When you install central air conditioning, size matters. Underestimate your cooling needs, and you could be sweating. Buy more power than you need and your living space may become cold and clammy. Any contractor you hire should calculate the size of the cooling equipment you need by using such recognized methods as the Air Conditioning Contractors of America (ACCA) Manual J. If you already have ductwork for your heating, adding a central system can cost less. But keep in mind that ducts used for heating might not be the right size or in the right location for optimal cooling.
Your contractor should use a duct-sizing method such as the ACCA Manual D. The pros should make sure that all duct sections are properly sized and that there are enough supply registers to deliver sufficient air to the right spots. Not only is the proper size ductwork essential for meeting each room's cooling needs but also because undersized ductwork can make for noisy operation. Leaky or uninsulated ducts can reduce system efficiency considerably. All joints and seams must be sealed—and not with duct tape that can dry and fall off.
If your home doesn't have ducts, adding them can be expensive. However, if you plan to cool your entire home, central air is typically the best choice. If you are not planning to cool the entire home, you might want to consider a split-ductless system. Unlike central systems, split-ductless systems need no ductwork (though they require connections for electrical, refrigerant, and condensate drains), making them easier to add to homes with designs that aren't conducive to installing ductwork.
The most and least reliable
While Consumer Reports would like to provide you with brand and model ratings of central air-conditioning systems, it would not be practical because there are so many variables to consider, including a home's size and design, and how the air-conditioning unit is installed. In fact, a significant variable affecting performance is the quality and construction of the duct distribution system. Poorly designed or installed ductwork can cause improper cooling, noise and even equipment failure. Instead, to help you make an informed choice we surveyed almost 34,000 readers who bought systems from 2007 through 2013 to find out which brands were most and least reliable central air conditioners.