I have a portable air conditioner in my bedroom, and I use it only at night when I am sleeping, and only maybe 10 nights a year. I hate to block up the window with the unwieldy vent hose set-up several months out of the year just for this infrequent use. So I was thinking of an unusual set-up. There is a bathroom door going into this bedroom, but I never use that door because there is a secondary door to the bathroom from the hallway. The bathroom happens to have a large window. I was wondering if it would work to vent the a/c unit by cutting a hole in the door between the bedroom and the bathroom and having it vent into the bathroom. I would have both doors of the bathroom closed, with draft-stoppers to block the gaps at the bottom to minimize heat seeping through, and I would keep the bathroom window wide open, so there would be dissipation of the hot air coming out from the a/c hose. I could even add a portable fan in the bathroom positioned so it is drawing the hot air coming out of the hose out towards the window. In addition to not hampering the use of the only bedroom window, this set-up has another attractive aspect. To reach the window, the unwieldy 5.9" diameter hose has to do two gradual S curves from the back of the a/c unit , and this takes up a lot of space. (Sharp curves are frowned upon.) By positioning the hole in the door EXACTLY at the height the hose comes out of the back of the a/c unit, I don't have to have any curve in the hose at all. It would be a straight 12" connection to where it goes into the hole in the door. This would save a lot of space. The two problems with this idea is - if I have to go to the bathroom during the night, I could see the other door to access it, but it would be very hot in there! But how much time would I spend in there? Two minutes? I could take the heat for 2 minutes. A bigger problem is the hole that would be left in the door after the a/c season if over and I remove the hose. You would think I could find a simple white plastic cap to go over this hole, but my search on google has not been successful. All sorts of flanges made for portable a/c hoses, but no simple cap or plug. I would appreciate any ideas for this, and also ask if anyone can see a fatal flaw in this idea!!
In theory this could work. Probably not, and it depends a lot on the details. The biggest obstacle IMO is you need to cut a hole in your bathroom door to find out.
Let's solve the easy part first: You can repair the hole by camouflaging it. Mount a door mirror over it, or cover it with wood and put a picture frame around the wood, like the apartment door in Friends. Maybe something toilet themed. Be creative.
Now for the A/C: An A/C moves heat and moisture from one place to another. Usually to the outside. The two most common examples of moving the heat to another inside space are 1) When they put a cashier's booth in a large underground parking lot and install a window A/C in it, venting to the parking lot. 2) Your refrigerator, which moves heat into your kitchen.
Here's the catch: In both of these examples the heated space is much much larger than the cooled space. In your case, your bathroom is much smaller than your bedroom, and if you sometimes open your bedroom door to enter or leave it makes the challenge even harder by admitting new warm moist air. It all comes down to how effectively that open window works. If you seal both doors tightly and put a fan in the window, there will be no air flow. The fan will mostly create turbulence. It will help a bit. But whether it will work enough comes down to experimentation. If not, the bathroom will become so hot that the A/C will cease to work efficiently or at all.
Well, the best idea of course would be to use it the way it's intended. But anyway. Rather than seal both bathroom doors, you could open the window, install a powerful exhaust fan in it, well sealed all around the edges, seal the bedroom door, leave the other bathroom door open, and open a couple of downstairs windows. This will create excellent air flow through the bathroom, and I think the A/C should work perfectly well.
The spectacle of a powerful exhaust fan installed in your bathroom window with sealant and tape, an extension cord running through the bathroom, the need to actively manage the entire system by keeping the other door and downstairs windows open, .... is all that really more aesthetically pleasing to you than just using the provided hose in your bedroom window?
My advice would be, if the entire plan is the one described in your Question, don't do it. It's a big gamble to destroy your bathroom door for a plan that is unlikely to work very well, or at all.