A window air conditioning unit is, in many ways, a terrible technology. It blasts cool air from only one location, as opposed to the many vents of central air. These heavy hunks of metal hang precariously over sidewalks—something I think about whenever I walk the streets of New York, look up at the many window ACs, and ponder the fact that they were installed by amateurs. But when summer comes and your apartment has no central air, the alternative is suffering (or a bunch of big, dust-collecting fans).Many of the same companies that produce window ACs also make portable air conditioning units that don't have to sit in the window. I was only vaguely aware of these machines until this weekend, when the heat wave that pushed temperatures to 90 degrees F in May forced us to consider cooling options for our suddenly roasting bedroom. We wound up with a 8,000 BTU Frigidaire portable unit. Is this kind of air conditioner right for you?Our main driver in choosing this AC wasn't portability.

It was another of the problems with window units: They take over your window and, depending on your style of window, you can't open it until you take out the AC in the autumn. That just wasn't an option for our one-window room, so we decided to seek alternatives.The Frigidaire portable looks like a mini-fridge on wheels with a vent in the front. The controls are like those of a typical window unit: You can set the temperature and switch between fan and cool modes. This unit also comes with a dehumidifying setting. On the back there's a filter where air gets sucked in, and a port where you have to hook up the exhaust hose: a big, thick dryer hose-like tube that has to run to the window.Our AC also came with a piece of plastic that fits into your window. It's about 7 inches tall and slides to adjust to the window's width. There's a hole where the exhaust hose locks in. Once that's in place and you close the window on top of the plastic piece, you can turn on the machine; it starts blowing cool air out the front and blowing the hot exhaust though the hose, out the hole, and to the outside world.

This is where we get to the problem with portable ACs: "portable" is relative. The machine creates heat that has to go somewhere. That's why your window AC unit is in the window in the first place—the exhaust comes off the back and goes out into the atmosphere rather than filling your house. cost of replacing a air conditioning unitA portable AC is portable in the sense that it can roll around, allowing you to change the point where cool air is blowing. clean home ac unitBut it's also tethered to the window (or another opening like a screen door). lock window with ac unitIt can only go as far as the exhaust hose stretches, which in the case of ours is about 5 feet.For us, that works. We were looking for a solution that wouldn't sacrifice an entire window all summer long, and now we can still open the window whenever we want even with the plastic piece in there.

I don't know if I'd call it "portable," though. Yes, the unit can roll away from the window as far as the exhaust hose extends, but that's a bit of pain, as the bulky hose is hard to adjust. (It's also not necessary, because the 8,000-BTU Frigidaire has plenty of oomph for one room.) If I wanted to move it to another room, it'd have to sit near the window there, and I'd have to readjust the plastic piece to fit a different window. But I wouldn't do it twice a day to move the AC between the living room and the bedroom.These things are a bit pricey, too. During our hunt for the portable AC, Target was selling (and quickly selling out of) a bare-bones 5,000-BTU window unit for $110. We got the 8,000-BTU Frigidaire on sale for $260 at Best Buy; it typically costs $300. Most portables you see will be that expensive or higher, if only because companies typically don't make them smaller than ours.[Note: Commenters have asked about a couple of other issues with portable ACs. Subjectively, our portable certainly feels like it's using more energy to pump more air.

For objective numbers, compare Frigidaire's portable AC to the company's window unit with the same capability—8,000 BTUs to cool 350 square feet. The window unit uses 6.2 amps and 708 watts in cool mode. The portable, 8 amps and 895 watts. The other issue is water that collects inside the machine during the dehumidifying mode. You've eventually got to hook up a hose to run that water out.]If you find yourself in a situation like ours, where you need to cool a room but a window AC won't do, then a portable is definitely an option. You'll probably pay more for it, but it's nice to keep your window. The promise displayed in pictures of these machines is a false one, suggesting a gadget that can roll around to bring the chill anywhere in the house. The smaller photo on the back of our Frigidaire box (seen above) is more realistic, showing the AC sitting in the corner, the big hose snaking up to a window. If that sounds better to you than hanging a big metal box out your window, then a portable AC might be right for you.

Just know what you're getting into before it arrives.The statement above is the greatest misconception we saw regarding portable air conditioners and it results in a lot of 1-star ratings: people don't realize that, even though a portable air conditioner is not a window air conditioner, you MUST have a window to use a portable air conditioner (although, a sliding door or any other way of venting the exhaust to the outside will do as well). We wanted to make that clear early on, so that, if you don't have the option of venting your portable air conditioner to the outside, you can head on over to our report on fans instead, to find the one that will keep you the coolest. When considering how to cool a home, there are two main options: central air conditioners (which cool the whole house from a central location) and smaller window or through-the-wall air conditioners that cool down individual rooms. We cover both of those types of air conditioners in their own reports, but there's also a third alternative -- a portable air conditioner.

These are similar in scope and cooling capacity to a window air conditioner, but their more modest venting requirements make them easier to install -- especially in rooms where installing a window unit is either undesirable or impossible, such as apartment units where they may be prohibited. The best portable air conditioners can be set up quickly by just one person and can be moved around to cool a different room as needed, although they're still heavy in spite of having wheels. A portable air conditioner doesn't commandeer a large section of the window (like a window air conditioner does), but a portable AC still needs access to outside air. Each portable unit comes with a window kit, which mounts one or two hoses to a small panel that's installed in a window. Some experts prefer the dual-hose style because it provides slightly better performance. says that, while that's true in theory, in practice the difference is actually very slight. In our research, we found that single-hose models often rate as well or better than many dual-hose portable air conditioners, and typically cost less.

All air conditioners, including portable air conditioners, pull excess moisture from the air. This is stored in a water tank that must be periodically emptied (machines will shut down when the tank is full) or drained continually through a hose running outside. Portable air conditioners with a self-evaporative system minimize the need for emptying, though under more humid conditions, the water tank may still need to be emptied occasionally, and more frequently if the humidity is exceptionally high. Some portable air conditioners have dehumidifying functions that pull excess moisture from the air without cooling it. If you are primarily interested in that, we cover dedicated dehumidifiers in their own report. In doing the research for this report, we quickly found that expert reviews of portable air conditioners offer only half-hearted recommendations, and user reviews aren't much rosier. Like window air conditioners and central air conditioners, the cooling capacity of a portable air conditioner is measured in British Thermal Units, or BTUs.

, portable air conditioners aren't held to the same rating standards as window units or central air systems, so there's often a disconnect between their claimed BTU rating and the size of room a portable air conditioner can satisfactorily cool. McCabe notes that even different models with the same BTU rating will vary in their actual cooling capacity. That means that the disparity between the BTU ratings of window and portable air conditioners renders traditional sizing guidelines somewhat moot. Instead, where a 6,000 BTU window air conditioner might be great for a small bedroom, testing shows that you may need to turn to a 10,000 BTU or better portable model to get the same degree of cooling. These performance shortfalls aren't a result of poor manufacturing, but a byproduct of having a unit that's designed to vent hot air to the outside while sitting entirely in the room it is trying to cool (instead of being half inside and half outside). Still, as most experts and users say, if a portable air conditioner is your only practical option, it's a lot better than having no air conditioner at all on a hot summer day.