The summer months can be brutal, and climate change is causing historic heat waves in parts of the United States.
Both operate in a similar fashion. Hot air is removed from the room and pushed outside, while cool, dry air is blown into the room. Within either type of unit, you’ll find fans, a compressor, a condenser and an evaporator that manipulate the state, pressure and temperature of the refrigerant. Refrigerants contained within coils absorb and discharge heat from the air. (Ductless mini-split systems, in which air-handler units hang on walls, are a more expensive option, with a compressor and condenser outside.)
Both window and portable air conditioners are widely available, with models to fit most any budget and room configuration. You want to weigh the pros and cons of each, so you don’t buy something in the heat of the moment. If anything, you may find a bevy of choices. That’s why I turned to Rachel Rothman, chief technologist for the Good Housekeeping Institute, and Mary H.J. Farrell, home and appliances editor for Consumer Reports, for advice. Here are their suggestions.
The differences between portable and window units
The basics: Portable units come with a five- to seven-foot exhaust hose and a window panel installation kit for horizontal or vertical sliding windows. They must be vented to the outside (typically through a window, but you can also do it through a wall, ceiling or door). Prices range from $150 to $650, based on quality and the size of the room the unit can cool.
Pros: Relatively easy to set up, because you are only installing the window kit. Most work with existing electrical outlets. Can be stored in the winter.
Cons: “Portable” air conditioner is an oxymoron. Even those on wheels typically weigh 50 to 80 pounds or more. Once the hose is connected to the kit to vent it outdoors, you can’t simply pick it up and move it from room to room. Also, to avoid restricting airflow, portables can’t abut a wall. In a small room, it’s like having an extra piece of furniture.
Efficiency: Compared with window units, portables are far less efficient, because they need about twice the amount of power to produce the same amount of cooling.
Best when: You can’t install a window air conditioner because of design limitations (windows aren’t standard size) or building restrictions.
Tips: For proper efficiency, you need to make sure the exhaust hose is as straight as possible, because kinks can limit the effectiveness, Rothman says.
The basics: Temporarily or permanently installed in a window opening with plastic, adjustable side panels. Prices range from $150 to $450, averaging about $250.
Pros: Window units are cheaper and more energy efficient. They are also quieter, because the noisy components are outside.
Cons: It’s difficult, if not impossible, to mount a window unit in casement or sliding windows. Units weigh 40 to 60 pounds. Unless you are a true DIYer, you may need to pay an installer to ensure that the unit is correctly and safely put in. Some homeowners associations ban them because of aesthetic concerns; they just aren’t pretty.
Efficiency: When Consumer Reports tests air conditioners in the same room size, a window unit can lower the temperature by 10 degrees in 15 minutes or less. A portable takes at least 20 minutes or more to lower the temperature by five degrees. The Good Housekeeping Institute found similar results.
Best when: You have no restrictions on what you can install in or attach to your home. Rooms have double-hung windows.
Tips: Carefully measure the height and width of the window frame when open where you plan to install the unit.
Shopping for a portable or window air conditioner
Size up your space. Measure the square footage (height and width) of the space you wish to cool. Be mindful of high or loft ceilings. If you have an open floor plan, such as a kitchen that flows into a family room, you’ll need to include the measurements of both spaces in your final calculation. Then, look at the square footage in the air-conditioning unit specifications. Says Rothman: “You’ll want to size up in general if you have high ceilings, if it’s near the kitchen where it can get warmer or in a particularly sunny environment. In addition, if the room will be filled with multiple people regularly, you’ll want to size up. If you’re in a particularly well-shaded room, you can reduce capacity.”
Mind your BTUs. BTUs can help you determine whether an air conditioner will effectively cool a room of a certain size. Units with too high a BTU waste power; too weak, and you’ll continually run the machine on full power but never feel cool enough. In general, the larger the room, the more BTUs you need.
Most models list their cooling capacity on the box or website. However, you may notice two numbers that can be confusing. The Energy Department introduced new, more accurate standards in March that go into effect in January 2025, but some manufacturers have already started to use the new ratings.
If you see units displaying two different BTU ratings, Farrell says to use the Energy Department number to compare units. Also note that you should not compare a portable air conditioner to a window unit by BTUs, because the testing standards differ. So, when in doubt, look at the unit’s square footage coverage.
Review the features. Models may come with extras, such as a remote control, timers, an energy-saver switch and sleep mode. New “smart” units can be controlled using an app. A “follow-me” function can measure the temperature both on the unit and the remote to get a more accurate estimate of the room’s temperature. A “check filter” indicator visually reminds you to clean or change the filter. Oscillating vents help move the unit’s airflow from side to side for more efficient room cooling.
If you can't decide
When possible, it’s better to invest in a window unit over a portable one, Rothman and Farrell agree. The bottom line is you pay more for a portable air conditioner to cool the same amount of space, and a portable, even if comparable in specifications, will not perform as well as a window unit. Few can ever achieve optimum coolness.
Still, if the installation will be too difficult or a window unit simply won’t fit with your home, a portable unit can provide some comfort. Farrell is working from home in Sleepy Hollow, N.Y., with no central air. “Because of the way my place is configured, I can have only one window unit,” she says. “Right now, I wouldn’t buy a portable unit, but ask me again in July or August.”
More on heat waves
Our warming climate: It’s not just you — summers in the U.S. are getting hotter, and experts say heat waves will likely become even more frequent and intense. Take a look at what extreme heat does to the human body.
How to stay safe: It’s better to prepare for extreme heat before you’re in it. Here’s our guide to bracing for a heat wave, tips for staying cool even if you don’t have air conditioning, and what to know about animal safety during extreme heat. Traveling during a heat wave isn’t ideal, but here’s what to do if you are.
Understanding the science: Sprawling zones of high pressure called heat domes fuel heat waves. Here’s how they work. You can also read more about the link between weather disasters and climate change, and how leaders in the U.S. and Europe are responding to heat.