My windows in my bedrooms are 3' by 3' double hung but the opening I can use is only 12.5 inches. I cannot find an air conditioner that height. Does anyone know where I can buy one. Thanks brutus11

Get a portable A/C unit. It will pump the hot discharge air out the window with a 6 inch hole. That will work with a 12.5 inch space.

You will have to be inventive on this one. Since your windows are typically considered non-standard for window AC's---you can attempt a "professional bootleg" installation. In the "hood" when I was younger---we could not afford the window A/C which actually fit our window---thus, we bought the smaller one and improvised.

You would measure the height and width of the space that you need to fill---regardless of the A/C size. Cut a piece of plywood at least 1/2 inch longer on each angle than needed. I know this sounds a bit gory--but, Home depot sells this thin plywood in colors! White, blue, pink etc. Get the color cut to size and you would need 1-2 extra people to assist. Purchase 4 pieces of the plywood per measurement (height/width) for indoors and outdoors. Most people just secure the outdoor portion, but any preference is OK.
You can have different colors inside and out! Pink will match your room and white can match the house perhaps!

Wedge the A/C between the window opening to hold in place where you want it---even if vertically or horizonatlly installed the air will circulate. The plywood would need to be "welded" with Industrial Strength Adhesive (Clear preferrably), which is waterproof and bonds wood and plastics wonderfully.

Place and Bond the wood where you would normally attach the A/C extensions (which are not long enough anyways). You can also place Installation material between the boards for extra efficiency and energy saving (preferrably)

The wood serves as extra window security, rather than mere plastic extensions.
Also, place a little bonding glue around the A/C unit and the window opening for added security of the window unit. This also beats replacing the central cooling system,
And can aid as a temporary relief during the summer months.

Hope this helps. Good Luck!
Tomy M. Hall, MS