EER stands for Energy Efficiency Ratio, an objective measurement of the AC unit's efficiency. This is determined by three parameters during testing:
1. A set outdoor temperature of 95° F
2. A set indoor temperature of 80°
3. A relative humidity level of 50%,
SEER stands for Seasonal Energy Efficiency Ratio. Like EER, it is a measurement of an AC unit's efficiency. However, as its name suggests, the SEER measures the unit's efficiency over the course of an entire cooling season.
This is done by measuring the average EER over a range of indoor and outdoor temperatures, and across varying humidity levels, to simulate the run of an entire season. The higher the SEER rating, the more efficient the unit i