An air conditioner's SEER rating indicates how hard it has to work to cool your home. The higher the SEER rating of your air conditioner, the more efficient it is. Air conditioners more than 15 years old can have SEER ratings of 8 or lower, so upgrading to a standard 13 SEER unit would certainly be a good step. Keep in mind, however, that Premium air conditioners operate at up to 21 SEER, which can make a significant difference in your monthly bill. How much can you save? Click here to find out