Cracked the casement window problem for my portable AC

Casement windows here too, and I went a slightly diferent route with mine. Instead of a rigid sheet I used a piece of thick foam board insulation cut to the opening, with a plywood strip laminated around where the hose adapter sits so it had somethig solid to screw into. Worked fine for two summers, though I ended up replacing it last year with a sheet of 5mm polycarbonate after the foam got chewed up at the edges from taking it in and out each season. One thing I learned the hard way with the hole for the hose: measure the adapter collar itself, not the hose, and drill undersized then file up to fit. My first attempt left a gap around the collar big enough to whistle when the unit was running flat out. A bead of silicone around the flange sorted it.

For sealing the edges I found the foam weatherstripping works best if you put it on the panel rather than the window frame, so the sash compresses it evenly when it closes. I also left my panel sitting on the sill with a couple of rubber door stops wedged under it to take the weight off the sash hinge. Those old casement latches can be forgiving but mine started dropping slightly with the panel pressed against it. Mine swings outward the same way, so the panel sits inside and the wind pushes it against the frame rather than trying to blow it out, which is one small mercy with these windows.

I went even lazier with my awning windows and bought one of those fabric seal kits, the canvas sheet with a zip in the middle for the hose. You stick self-adhesive velcro around the inside of the window frame, press the fabric to it, zip the hose collar on and you are done. Took me maybe half an hour the first time and about five minutes each season after that. Since the fabric just peels off the velcro, the window still swings open whenever I want fresh air, which is the thing I could never solve with a rigid panel. It is not as tidy as a proper acrylic sheet, I will admit. The fabric sags a little in the corners and my wife thinks it looks scrappy from the lounge, so I ended up trimming it to sit closer to the frame edges. Also worth checking the velcro adhesive on an older painted frame, because mine started lifting after a hot spell and I had to go over it with a few strips of the stronger outdoor tape. For a rental or anyone nervous about cutting their own holes it is hard to beat though. Mine lives rolled up in the linen cupboard from May to September and comes back out looking fine. Third summer now on the same sheet, only replaced the hose collar once after the dog got at it.

Reading this with envy becuase I've got tilt-and-turn windows and I'm still stuck on the duct tape and cardboard stage, which sags after a week. One thing I'm nervous about is cutting the acrylic myself, the sheet near my window woud be a long cut and I've heard it can crack if the blade grabs. Did you use a fine tooth blade or anything special, or just go slow? Also curious how you dealt with the edges going cloudy from the filing, mine would prolly look terrible in a clear panel. Might just copy the notch idea for the latch though, that's clever.

To the person worried about the blade grabbing, mine chipped badly until I stuck masking tape over the cut line and went slow with a fine tooth blade. Came out clean after that.

Other thing I learned with mine: the exhaust hose was way longer than it needed to be and all that hot air sitting in it was warming the panel and leaking back into the room. Cut the run down as short as I could and the room cooled way faster.