This is a side by side comparison of condensing units installed on new construction. The unit on the left is a 12 SEER, and the unit on the right is a newly required 13 SEER. Both are 2-ton units. Notice the size differences. According to a manufacturer’s bulletin, the difference in efficiency between the 12 & 13 SEER units is 9%. As remainding stocks of 12 SEER units are depleted, we will see more of the larger and more efficient 13 SEER units.