Heavier window air conditioners need extra support so that the window is not the only thing holding the unit in place. You can buy support kitsfor different-size units. Before you place the air conditioner in the window, add the support brackets, which are easy to install from inside the room. Even if you live on the third floor of a building, you can safely install and support a window air conditioner.
Remove the support brackets from the package. You will have two brackets and four screws. Use the heavy-duty brackets for 12,000 to 24,000 BTU units and small brackets for 5,000 to 10,000 BTU units.
Place the first bracket on the left side of the window where the edge of the air conditioner will sit. Use the screwdriver and two screws to attach the faceplate to the inside wall just below the windowsill. Then do the same for the right side. Note: Try to attach the bracket to a stud in the wall. If you cannot do this, use plastic screw anchors.
Place the bracket arms out the window and adjust the rubber feet so that they fit against the outside wall.
Place the air conditioner in the window so that it rests on the brackets. Center the air conditioner and close the window.