EER vs. SEER: Clarifying the Two Key Efficiency Metrics
Key Takeaways
- SEER (Seasonal Energy Efficiency Ratio) measures an AC's efficiency over an entire cooling season with varying temperatures.
- EER (Energy Efficiency Ratio) measures efficiency at a single, fixed outdoor temperature (95°F), representing peak-load performance.
- SEER is a better indicator of overall efficiency for most homeowners, as it reflects a wider range of conditions.
- EER is a very important metric for those living in extremely hot climates, as it shows how well the unit performs on the hottest days.
- Both ratings are calculated as BTUs of cooling divided by the watt-hours of energy used; a higher number is always more efficient.
When shopping for a new air conditioner, you're bombarded with acronyms. The two most important for efficiency are SEER and EER. While they sound similar, they measure two different aspects of an AC unit's performance. Understanding the distinction is crucial for choosing the right system for your climate and saving money on your energy bills.
The Definitions: EER and SEER
Both EER and SEER are ratios that measure how efficiently an air conditioner uses electricity to produce cooling. They are both calculated by dividing the cooling output (in BTUs) by the energy input (in watt-hours).
For both metrics, a higher number is always better. It means the unit produces more cooling for each watt of electricity it consumes.
- EER (Energy Efficiency Ratio): Measures efficiency at a single, specific set of conditions.
- SEER (Seasonal Energy Efficiency Ratio): Measures efficiency over a whole cooling season with a range of different temperatures.
The Key Difference: Testing Conditions
The crucial difference between the two ratings lies in the conditions under which they are tested.
EER is a snapshot of performance under a heavy, peak-load condition:
- 95°F outdoor temperature
- 80°F indoor temperature
- 50% relative humidity
SEER is a more comprehensive average. It's tested across a range of outdoor temperatures from 65°F to 104°F, simulating an entire cooling season from mild spring days to hot summer afternoons.
| Metric | What It Measures | Testing Condition | Best For |
|---|---|---|---|
| EER | Peak Load Efficiency | Fixed (95°F outdoor, 80°F indoor, 50% RH) | Hot desert climates (e.g., Phoenix) |
| SEER | Seasonal Average Efficiency | Variable (range of temps from 65°F to 104°F) | Most U.S. climates |
Which Metric Matters More for You?
The importance of EER vs. SEER depends entirely on your climate.
- For most of the country (Mixed and Cooler Climates): SEER is the more important number. Since you experience a wide range of temperatures, the seasonal average better predicts your overall annual energy costs.
- For very hot, dry climates (e.g., Arizona, Nevada): EER is arguably more important. In these regions, the air conditioner spends a huge portion of its time running at or near peak load (95°F+). The EER rating is a better indicator of how the unit will perform and how much it will cost to run during the hottest part of the summer.
The New Standards: SEER2 and EER2
As of 2023, the Department of Energy has introduced new testing standards called SEER2 and EER2. These new tests use a higher external static pressure to better simulate the resistance of a real-world duct system, providing a more accurate efficiency number.
The ratings are not directly comparable (e.g., a 14 SEER unit might be a 13.4 SEER2 unit), but the principle remains the same. When shopping for a new unit, you will see SEER2 and EER2 ratings on the yellow EnergyGuide label. Always compare SEER2 to SEER2 and EER2 to EER2.
Focus on Both When Possible
Both EER and SEER are valuable metrics. For a general estimate of annual cost, look to the SEER2 rating. If you live in a climate with extreme summer heat, pay close attention to the EER2 rating as an indicator of how the unit will hold up when you need it most. A balanced approach, considering both ratings in the context of your climate, will help you choose the most effective and efficient air conditioner for your home.