In the HVAC world, SEER and EER are two of the most frequently referenced efficiency ratings. They tell you how much cooling you get for the energy you pay for—but the path to these ratings hasn’t always been clear. Before 1975, there was no universal standard for rating cooling efficiency. That changed when industry groups and federal regulations stepped in.
Let’s break down what each rating means, why both are important, and how they affect real-world performance and costs.
EER — The Original Efficiency Rating
In 1975, the Air Conditioning & Refrigeration Institute (ARI) introduced the Energy Efficiency Ratio (EER).
What EER Measures
EER is a steady-state efficiency measurement:
BTU/hr of cooling output ÷ Watts of electrical input
But here’s the key:
EER is measured at specific laboratory conditions:
- Indoor: 80°F dry bulb / 67°F wet bulb
- Outdoor: 95°F dry bulb / 75°F wet bulb
It was originally designed to mirror the “steady-state” approach used for gas furnaces, but it did not account for real-world operating patterns, cycling losses, or seasonal temperature variations.
Different climates = different performance outcomes
• A 10 EER system in Florida doesn’t perform the same as a 10 EER system in Arizona, even though conditions are both “hot.”
Why SEER Was Created
In 1978, Congress passed legislation requiring residential HVAC equipment under 65,000 BTU/hr to be labeled with a more realistic efficiency rating that considers seasonal conditions. Thus:
Seasonal Energy Efficiency Ratio (SEER)
SEER measures total cooling output over an entire cooling season divided by total electricity consumed during that season:
Total BTUs over the season ÷ W