Comparing a Central Air Conditioner and a Room Air Conditioner - Air Conditioners

Comparing a Central Air Conditioner and a Room Air Conditioner

From Kris Jensen-Van Heste, for About.com
Q: What is the difference between a central air conditioner and a room air conditioner? Which is better?

A: 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. These considerations, in hand with other factors, will determine the type of air conditioning that's best for you.

The 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 very inefficiently 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. Online charts can tell you the right BTUs for your 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.

The Central Air Conditioner

A central air conditioner cools your entire house at once using a condenser (usually located outside) and 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; for lack of that type of furnace, the cooling coils and fan will be in the attic, with ductwork coming from it to deliver the cooled air.

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 room air conditioner will cost you just a few hundred dollars, installing a central air system will run into the thousands. If you have a forced-air furnace and existing ductwork, you can expect to pay about $4,000 (more or less, depending on your region). If you don't have an appropriate furnace or ducting, you're looking at closer to $10,000.

Which Is Better?

The type of air conditioning you should choose depends on ...