Considering it was 101 out today and 110 in the shop, I made a small purchase...21.5" wide
It's now 75* in the office.
I had to do some creative engineering as the window is surface mounted from the outside and this one relies on support from the outside of the window on the lower sash, which it doesn't have. Once again the Kreg jig came in handy and saved the day.
The unit needed a 1" overhang outside of the window. Rather than doing that I gave it a 1" overhang inside, and used the entire window frame to support the weight of the unit, which is centered over the window's center point. I did have to add some flashing on the outside on each side to make sure the rain ran off.
As you can see I cut a 3/4 wide board to run across the top to support the weight of the unit and used kreg screws to secure it.
As mentioned in Tom B's thread, I'll be moving the unit to an opening in the wall at a later (cooler) date. Too bad the units with heating built in weren't cheaper, and I'd have been able to kill two birds with one stone.