How do I choose a window air conditioner?

The first rule is sizing. ENERGY STAR says room air conditioner sizing is about matching the room size to the unit size, and DOE warns that an oversized unit can cool the room too quickly without removing enough humidity. That is why a too-big AC can leave a room feeling cool but clammy.

Pick the unit for the room you actually want to cool, not the biggest number on the shelf. Then check efficiency, window fit, and whether the unit’s shape matches your window type. ENERGY STAR also notes that some models use a U-shaped or saddle design that lets the window close more fully, which is useful if you want less noise and a cleaner install.

If you are ready to shop, start with a window air conditioner and compare the listed cooling capacity against your room size. The sibling pages on dehumidifiers, humidifiers for a bedroom, and air purifiers cover the other humidity and comfort choices.

The best buy is usually the smallest efficient unit that can still keep up on the hottest day you care about.