What to Look for
Room air conditioners are rated by the number of BTUs, or British thermal units, of heat that they can remove per hour. Contrary to what you might think, it doesn’t make sense to run out and buy the most powerful unit you can find. You could wind up spending much more than you need to. Upgrading to the highest efficiency you can afford, however, is a good investment. In very hot climates you need an efficiency rating of 10, but 9 will do in milder climates.
How Many BTUs?
To calculate the number of BTUs you need, measure the room you’re cooling and multiply by 35. A room that is 12 x 12, or 144 square feet, for instance, needs a unit with a capacity of around 5,000 BTUs to keep it cool. If you’ve got a shady window to install the unit, you can lower that number by 10 percent. For a sunny window, add 10 percent. If it’s in the kitchen, add 4,000 BTUs. And if it’s a room used by more than two people during cooling hours, add 600 BTUs per person.
Plugging in Your Air Conditioner
Most room air conditioners can be plugged into a standard 110V 15- or 20-amp circuit as long as it’s not shared with any other major appliance. Larger 7.5-amp units need their own dedicated circuit.
Sealing Your Window
Make sure to measure the window you’re installing in before you buy. While it should come with expandable filler panels, you’ll need weather stripping and tape to seal the unit to the window and keep heat from leaking in. Have some spare lumber and screws handy in case you need to build up the window frame or sill to accommodate the unit.
Getting Help with Installation
Most importantly, have a friend help you. Even small air conditioners are heavier than they look and you don’t want to drop the unit out the window.