This report focuses primarily on central air conditioner units. For some homes, other whole-home systems are more appropriate. This is especially true if your home has no existing ductwork.
In a regular central air conditioner, the evaporator, condenser and compressor are housed in a single unit. A large, roughly cube-shaped box is usually installed next to a home on a concrete slab, or on the roof. The unit is connected to ducts that run throughout the home. If the home has forced-air heating, both systems use the same ductwork.
A split system is cheaper to install. In a split AC system, the evaporator and blower are in a separate unit which lives inside the home. Split systems are reported to be quieter than single-box air conditioners. They require regular cleaning, and the system still requires ductwork.
If your home doesn't have ductwork, a ductless mini-split AC system may be cost-effective. In this type of system, each room or home area has its own air-handling unit. This gives you the ability to adjust climate control for each room. ACEEE says ductless mini-split systems are much more expensive unless you need to install ductwork for a conventional single-box system.
Contractors are not partial to ductless systems, but they will recommend them for homes where it's impossible to install ductwork. If you're in that situation, see our reports on window air conditioners or portable air conditioners, which may make more sense.
ACEEE says that evaporative coolers (also known as swamp coolers) may make sense in dry climates, such as the Southwest. One type of evaporative cooler adds moisture to a home. These units use vapor compression to cool. The city of Phoenix says evaporative coolers use more water and electricity than they should, but in a very old paper, The University of Arizona says they use "one-third of the energy of refrigerated air-conditioning." The U.S. Department of Energy covers some of the trade-offs between evaporative coolers and central air conditioners in its report called "Evaporative Coolers."