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Window air conditioners are an economical way to cool your room

If you want to cool off a bedroom, living room or office, a window air conditioner is a great solution. The initial unit costs less than a large whole-house air conditioner or a portable air conditioner, and a window-mount unit runs on less electricity than both.

A window air conditioner temporarily mounts on your window sill, cooling down the room it sits in. On the front of the unit -- which faces into the room -- is a grill to pull in air, which gets blown out through vents. The best designs let you adjust louvers on the vents to aim the cool air where you want. The back of the air conditioner hangs outside, with silver fins that help keep the unit from overheating but don't draw air into the room. Window air conditioners also pull excess moisture out of the air as they lower the temperature. By bringing the humidity down, the room becomes more comfortable and less sticky. This excess moisture evaporates or drips out the back of the unit.

Most air conditioners are made for standard windows. Installing a window air conditioner in a standard window is pretty straightforward. Most are designed for a window that slides up and down. By opening the window, setting the unit on the ledge and closing the window, the top pane helps hold the air conditioner in place. Plastic curtains, which come with the air conditioner, slide out to the sides of the window. These, along with a little foam tape, seal around the air conditioner to keep hot air and debris from sneaking in through the cracks and keep more of your cold air in the room.

Casement window air conditioners are a special case. For windows that slide to the side or are hinged, there are two options for window air conditioners. The first is to buy a regular window-mount unit and custom fit a piece of wood or Plexiglas to cover the opening above the air conditioner. The second is to get a casement air conditioner. These are tall and skinny, and often include curtains that extend above the unit to seal the opening. Casement air conditioners tend to be more expensive than traditional window air conditioners with the same cooling capacity, but sometimes fit better in the window. These units also aren't as common as traditional air conditioners -- none of the expert tests include casement air conditioners in their comparisons, and few models have a significant number of owner reviews to accurately gauge performance.

Window air conditioners are grouped by their cooling power. This is measured in British thermal units (Btu). The higher the Btu, the more powerful the air conditioner. To find the right size for you, match the square footage of the room you want to cool to the correct Btu. When shopping for a new air conditioner, experts say the most common error shoppers make is to purchase the wrong size unit for their space. If it's underpowered for the space, it will have to work too hard to cool the air properly. If it's too large, it will turn off before the room is adequately cooled and dehumidified.  Here is a guide to sizes:

Small window air conditioner: Also called mini air conditioners, this size is the lightest and least expensive. With cooling capacities at 6,000 Btu and under, these are designed for rooms up to about 200 square feet.

Medium window air conditioner: Ranging from about 7,000 to 8,000 Btu, these are ideal for rooms around 300 square feet.

Large window air conditioner: A large air conditioner with 9,000 or higher Btu has enough cooling power for rooms 400 square feet and above. This size is typically heavier and more expensive.

Spending more money on an air conditioner doesn't necessarily guarantee a better appliance. According to reviews, several budget-priced options still have excellent cooling performance. More expensive units often include extra convenience features, however, such as a timer and remote control. For many owners, these are worth the additional cost. A few brands, such as Friedrich, get excellent scores in expert tests but are difficult to locate, even in large metro areas. All of the air conditioning units in our report are 115 volts and plug into a regular household outlet.

For an air conditioner that is even more temporary, can be moved easily and doesn't block the view, consider a portable air conditioner. Our report names the best models and tells you what you need to know to pick the best unit. If you want to cool more than one room at a time, read our report on central air conditioners to see the top units and discover how to buy the best one.

To find the best air conditioners, ConsumerSearch looks first at professional tests. Here, experts compare different units in side-by-side tests to determine cooling performance, noise levels and the ability to operate in low power conditions. From there, editors compile owner reviews for insight on specific models, searching for window air conditioners that are easy to install, user-friendly and reliable. As a final measure, we make sure each of the top models is in current production and easily available throughout the country.

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