If a window isn’t a great option or if you just want something more permanent: I use mine in a small space and just went big, cut a dryer vent hole in the wall. It’s actually fairly easy to do, I got an inexpensive louvered vent on amazon (10-15 bucks I think?), used a compass to draw the hole outline (4 1/8”), and cut with a jigsaw.
I’ve never done anything like it before, and it only took an hour and a half tops.
The only things that were tricky: be sure no electrical wires are inside the wall, and align the holes really well between inner wall and outer wall.
Tools:
Drill with a long bit (that’s how I aligned the holes, I drilled straight through both walls)
Compass
Jigsaw
Louvered vent kit like this: Whirlpool 8212662 Flush Mount Louvered Flapper https://www.amazon.com/dp/B0049I6LL6/ref=cm_sw_r_cp_api_Ea6qAbXGZWM4E
Screwdriver to install the vent kit.
Optionally, a 4” hole-cutting bit on your drill might be easier, but I didn’t want to go out and shop.