Do you need help choosing a new central air conditioner? Central air conditioners each have a SEER rating, which stands for seasonal energy efficiency ratio. This number reflects how much energy it takes for the air conditioner to provide a specific cooling output. If you are buying a new air conditioner, this is an important number to keep in mind because this rating is directly related to how much you will spend on your monthly energy bills. The minimum SEER allowed today is 13, but you can get units with a SEER of over 20 if you are looking for the most energy efficient unit possible.