Buying Advice: Portable air conditioners

Consumer Reports News: June 20, 2008 11:32 AM

A portable air conditioner that you can roll from room to room might appeal to you if your window space is limited or if you live in a building where regular room air conditioners are prohibited.*

But our past tests of three large portable air conditioners, each with a claimed cooling capacity of 10,000 Btu/hr., showed that they delivered less relief from the heat than their manufacturers touted. What’s more, these $400 to $500 appliances were pricey, especially compared with the window air conditioners we recently tested. (Use our free calculator to determine what size air conditioner(s) you need.)

The portable units we tested had a single exhaust hose that routed air from inside the room over the air conditioners’ condenser coils and finally to the outside. A typical portable air conditioner comes with a low-profile vent adapter bracket that you place in a double-hung window to allow the hot, humid air to  exhaust (generally no tools are required for this installation).

While portable air conditioners might be convenient, those we tested delivered only about half of their cooling capacity—that means they operated with an energy-efficiency ratio (EER) of about 5 or 6. Compare that with the minimum EER of just under 10 for the window air conditioners we’ve recently test (we tested window models with an EER as high as 12).

Why are portable units are so inefficient? The air they exhaust to the outside comes from inside the room you’re trying to cool (as well as from adjacent spaces). The energy used to cool and dehumidify the air is essentially wasted since it gets sent out the vent hose.

What’s more, this setup means that warm, humid outside air will leak back into the room, and that air must then be cooled and dehumidified. The result: inefficient operation.

Some portable air conditioners have two hoses—one that brings in air from the outside to cool the condenser coils and another to exhaust that air back to the outside. (We haven’t yet tested models with this configuration.) This setup mimics the process of a traditional window air conditioner, so these models should come closer to delivering their stated Btu/hr. ratings.

However, moving the air through these hoses can waste energy, so their efficiency levels are typically lower that those of typical conventional window air conditioners.

*If air conditioners are prohibited in your building be sure you know the reason why. For instance, older buildings with older electrical wiring might ban them for safety reasons.

Beyond energy-efficiency issues, there are some others factors to consider when buying a portable air conditioner: Since all the mechanical components on a portable unit are inside the room, the potential for noise is even greater. Note that window air conditioners, particularly those with cooling capacities similar to those for portable models, tend to be noisy, too.

Moisture is another issue. The water that accumulates during the operation of a portable air conditioner goes into a drain tank. Most use this water helps cool the condenser coils so it gets evaporated and discharged through the exhaust duct. However, some designs don’t use this water, so you must empty the tank once or twice a day during normal usage.

All of the models we tested used water to help cool the condenser coil and water was needed for optimal operation. Without this water, the cooling capacity and efficiency of the tested models dropped significantly.

Bottom line: Given these downsides, we suggest you consider a portable unit only if having a window unit is out of the question and a split ductless system is not viable because of cost or installation concerns. If you do decide to buy a portable unit, choose a model that has two hoses and evaporates the condensed water.

Essential information: See our advice on staying cool this summer without cranking the A/C, and share your tips for keeping comfortable, in our forums.

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