How Effective Are Portable Air Conditioners?

Unlike a window air conditioner or a central heating, ventilation, and air conditioning system (HVAC), all of the mechanical parts of a portable air conditioner sit inside the room you’re trying to cool. This contributes to the noise they can make.

It’s also a reason for less-than-capable cooling. While a window AC uses outside air to cool the coils on the outdoor part of the unit, a portable air conditioner uses conditioned air from the room it’s in to cool the mechanicals. That creates negative pressure that can cause warm, unconditioned air from nearby rooms or the outdoors to flow into the room you’re trying to keep cool.

While window air conditioners have been subject to federal energy efficiency standards for more than 25 years, portable air conditioners have not. In 2016 the Department of Energy set new efficiency standards for them, but they don’t go into effect until 2025. Many manufacturers have already been producing units that meet those standards.

The result? When you’re shopping, you might see portable air conditioners that list a Btu rating according to the new standard—and some that list an inflated or misleading Btu rating. (Btu, or British thermal unit, is a measurement of its cooling capacity.) And during this transition, you might see two Btu ratings listed on the same box.

For example, a portable model that was formerly listed at 14,000 Btu (called the ASHRAE rating, from the American Society of Heating, Refrigerating and Air-Conditioning Engineers) may now carry a DOE rating of 10,000 Btu.

But even with this change, you still can’t compare a portable air conditioner with a window unit regarding Btu. “The DOE’s test conditions for window ACs are more demanding than those for portable ACs,” says Joanna Mauer, who tracks energy efficiency for the Appliance Standards Awareness Project, an advocacy group. “A window AC rated at 6,000 Btu will therefore deliver more cooling than a portable AC unit rated at 6,000 Btu.”

They aren’t for everyone, but some people may have no viable alternatives. If that’s you, keep the following tips in mind to make the most of its cooling capabilities.

Install it right. All portable air conditioners come with a kit that you install in a window. It consists of a plastic panel with connections for the exhaust hose and can be installed horizontally in a double-hung window or vertically in a sliding window. Make sure all the connections are tight, and seal any air gaps.

Get a ceiling fan. Create a breeze by running a ceiling fan. It will make the room feel cooler, but only if it’s rotating in the direction that’s designed to push cool air downward. Many ceiling fans allow you to switch their rotational direction, and most should be set for optimal airflow out of the box. Still, you should double-check whether your model allows this and which settings it’s on to ensure you’re getting the most out of it.

Block the sun. Close the curtains and shades to keep the sun from overheating the room. You might also consider getting darker shades, curtains, or blinds that can more effectively stave off the sun’s warmth.

None of the portable air conditioners in our tests make our list of recommended air conditioners, but if you have no alternative, consider one of these five high-performing models.

At Consumer Reports we test each air conditioner in a room appropriate for its claimed size. We’ve adjusted our testing according to the DOE’s new standard. “We now go by the DOE’s Btu rating,” Regan says. “That means we are testing each unit in a room more appropriate to its cooling capacity.”

In our portable air conditioner tests, we measure how long it takes the appliance to lower the temperature in a test chamber from 90° F to 85° F. We found that it takes at least 20 minutes—and often much longer. By comparison, the best window air conditioners can cool a room by 10° F in about 15 minutes or less.

To read more about the differences between portable, window, and central air conditioners, be sure to check out our air conditioner buying guide. You can also browse our database to see more details on all of the air conditioner models that CR tests.