Buying a bigger room air-conditioner than you need won’t necessarily ensure your comfort. A model that’s too big will perform less efficiently and effectively because room units work better if they run for relatively long periods of time rather than continually switching off and on. That process, called cycling, can happen when the air conditioner’s thermostat tells it the desired temperature has been reached, or when you simply decide it’s cool enough and shut it off. Either way it’s less efficient than running fewer times a day for longer periods of time. All the starting and stopping is also harder on the equipment, which in turn reduces its life span. So choose a model that’s designed for the size room you want to cool, set the thermostat at a comfortable level…and let it do it’s job.