GuideViews

It is critical that you get an air conditioner that is sized correctly.  Coling capacity is generally rated according to BTU or tons.  BTU is a measure of how much heat can be removed.  1 ton is equal to 12,000 BTU/hour of cooling.  As a general rule you want about 1 ton or 12,000 BTU/hour for 500 sq ft of living space that you want to cool. 

SEER (seasonal energy efficiency rating) is a measure of the efficiency rating of your air conditioner.  In 1992 10 SEER was the minimum rating and it was increased to 13 SEER for units made after 1996.  A 13 SEER unit is about 30% more efficient than a 10 SEER unit for comparison.  The higher the SEER the better and typically higher SEER units like 14 or 15 will cost more but save you on monthly energy bills.

Noise from an air conditioner can be a major nuisance.  The sound rating is measured in SRN (sound rating numbers).  Sound from air conditoners is measured in bels from 0 to 13 (loudest).  Anything lower than 7 bels is considered very quiet.