Window units that block the sun from your room, buzz, and shake violently every time the condenser switches on are basically begging for attention—very few consumers walk out the door without remembering to shut off their window units. The quiet and unobtrusive functioning of central air conditioners, on the other hand, can lead to accidental overuse. Industry observers note that people tend to set their central air conditioner to a comfortable temperature and never change it.
Window units also offer room-by-room control. For singletons or couples who occupy only one bedroom at night, cooling a single room consumes a small fraction of the energy that a central air conditioner would.
Central air units are getting smarter, though, and accordingly more efficient. Programmable thermostats can make up for forgetful central A/C users by shutting the unit off when no one is home. Some central air systems even divide homes into separately controlled zones, so you don't have to cool the kitchen at 3 a.m. just to keep your bedroom a sleepable temperature. And some new central air conditioners have an air handler in each room, skipping the ducts entirely, combining precise control with improved efficiency and less noise.
Because of the construction and behavioral variables, it's impossible to pronounce a winner in this particular competition. As is often the case, the choice is often going to come down to each consumer's behavior. Generally speaking, the newfangled ductless system is going to be the most efficient but priciest option upfront. If you're choosing between an old-school central air system and window units, the latter could be better if you're childless, live in a large home in a dry environment, or tend to be forgetful about adjusting your thermostat.
The Lantern thanks Jennifer Amann of the American Council for an Energy-Efficient Economy.
Click here to see a slide show of clever and humorous cooling systems.