Hi Doog
My MK1 effort was made with a shower cubicle fan, it worked but putting cooker hood filter paper if front of the fan reduced it's efficiency to 0!
My MK3 as in the pics, have 4 fans are from a server rack, rescued from the IT dept. skip/dumpster. (It helps that I'm a geek by profession, btw.)
The power harness allows me to have 1, 2, 3 or 4 fans running should I wish.
They are high volume, not high pressure, (google the Mfr name & model no for the spec)
& with a fleecy-type (lost the packaging, sorry) filter in front of the fans they have a noticeable, but not excessive 'draw'.
After 2 sessions, spraying Vallejo (VJ) concrete, & my own favourite mix of black VJ Polyurethane Primer + Future (nice hard, satin finish), I can report that the fleece catches the overspray, there is no noticeable trace of paint in the end of pipe that goes out of the window.
Noise Levels are acceptable, louder than the radio, way quieter than a kitchen cooker hood.
Now some may think that a Heath-Robinson lashup is over-kill, & probably is for a quick touch-up, the odd figure, etc, but I built it because I now need to be mindful of my house mates & roomies, & I really really don't like the smell of some FUTURE!