I run a couple of FDM and SLA printers in a closet in my house. I wanted a way to exhaust toxic/smelly fumes out of this enclosed space without having to permanently modify walls or doors. This allows me to vent fumes out of a nearby window using a 4" inline exhaust fan,a couple of lengths of 4" dryer exhaust hose, and a handful of pipe clamps.

This will fit under a door with at least 18mm of clearance. On carpet, it slides easily enough to open the door without removing. Unfortunately, depending on door gap, this won't work for all applications.