Our guest bathroom doubles as my darkroom when we have no guests in town. Building codes here allow that if a bathroom has a window, ventilation is not required and this bathroom has none. My darkroom goes up and breaks down in a matter of 10 of 15 minutes and for the most part I am quite happy with how it functions; that is with the exception that I have yet to solve the ventilation problem. Long hours in the darkroom can get pretty stuffy. I am curious if there are any other "Temp" darkroom people out there that have found solutions to this issue. I have seen several posts here for the air filters, which so good, but I am looking for a solution that will exchange the air. I can not make holes in the walls. However, the door coming into this bathroom has a 1" gap at the bottom which I now stuff with towels to block light. I'm thinking an exhaust could be made to push air out this opening. Any thoughts people might have would be greatly appreciated.