Once upon a time, people who purchased central air conditioning systems for their homes didn’t think much about efficiency. They expected to pay a lot for cooling—and they did. Older systems were inefficient and people didn’t expect much better.
That’s changed thanks to improved technology and people in general having a greater awareness of the importance of energy efficiency, not only as a way to lower utility costs but also as a way to benefit the environment. Regular air conditioner maintenance service also plays a major role in keeping your system running at peak efficiency, ensuring you’re getting the most out of your unit’s SEER2 and EER2 ratings over time.
If you’re currently looking to purchase a new central cooling system for your home, energy efficiency will likely be on your mind. We’re experts on AC efficiency in Rochester, NY, and in this post we’ll help you better understand how energy efficiency is measured and what to look for so you can make an informed decision about your next AC. For example, understanding the differences between central AC versus ductless can help you choose a unit that aligns with your efficiency goals and home layout.
Understanding EER2 & SEER2 AC Efficiency Ratings
The two efficiency ratings you need to know about for air conditioners are EER (Energy Efficiency Ratio) and SEER (Seasonal Energy Efficiency Rating). As of 2023, these ratings have been updated to EER2 and SEER2 as part of new government initiatives to improve overall air conditioning efficiency. If you didn’t know about EER/SEER before this change, you don’t need to worry about it—basically, EER2 and SEER2 altered the scale of efficiency rating by changing the measurements used in the testing process. You only need to focus on EER2/SEER2 now.
EER2 is the ratio of the amount of cooling output from an AC (as measured in BTUs) to the amount of electricity used (as measured in watt hours) under a specific set of temperature and humidity conditions. The higher the number, the more efficient the unit. Think of EER2 as a snapshot of how the system performs.
SEER2 is the same ratio as EER2, except that the unit undergoes a series of tests with different temperature and humidity conditions to simulate an entire summer season of work. SEER2 is always higher than the EER2 of a unit. Think of SEER2 as a film of how a system performs rather than a snapshot.
In general, you’ll want to pay the most attention to SEER2, as it gives you a better understanding of how a unit will perform during a summer.
What EER2 and SEER2 Ratings Mean for Your AC
“Good” is relative here, since the higher an air conditioner scores, the more expensive the unit. Sometimes a lower efficiency unit might better suit you than a much more expensive high-efficiency one.
There is a baseline to look for: the ENERGY STAR program has new (as of January 2023) requirements for air conditioners. Standard central air conditioning systems must have SEER2 of at least 15.2 and EER2 of at least 12.0. We strongly recommend you only consider an ENERGY STAR certified air conditioner. These new requirements are good starting points for better efficiency.
There are air conditioners with SEER2 in the 20s, and if these fit your price range, you may wish to consider one. However, high efficiency ratings are not guarantees of savings. You’ll need the assistance of HVAC technicians like us to ensure you end up purchasing a unit that will work for your home. To help narrow down your choices, our guide on top-performing AC systems breaks down top-performing models based on performance and value. Efficiency won’t mean much if you’ve got an oversized/undersized unit!
Frequently Asked Questions
Question: What do the efficiency ratings EER and SEER mean for air conditioners?
Answer: EER (Energy Efficiency Ratio) measures how efficiently an AC operates at a specific set of conditions, while SEER (Seasonal Energy Efficiency Ratio) evaluates performance across an entire cooling season. The higher the number, the more efficient the system.
Question: What are the updated ratings EER2 and SEER2?
Answer: The ratings EER2 and SEER2 are updated versions introduced in 2023 that use more realistic test conditions to measure real‑world performance. They replace the older EER and SEER metrics and give a clearer idea of actual energy use.
Question: What are good target values for EER2 and SEER2 ratings when buying a central air‑conditioning system?
Answer: As of January 2023, central systems should have at least EER2 = 12.0 and SEER2 = 15.2 to meet baseline efficiency standards. Higher ratings—such as SEER2 in the 20s—are available if your budget and climate demand them.
Question: Does a higher efficiency rating always guarantee savings and better performance?
Answer: Not necessarily. While a higher rating means the unit is capable of greater efficiency under ideal conditions, real‑world savings depend on proper sizing, installation, and other system factors. A mismatched or poorly installed unit may still underperform.
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