Window units are a good option for cooling a single room, a series of rooms, or an area in the home not served by ductwork. Just like the larger whole house systems, window units have benefited from technology advances as well. However, when shopping for a window unit, you need to look for an EER (Energy Efficiency Ratio) rating, the BTU (British Thermal Unit) capacity of the unit, or the number of square feed it can handle. Fortunately, Energy Star labels are common and will help you wade through the data.
Form factors include units you mount in a window, those that mount through the wall, free standing, and ductless mini-split systems. When shopping for a window unit, it makes sense to research brands and features online using sources like the Department of Energy (https://www.energy.gov/energysaver/room-air-conditioners) and consumer organizations. These seem like simple appliances. but care still needs to be used in buying and using one.