If you need a window air conditioner for a room that's 450 square feet or larger, check out those with ratings of 10,000 BTU and up. Some ACs in this size range come with a slide-in chassis, which makes installation easier: You install a lightweight sleeve first, then just slide in the heavy air conditioner.
The Lowe's-exclusive 10,000-BTU Frigidaire LRA107BU1 (*Est. $280) doesn't use a slide-in chassis, but users don't report any problems installing it. In fact, this reasonably priced unit is the top choice of experts and owners for cooling a room of about 450 square feet. Some 75 customers posting at Lowes.com almost unanimously say it cools rooms very quickly, and expert testers agree that it does an outstanding job. Several owners say it even cools a couple of adjacent rooms nicely. This Energy Star-rated unit comes with a longer than average five-year warranty and a host of features including an automatic thermostat, remote control, 24-hour timer, sleep mode that increases the room temperature as you sleep to save energy, and an alert that tells you when it's time to clean the filter. The most common complaint is noise: "Prepare to turn your TV's volume up when it kicks on," one user cautions.
The runner-up 10,000-BTU Kenmore 70101 (*Est. $300) works nearly as well in one top test, but its airflow to both the right and left are noticeably weaker than the Frigidaire LRA107BU1's. Otherwise, the two units are very similar, with the same Energy Star efficiency rating and all of the same major features. The 70101 also lacks a slide-in chassis, but owners say the unit is compact, lightweight and easy to install. Noise is a problem with the Kenmore, too: "The 'beep' sound emitted every time a button is pressed is extraordinarily loud," reports one buyer at Sears.com. "It will wake up everyone in the room as well as down the hall."
If your window opening is tall and narrow, owners recommend the Frigidaire FRA103KT1 (*Est. $495), one of the few units that Frigidaire markets for slider and casement windows. At 20.25-by-14.2-inches, it can also be installed through a hole cut in the wall. This model packs the same 10,000 BTU cooling power and most of the same features as the LRA107BU1, but the unusually shaped FRA103KT1 costs a lot more, and it's not Energy Star-rated. Even so, it earns a perfect rating from customers at Walmart.com and a nearly perfect score at Amazon.com. Owners say it cools extremely well. The unit's rated for 450 square feet, but a couple of users with 1,000-square-foot houses say it keeps the whole place comfortable.
For an even larger space of about 550 square feet, the 12,000-BTU LG LW1212ER (*Est. $320) -- and the LW1210ER and LW1211ER models it replaces -- receive overwhelmingly positive reviews for both cooling performance and quietness. The new model is identical but now has a 24-hour timer vs. 12 hours and LG has cut its warranty from five years to one. Like most air conditioners in this class, it also comes with a remote control. The only complaint in reviews is that installation can be difficult, although the unit has a slide-in chassis and some users report no problems. Experts say the 2010 and 2011 versions are efficient and cool well, and owners compliment these units' quietness over and over. Initial reports indicate that the 2012 LG LW1212ER delivers similar satisfaction.
The runner-up in this size range, the 12,000-BTU Frigidaire FRA126CT1 (*Est. $355), is a customer favorite at Walmart.com. Reviews of the essentially identical FRA125CT1 (*Est. $330) at BestBuy.com and LRA127CT1 (*Est. $330) at Lowes.com are similarly positive; these models are exclusives for these retailers. The unit quickly cools the advertised 550 square feet, report owners, several of whom installed it out of desperation during the summer 2011 heat wave. Some say it cools off an entire floor of their house, or even the whole house if it's 1,000 square feet or so. This air conditioner offers the same features as the LG LW1212ER -- including an electronic display, remote control, 24-hour timer and automatic restart after a power outage -- and is smaller in size at 19 inches wide vs. more than 23 inches.
In terms of performance, however, one expert test calls the Frigidaire FRA126CT1 louder and harder to use than the LG LW1212ER. Several owners agree, at least on the loud part: "It's like sitting next to a turbine," says one owner at BestBuy.com. Another cautions, "Don't get it for a bedroom...it beeps louder than a microwave." Unlike the LG, the Frigidaire lacks a slide-in chassis, so reviews say it can be harder to install: "This means you will be holding the 60-pound unit from falling out the window until you get the window closed," warns one owner.
It's important to note that window air conditioners are intended to cool a single room, and few homes have rooms large enough to require a unit of more than about 12,000 BTU. For whole-house cooling, experts say a central AC or multiple window units are more effective and use less energy than a single high-powered window model -- even with strategically placed fans.
Even so, plenty of owners with big, open floor plans and vaulted ceilings recommend the 15,100-BTU Frigidaire FRA156MT1 (*Est. $475). One calls it a "snowball-tossing beast," and others agree that it really can handle the 900 square feet Frigidaire claims. "This cooled our whole downstairs in 108-degree weather," writes one owner at Lowes.com. Another uses it to cool his 24-by-36-foot shop with 10-foot ceilings. Not surprisingly, the unit is bigger and heavier than most window ACs. At more than 23 inches wide and almost 18 inches tall, it may not fit in your window but can be installed through the wall; at 100 pounds, installation can be a two-person job although a slide-in chassis makes things easier. The Frigidaire FRA156MT1 is Energy Star-rated and runs on a regular 120-volt outlet, so you don't have to install a special circuit.