When looking at cooling system for your house your two basic choices are room air conditioners and central cooling systems. While the central units work via one unit pumping cool air through duct work to all the rooms of your house, a single room conditioner resides only in the location that it is cooling.
There are many kinds of room air conditioners but the basics are window units and portable units. The window and portable air conditioners work great if you are on a budget or only have need to cool one or two rooms at any given time. The other good thing about room systems is that you do not waste money or power cooling rooms that are not in use like you would with a central conditioning unit.
The difference between window and portable room air conditioners is that while you can move the portable from room to room, the window system is pretty much stuck where you install it. Here is an interesting point about the power of your room conditioning system. If you are getting stuck between getting a large or small air conditioner because of energy consumption concerns here is a tip. A small room conditioner burns less energy running longer to cool a room than a powerful larger air conditioner running for a short period of time to cool the same room. So size is a matter of how quickly you want the room cooled.
Another feature that most room air conditioners have these days is timers. These are a great option to look for because instead of paying to keep a room cool all day, you can set a timer to turn on the air conditioner just before you will be home.
Besides portability the largest factor in choosing an air conditioner for your room will be the size of that room. When picking out your cooling system you will match your air conditioner to the room by the square footage of that room. Length by width. So a room 12 feet wide by 8 feet long is 96 square feet. You must now choose the room air conditioner that has enough power to efficiently handle that much square footage. Overkill is not a good thing as it will cost you on the power bill in the long run.