Installing a window air conditioner can be simple, even for the novice. But unless you have experience installing one, there are mistakes you could make which could result in damage to the window in which the air conditioning unit is mounted. Or, by making these inadvertent mistakes, your new air conditioner could drop from the window, become damaged, or even injure someone. Follow the suggestions below to avoid making such mistakes. If you plan to install a used older unit, and if you wish to avoid making perforations in your home's siding, check to see if the unit requires you to install an external bracket. Some of these brackets require holes to be drilled into your house siding. Newer air conditioning units often provide supports that fit into the opening of your window, allowing you to install the unit without risk of damaging your home's siding. But, improper installation of these supports, can allow the unit to fall out of this opening when the window sash is raised. Or, if your sill wood is partially rotted and collapses from the weight of the unit, it could not only damage your unit when it falls, but could also damage the window sash.

Depending on the make and model, some window air conditioners can weigh as much as 100 pounds. Never plan to lift one of these heavy units into place without help. When ordering by phone or Internet, never buy an air conditioning unit without first determining its weight. Just as windows vary in size, so do air conditioner units. Never purchase a unit until you have first determined the size of the window space into which you plan to install your air conditioner and the dimensions of the unit, itself. If you purchase a unit that is too large for your window you will be forced to either enlarge the window, or return the unit. If you purchase a unit that is too small, you will have open space between the unit's extensions and the side window sash. Although most new window air conditioning units come with extensions that will occupy the space between the unit and window sash, there will be empty spaces through which hot outside air can enter your home. If you fail to fill this spaces with foam other similar material, your air conditioning unit will operate at less than optimum efficiency.