How much cooling power do you need? The power of an air conditioner is measured in BTU, short for British thermal units. The higher the BTU, the larger the area it can cool. But bigger is not automatically better. It's important to match the size of your air conditioner to the needs of your room: It must be powerful enough to keep your space cool, but not so large that it shuts off too soon (which leaves too much moisture in the air). The Energy Star website provides the appropriate BTU capacity for different sized rooms, how to accurately calculate room size, and how to compensate for factors such as shade, sun and room usage.
How large is your window? Measure your window opening before you start shopping, as some extra-wide units won't fit in smaller windows. Most window air conditioners are designed for windows that slide up and down. Look for a casement window air conditioner if your windows slide to the side or are hinged. If window mounting is not possible or is undesirable, consider an air conditioner that mounts through the wall. However, in-wall room air conditioners are often costlier than equivalent window air conditioners and have other drawbacks, as outlined in the introduction of this report.
What about the electricity? Air conditioners draw a lot of power, so you need a nearby outlet that can supply it satisfactorily. All of the models in this report work on 115 volts, the standard voltage for residential electrical service in the U.S. However, the circuit also needs to be able to handle the air conditioner's current needs (measured in amps). If the wiring isn't rated to handle that, or if the circuit is shared with other appliances, you might need the help of a licensed electrician to sort things out. It's also best to pick a window that's in reach of the air conditioner's cord. Using an extension cord isn't the greatest idea, but if necessary, be sure to use a major appliance extension cord that's rated to handle the current draw of your air conditioner.
Keeping your air conditioner in good shape. Maintenance is uncomplicated for most in-wall and window-mount air conditioners, but a little regular cleaning is important to keep mold under control (especially in moist climates). Most built-in filters require washing once a month; replace disposable filters at least once a season or as the manual recommends. Clean the drip tray thoroughly at the end of summer to remove mildew, dust and pollen.
Elsewhere in this report: