When deciding between installing a central air conditioning system or buying a unit that fits in the window of one room, the two most important things to consider are the size of the area you want to cool and dehumidify and the size of your budget.
Here are some of the pros and cons of both kinds of air conditioners.
Room Air Conditioner
A room air conditioner most commonly fits into a window, though there are models that can be installed into an exterior wall. It's called a room unit because it really can't cool much more than that. Whether mounted in a window or wall, this type of air conditioner plugs into a standard electrical outlet and doesn't need special wiring. A larger wall unit requires its own circuit, however, and thus entails hiring an electrician as well as a contractor or handyman for the installation.
A room air conditioner pulls hot air in from the outside and cools it with a fairly complicated process that involves a refrigerant gas, compression, heat absorption, condensation, coils and a fan that blows the cooled air into the room.
It's essential to determine the size of the area you want to cool: If you buy too small a unit, it will keep running, increasing your utility bills without making you feel much cooler. If the unit is too large for the space, it will cool but with humidity build-up, leaving you feeling cold and clammy.
The air conditioner's power is measured in British thermal units. The more BTUs, the higher the price. The smallest units are typically 5,000 BTUs, while the biggest are around 20,000 BTUs. A 5,000-BTU unit won't cool more than about 150 square feet, or a 10-by-15-foot room. A 20,000 BTU unit will handle more than 1,100 square feet.
To get the right size, calculate the area of your room (length times width), adding 10 percent for very high ceilings or a particularly sunny room.
Some features you may want to consider include a thermostat built into the fan; an integrated timer so the unit can turn on before you get home from work; and an easily accessible filter for frequent cleaning.
Central Air Conditioner
A central air conditioner cools your entire house at once using a condenser (usually located outside), a fan-and-coil system and ductwork that brings the cooled air to each room and returns the air for cooling again. It usually works in tandem with a forced-air furnace and its related ducting.
Similar to the window unit, the central unit's strength is measured in BTUs per hour, but you'll sometimes encounter the term "tonnage." A contractor should calculate your home's specific heat gain based on insulation; the number, type and exposure of windows and doors; how the sun hits your house; and other factors.
While a small room air conditioner can be had for under $200, installing a central air system can run into the thousands, depending on the size of your house and whether you have a forced-air furnace and the right kind of existing duct work.
Central Air Vs. Room Air Conditioners
The type of air conditioning you should choose depends on your situation. If you're renting or want to cool only one room to sleep in, for example, the window unit is your best bet. If your budget is limited and you can't afford a central system, a combination of window units placed in several different rooms may work for you.
On the other hand, if you own your home and have a forced-air furnace and ductwork, but you're sweating through the summer or coordinating window units, taking the central-air plunge might be the way to go. Once installed, central units are virtually maintenance-free, quiet and effective, and in the long run, they can save you money.
Programmable thermostats can also help you save on utility bills by cooling the house just before you get home or raising the temperature a few degrees during the day or night according to your preferences.