How to Buy a Portable Air Conditioner

Portable units don't compare well to window air conditioners

As a group, portable air conditioning units don't receive the best reviews from owners. The main complaint is that they don't cool as well as window units do, an assertion we see repeated almost everywhere. Portable ACs do a good job of taking the edge off a hot room, owners say, but they don't chill a room like a window unit can. Most owner reviews say the best application of a portable air conditioner is for those who need to reduce the temperature enough to go to sleep and be moderately comfortable -- but portable cooling units can be very noisy, and they usually won't make a room truly cold. Portable AC units are also fairly fussy, because they need to vent exhaust outside and usually must be drained of water removed from the air in the cooling process.

What size for your room?

You can buy a small 5,000- to 8,000-BTU window AC for less than $150, but portable air conditioners don't get much cheaper than about $300. While the smallest portable air conditioners aren't much of a deal over small window units, prices for larger models are more competitive with equivalent window units. Keep in mind, however, that you'll need more BTU if you go with a portable air conditioner than you would for a window unit in the same room. For a 300-square-foot room, you should look for about an 8,000-BTU window unit, but you'd need a 10,000-BTU portable air conditioner.

When estimating BTU requirements, err on the high side for particularly sunny rooms or if you live in an unusually hot climate. The same holds true if it's to be used in a room with heat-generating appliances or electronic equipment. Keep in mind, however, that bigger isn't necessarily better. An oversized air conditioner won't dehumidify the air as effectively, so the room may become cool and damp. The chart below offers a rough estimate of the cooling power needed for your room size, although the manufacturer's rating may be higher. Owner reviews are consistent with this chart, and many comments indicate that the (higher) manufacturer's rating can understate how much cooling capacity you will actually need.

Important features

Here's what expert reviews say to look for in a portable air conditioner:

• Look for a model with casters or wheels. Along with handles, they'll help you move a portable air conditioner from room to room. But that doesn't mean using a portable air conditioner in different rooms is easy; all portable ACs are quite heavy and require a window venting kit to be installed.

• Look for a portable air conditioner with oscillating louvers or multidirectional airflow. Either will circulate the air and cool the room faster. This is especially important because portable air conditioners don't produce as much air volume as window units. Combining a ceiling or box fan with an air conditioner can also help with even cooling.

• Digital controls let you set the temperature and timer more precisely. However, keep in mind that digital controls are more prone to failure than manual controls, and most portable air conditioners have one-year warranties. A remote control is nice to have, as well -- just make sure not to lose the remote if your portable air conditioner doesn't have on-unit controls.

• Be sure your unit has a venting or exhaust hose and a window-adapter kit. If you don't want to empty water buckets, look for an optional water-drainage hose or a system that exhausts water outside. Some portable air conditioners have an auto-evaporative system that minimizes the need to empty buckets, but they're not always effective, especially in humid climates.

• Duct tape is your friend. Owners say duct tape can be particularly helpful for sealing gaps during installation of the exhaust hose. Weather-stripping around the edge of the window kit can also help keep cold air in and hot air out.

In general, portable air conditioners aren't as effective as window air conditioners. If your only option is a portable AC unit, look for a model with an adequate BTU rating for the size of your room. Choose a larger unit than you think you need if your room gets a lot of direct sunlight or contains heat-producing electronics and appliances.

How portable air conditioners work

Like window air conditioners, portable AC units draw in the surrounding air and cool it, discharging heat outside. The portable air cooler dehumidifies the air, and the collected water (also known as condensate) is removed from the unit using one of two methods. In the first, a bucket or tray inside the unit collects water, which must be manually emptied frequently. In the second, the unit evaporates the water and exhausts it through a hose. Some newer models can recycle the condensate and use it to produce cool air, but reviews indicate that this feature doesn't work flawlessly, and sometimes a tray or separate draining hose must be added whether or not the air conditioner includes this technology. Portable air conditioners must also vent the resulting hot air through an exhaust hose, which extends outside a window, door or air vent.

Even though portable air conditioners are easier to install than window units, they're not quite as mobile and trouble-free as you might hope. You'll need to place the unit somewhat close to a window so it can vent hot exhaust outside (portable AC units come with an exhaust tube and plastic or foam insert for your window to accommodate that). Because all air conditioners also dehumidify the air, unless your unit includes a self-evaporating feature, you'll have to either drain water into a bucket or out a window with a drainage hose. Lastly, while portable ACs can be wheeled from room to room, they're heavy (50 to 90 pounds on average) and bulky; most portable cooling units have a 12- to 18-inch footprint and are about 30 inches tall.

A high energy efficiency ratio (EER) means that a portable AC unit will cost less to operate in the long run. However, engineer and columnist James Dulley says EER isn't measured the same way for portable air conditioners as it is for other types: "There are no formal standards for these tests as there are with window air conditioners, so the EERs can actually vary depending on many factors." Still, EER ratings are helpful when viewed in comparison with other portable air conditioners, even if the ratings are taken only as a general indication of efficiency.