Ask about the contractor's experience. When getting bids, make sure the contractor uses a recognized method, such as the Air Conditioning Contractors of America's Residential Load Calculation Manual, also called Manual J, to determine the required cooling capacity you need. Manual D often is used for assessing ductwork needs. Ask for a printout of all calculations and assumptions, including the ductwork design. Be leery of contractors who base estimates merely on house size or vague rules of thumb.
Brands play an important role in a unit's efficiency.
Consumer Reports notes that, in its reader surveys, American Standard, Ruud and Trane are among the more reliable brands recommended. Keep in mind, though, that improper installation can make even the best system run poorly. Air conditioning units with a SEER rating of 11 to 14 tend to hold up best, according to the study. A system with a SEER of more than 14 tends to be more complex, with more that can go wrong. Another thing to consider when replacing a unit or installing a new one is matching new equipment with old.