Choosing an Efficient Room-sized Air Conditioner
by Ben Engebreth, New York City 
on 08.14.05
New York City has been breaking electricity usage records lately as a result of the extreme heat and humidity that can always be found in that part of the world in the middle of summer. Having just purchased a window air conditioner in the city myself, I thought I'd review some "best practices" for choosing an efficient room air conditioner.
First off, it's very important to get the right sized air conditioner. Air conditioner cooling capacity is measured in BTUs. Larger BTU units are made for larger volumes (i.e. larger rooms). The Energy Star site has an excellent guide to choosing the right sized room air conditioner based on the room size. Since larger AC units cost more and use more energy, you'll save both by following the guidelines in the link.
Air conditioner efficiency is listed on the side off all units as a number called the EER (Energy Efficiency Rating). The EER is a simple ratio of the BTUs of the unit to the amount of power it consumes in Watts. Thus an air conditioner with 10,000 BTU capacity and an EER of 10 consumes 1000 watts of power -- which is a lot.
The government mandates that all window units have a EER of at least 9.0, but there are plenty of well-priced units out there today with ratings of 10.5-11 to be had with a little bit of looking. These more efficient units will also have an Energy Star label on them because they exceed the minimum standard (9.0 EER) by at least 15%.
The more BTUs or the higher the EER, generally, the higher the price of the air conditioner. However, since most people buy over sized air conditioners (too many BTUs for their purpose) and often don't look at the EER rating, it's possible to both save money on the up front purchase and reduce your monthly electric bill by getting the appropriate sized unit with a high EER.
And remember to keep the thermostat at something reasonable. You're not trying to turn your apartment into an icebox, you're just trying to take the edge off the heat and humidity. If your AC has a timer feature you can use it to cool your place before you get home, but remember that an appropriately sized air conditioner will cool a room pretty quickly.
If you live in drier climates, evaporative cooling may be an alternative (and more energy efficient) means of keeping cool worth looking in to.
For a list of the most efficient window unit air conditioners see the American Council for an Energy Efficient Economy.
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Great info.
Y'know what gets me, though? Walk down Fifth Avenue or in SoHo on a day with a heat index of 110, and you'll find retail stores with their doors wide open, blasting AC onto their patch of sidewalk, hoping to entice you into the cool to buy something.
It's beyond stupid: every summer, you'll see footage on the evening news of a neigboorhood camping out in the streets because another portion of the ConEd infrastructure has collapsed in a shower of sparks or exploding manhole covers.
And yet, some folks think it's perfectly OK to pour the BTUs out into the air, while those of us with sense look for AC units with good EER ratings. Makes me wonder why we bother.
Ian, you remind me of something awful I saw in a store in Ottawa: a small coca cola fridge with soda bottles inside, but it has no doors. It's just sitting there, totally open, the compressor working all the time (you could feel it pouring heat on your feet, meaning that the part of that heat just rose and went back inside the fridge).
Ridiculous design. Whoever created that needs to change career.
Ceiling fans are an energy-efficient alternative to air conditioners when the temperature is hot, but not too hot. Remember, though, that fans (ceiling or otherwise) cool people, not air - a fan does nothing but circulate warm air if you're not standing in front of it or underneath it.
Another simple tip is to turn your AC off if you're going to be away for a while. No use cooling an empty room/house.
Hey. Note that dehumidifiers use less energy than air conditioners; a dehumidifier + fan could do the trick in my neck of the woods, where it's miserable at 80F because of the water condensing on one's skin. Though it wouldn't feel as nice as AC, it would be worth a look.
i'm only half kidding.... whats that street in nyc that has all the people selling plants? man, the whoel sidewalk is green-- time it right (after their waterings) and you have a very cool walkwabout amidst the swelter. Evaporative cooling, just like a swamp cooler (but from plants, so just like the one at the Solar Living Center!)