rule of thumb is SEER ≈ EER × 1.12, which is close enough for shopping but off by half a point at the high end of the rating scale. The calculator above uses the precise polynomial. For most homeowners the rough rule is fine. For Manual J load calculations and state efficiency code compliance, the polynomial number is what matters.

EER to SEER conversion chart for common ratings

Quick lookup for standard residential central AC units. Convert in either direction.

• SEER 13 = EER 11.18
• SEER 14 = EER 11.76 (legacy federal minimum)
• SEER 15 = EER 12.30
• SEER 16 = EER 12.80
• SEER 17 = EER 13.26
• SEER 18 = EER 13.68
• SEER 19 = EER 14.06
• SEER 20 = EER 14.40
• SEER 22 = EER 14.96
• SEER 24 = EER 15.36

Notice that the EER curve flattens at the high end. Going from SEER 20 to SEER 24 (a 20 percent jump) only nets you about a 7 percent gain in EER. That is because higher SEER ratings come from variable-speed compressors that shine at partial load, not full load. For hot dry climates where the AC runs at peak load for hours, EER tells the more honest story than SEER.

EER2 federal minimum for the Southwest dry region

Most U.S. states only enforce SEER2 minimums on new central AC installs. The hot dry Southwest region (Arizona, California, Nevada, New Mexico) is different. There the DOE requires an EER2 floor on top of SEER2 because AC units in that climate run hard for hours at near-peak load and SEER2 alone does not catch units that fall apart under steady-state heat. The current rule for residential central AC under 45,000 BTU:

• Path A: EER2 ≥ 11.7 AND SEER2 ≥ 14.3
• Path B: EER2 ≥ 9.8 AND SEER2 ≥ 15.2 (the high-SEER alternative)

For units between 45,000 and 65,000 BTU the EER2 minimum drops slightly to 11.2 with the same SEER2 paths. If you are buying a new AC in Phoenix, Las Vegas, Tucson, Albuquerque, or anywhere south of the Sacramento line in California, both numbers have to be on the AHRI certificate.

EER vs SEER for hot climates: which one should you trust?

In Phoenix the AC runs at 95+ degrees outside for 100 days a year, often hitting 110+ in July. SEER's seasonal average is meaningless because the cooler 65-degree end of the test range almost never happens. EER is the rating that tells you how the unit performs on a real Tuesday afternoon in summer. A SEER 16 unit with EER 12.5 will outperform a SEER 18 unit with EER 11 in extreme heat, even though the second unit has the higher SEER on paper.

Cold climates flip the math. In Boston or Minneapolis the AC runs maybe 700 hours a year, most of them at mild outdoor temperatures where SEER excels. EER barely matters because the unit almost never hits 95-degree steady-state conditions. In those climates buy on SEER2 and ignore EER. In hot dry climates buy on EER2 and use SEER2 as the secondary check.

Why high SEER does not always mean high EER

SEER rewards variable-speed and two-stage compressors that throttle down on mild days. A Carrier Infinity 24 SEER2 variable-speed unit hits SEER2 by running at 25 percent capacity most of the season. But on a 110-degree day in Phoenix it has to run flat out, and its EER drops to the same range as a much cheaper single-stage unit. This is why two AC units with the same SEER2 rating can have EER2 numbers that differ by 1 to 2 full points.

Goodman, Rheem, and base Carrier single-stage units tend to have higher EER per dollar spent. Premium variable-speed units from Trane, Lennox, and Carrier Infinity tend to have higher SEER per dollar but only marginally higher EER. In the Southwest dry region the Goodman and base Rheem units are often the better buy for that reason.

How EER and SEER affect your power bill

For shopping purposes, SEER2 is the right number to compare across the country because your real-world bill tracks closer to SEER than to EER in most climates. The exception is the Southwest dry region, where EER2 is the better predictor. Rule of thumb in a typical mixed climate at 1,100 cooling hours and $0.18 per kWh: every 1.0 point increase in SEER2 saves about $25 to $40 per year per ton of AC. In a hot dry climate at 2,000 cooling hours, every 1.0 point increase in EER2 saves about $35 to $60 per year per ton. Use this calculator to convert between ratings and our SEER2 savings calculator to model annual bill impact.