The most important parameter, which should be considered when choosing an air conditioner, is the area of the room. The more it is, the more powerful conditioner should be. If its power will be not enough, conditioner simply will not cope with cooling, especially in hot weather. And if it is too powerful, the power consumption will be unreasonably high. Moreover conditioner will switch off and switch on very often, as the necessary temperature in a small room is reached quickly. And constant switching will accelerate its wear and tear.
That is why for small rooms and offices it is better to choose conditioners with lesser capacity, and for large halls of houses and big offices - more powerful models. On average about 2,5 kilowatt of power is necessary for cooling of 25 cubic meters of premise (or 1 kilowatt of power for cooling of each 10 square meters for rooms with 2,5 m ceiling). If the room has powerful heaters or there are usually a lot of people in it, the capacity may be slightly higher.