Window units are by far the most popular. Models can be installed in most single- or double-hung windows and typically come with accordion panels that allow for a secure fit. Some also fit in sliding windows.

Installing a window unit is an easy DIY project. Make sure you measure the inside window dimensions before you shop. Directions and hardware should be included.

Through-the-wall units require opening a hole in an exterior wall, a job that is considerably more involved than installing a window unit. On the plus side, they don’t take up window space, and they allow for a more airtight and secure fit.

Most window models can be installed as through-the-wall units—you just add a frame to support the unit. Small units can be installed by handy do-it-yourselfers. Large through-the-wall units may require professional installation.

Why we like it: • Right size for mid-size rooms • Remote control • Energy Star rating

Portable air conditioners, self-contained, freestanding units, are the new kids on the block. Most have casters, so they can be wheeled into the room or rooms that need to be cooled. They come with a large, flexible hose that is attached to a window for exhausting hot air, much like a clothes dryer is vented. Though they tend to cost more than window and through-the-wall units, they are practical because of their portability and can be taken with you when you move.

Air conditioners remove water from the air as they cool it, which means that most portable units have reservoirs that need to be periodically emptied, though some also come with optional hookups for a drainage hose. Some new models evaporate much of the moisture and exhaust it, greatly reducing the frequency of need to empty a container.