What SEER rating should I look for in a new AC system?

SEER (Seasonal Energy Efficiency Ratio) measures cooling efficiency — higher is better. The federal minimum for new systems in the Midwest is now 14 SEER2 (a revised testing standard).

Most quality mid-range systems run 16–18 SEER2; high-efficiency units reach 20+ SEER2. The payback on a higher-SEER unit depends on how much you run your AC — in Illinois's climate with moderate cooling seasons, a 16–18 SEER2 unit typically hits the right balance of upfront cost and energy savings.