Department of Energy released new measurement & performance parameters with HVAC equipment and is denoted as SEER2 vs SEER for energy efficiency. Due to the extreme measurement standards used the SEER2 rating is or would be on average 4.3% higher if calculated on the older SEER standards. So an older model at 14 SEER if measured on the old metrics would be 18.3 SEER. SO you will see a lower SEER2 rating due to this as its a totally new and more accurate calculation. Click the link for more information & understanding