Remember: Bigger doesn’t always mean better. Oversized equipment can cause reduced comfort and excessive noise. Oversizing can also shorten the life of the equipment by causing it to cycle on and off more frequently than a properly sized unit. Too large a unit will not adequately remove humidity.
However, undersized equipment can reduce the efficiency and accelerate wear on system components, leading to early failure. Too small a unit will not be able to attain a comfortable temperature on the hottest days.
When buying an air conditioner, look for a model with a high efficiency. Central air conditioners are rated according to their seasonal energy efficiency ratio (SEER). SEER indicates the relative amount of energy needed to provide a specific cooling output. Many older systems have SEER ratings of 6 or less. The minimum SEER allowed today is 13. Look for the ENERGY STAR® label for central air conditioners with SEER ratings of 13 or greater, but consider using air conditioning equipment with higher SEER ratings for greater savings.