SEER vs EER: AC Efficiency Ratings
Decode air conditioner efficiency numbers. Learn the difference between SEER and EER, and how to choose the right rating for your climate.
In this guide
- What SEER (and SEER2) means
- What EER (and EER2) means
- The difference between the two ratings
- Calculate cooling cost savings
- Which rating matters most for your climate
SEER measures an air conditioner's average efficiency over an entire cooling season, while EER measures its efficiency under peak, extremely hot conditions. The higher the number for either rating, the more efficient the unit.
What is SEER?
SEER (Seasonal Energy Efficiency Ratio) is the most common rating used for central air conditioners. It calculates how much cooling a system provides (in BTUs) over a typical cooling season, divided by the total electrical energy it consumes (in watt-hours).
Because the test simulates a full season, it tests the AC at various outdoor temperatures ranging from 65°F up to 104°F. This makes SEER an excellent metric for predicting average annual energy costs in temperate climates.
What is EER?
EER (Energy Efficiency Ratio) measures an air conditioner's efficiency at a single, specific operating point: an outdoor temperature of exactly 95°F. It tells you how efficiently the unit performs when it is under maximum stress.
EER is frequently used for window air conditioners and commercial equipment, and it is a critical metric for homes in extreme desert climates where the AC operates almost exclusively in 95°F+ heat.
Which rating should you look at?
Neither rating is "better"; they serve different purposes based on your geography.
- Mild/Temperate Climates: Focus on SEER. Your AC will run in mild 75°F weather just as often as 90°F weather. The seasonal average provided by SEER accurately reflects your usage.
- Extreme Desert Climates: Pay close attention to EER. If your summer stays above 95°F for months at a time, the seasonal SEER test (which includes many 70°F days) will overstate the unit's efficiency. The EER rating shows you exactly how the unit performs in brutal heat.
Calculating savings from a higher SEER
You can estimate the percentage savings when upgrading from an old, low-SEER unit to a modern, high-SEER unit using a simple ratio.
Definitions
- Old SEER: The rating of your current, aging unit (e.g., 10 SEER).
- New SEER: The rating of the replacement unit (e.g., 16 SEER).
Example
Upgrading from a 10 SEER to a 16 SEER unit: 1 - (10 ÷ 16) = 1 - 0.625 = 0.375. You will save roughly 37.5% on your cooling costs.
SEER2 and EER2
In 2023, the Department of Energy introduced updated testing procedures, resulting in the new SEER2 and EER2 labels. The new testing protocols require the equipment to operate under higher external static pressure, more accurately mimicking real-world ductwork.
Because the new test is harder, a unit that scored a 15 SEER under the old test might score a 14.3 SEER2 under the new test. It is the exact same machine with the same efficiency; only the testing ruler changed. When comparing units, always compare SEER to SEER, and SEER2 to SEER2.
For more information on our calculations, please read our Methodology and Disclaimer.