Measure the Room
Measure the room, length times width, to determine what Btu requirements you need to adequately keep it cool. There are standardized cooling requirements that conform to room size. For example, a 10-by-15-foot, or a 150-square-foot room, only needs an air conditioner with 5000 Btu of cooling power, while an 18-by-25-foot room needs a 10,000 Btu air conditioner to keep the room cool. These are the minimum requirements for adequate room cooling.
Measure the Window Size
Measure the window size to determine if a window air conditioner will fit. Most window units fit double-hung windows. They have adjustable side accordion pull-out panels that bridge the gap from side to side. However, mini compact air conditioners are made that fit into virtually any smaller-size window. They cost more than a standard size unit, but they cool just as effectively.
Environmental factors include a room located on a sunny side or shaded side of the house. How many people use the room on a regular basis must be taken into account. For example, if the room receives full sun during the day, add another 500 to 1000 Btu of cooling power. A shaded room allows you to decrease the Btu requirements by 10 percent. Add an extra 600 Btu of cooling power for each person who occupies the room on a regular basis.
Portable Air Conditioners
A portable air conditioner connects to a window through a hose. The units are mounted on wheels and easily travel from room to room where needed. Even the smallest window accommodates a portable air conditioner hose. If your window is too small, not high enough, or if you are not able to open it more than a few inches, a portable unit allows cooling power and vent through a 6- or 8-inch window opening.