Groo:

Good idea, but you have to have the window A/C condensor cooling air intakes boxed so that they draw air from the outside. On standard window A/C's the condensor air intakes are on the side of the window unit. On "through the wall" mount A/C units, the air intake is usually about 1/3 of the outside face of the unit and the discharge is about 2/3 of the outside face of the unit.

They make room A/C's that have flexible duct work that can be hung out of a window or any opening, but they are expensive, obstructive to the living area, and noisy since all the working parts are inside the house.

You can buy casement window A/C's but they usually cost 2 or more times what a regular window A/C costs, and they are only available in 7,500 BTU's and larger. They are also a pain in the butt to install because they stand tall.

If you can, remove the sliding portion of the casement window, measure the opening, and place the largest standard window A/C unit you can fit in there. You could also remove the whole window and use plexiglas where the A/C ends. Because of the way you will have to mount it, be sure it has support on the outside so it doesn't tip out and fall. If you need an extension cord to plug to your outlet, buy those specifically made for heavy use and buy the shortest cord that will work. You will be suprised how hot the plug portion gets when using an extension cord. I have a 9 foot 14 gage for my bedroom A/C and it gets really warm, but not hot where the A/C is plugged into it.

I do not recommend anything smaller than 14 gage wire and nothing longer than 9 feet. If you have to go longer for a window A/C with an extension cord, go to the hardware store and have them make one up (Only as long as necessary.) for you using three-wire 12 gage and heavy duty 20 amp plug and receptacles at the ends.

Good luck!

Bountyhunter