UPDATE - it's finished - just finished the run of ductwork to the trap door vent assy. outside. This is all 4". I had a local HVAC sheetmetal place build the box to my design - It's 38" long. I bought a Tjernlund blower - made in USA. Anyway, the flex section leading into the blower is OE grade 6-ply 304 stainless as used on truck exhausts (I had a piece of that laying around), the flex from the outlet of the blower to the 90* bend I bought at Lowes - it's HD flexible dryer vent hose - I needed something that could bend easily - it's actually plenty HD enough for this. The 4" tubing is 16-ga. aluminum mandrel-bent stuff from a local company that bends all kinds of tubing. All connections are screwed & sealed with aluminum tape. It works great. It'll pull in smoke from 3' away from the enclosure & send it outside. This is an updraft booth basically - I'm sure it will work well for doing small spray paint projects as well. Check it out:
