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 ÷ Watt-hours over the season
SEER is based on AHRI 210/240 test procedure and includes:
- Variable outdoor conditions
- Cycling on/off patterns
- Startup losses
- Part-load performance
Where EER represents “highway MPG,” SEER is more like “city MPG”—it better reflects how systems operate day-to-day in a home.
A Quick Historical Snapshot
|
Year/Period |
Typical Efficiency |
Notes |
|
1974 |
6 EER |
Industry norm at the time |
|
Mid 1980s |
8 SEER |
First generation SEER-rated units |
|
1992 |
10 SEER minimum |
First federal mandate |
|
1993 |
9.7 SEER for packaged units |
Slightly different requirement |
|
2015 |
Regional SEER requirements introduced |
13–14 SEER depending on region |
Current SEER Standards
As of January 1, 2015:
- Most regions must meet 14 SEER
- Northern region is allowed to continue selling 13 SEER for certain applications during a grace period
Heat Pumps
The big shift:
Nationwide heat pump standards increased to:
- 14 SEER
- 8.2 HSPF
HSPF — Heating Efficiency for Heat Pumps
Since heat pumps provide heating and cooling, they also have a heating efficiency rating:
Heating Seasonal Performance Factor (HSPF)
= Total BTUs of heat delivered ÷ Watt-hours consumed
Again: higher number = higher efficiency
So Which Rating Matters: SEER or EER?
Both are useful—but for different reasons.
EER
- Single-point rating
- Measured at high outdoor temperature
- Good indicator of performance during peak summer heat
- Often used in commercial specs
SEER
- Seasonal rating
- Best for comparing residential equipment
- Reflects part-load efficiency, cycling losses, real-world use
Emerging Efficiency Metrics
As HVAC technology evolves—especially with ERVs, VRFs, and data center cooling—new rating systems have been introduced:
- CEF (Combined Efficiency Factor)
Incorporates ERV contribution
- IEER (Integrated Energy Efficiency Ratio)
A seasonal metric for commercial rooftop A/Cs
- SCHE (Simultaneous Cooling & Heating Efficiency)
Used in heat recovery VRF systems
- SCOP (Sensible Coefficient of Performance)
Sensible cooling efficiency based on ASHRAE Standard 127
These reflect more complex systems and integrated designs.
Bottom Line
- EER = peak performance rating
- SEER = seasonal average performance rating
- Higher ratings lower operating costs
- Modern standards improve energy savings for homeowners and commercial facilities alike
