>>6317655>How would a lay person be able to spot one that is separated?
I composed this graphic that I hope is clear. The fans outlined in red are ones that you should avoid. They clearly have their motors mounted in the path of the incoming air flow. If they're used for a spray booth, there's the strong possibility that paint and solvent can build up on them.
The fans with their motors mounted outside of the air flow typically have a protrusion extending out from the fan housing, as noted in the upper left green box.>I was going to just use an overhead stove fan with moderate CFM for a spray booth project
I suggest not using an overhead configuration for a spray booth. First, an overhead exhausted spray booth has to work against gravity, so you need a more powerful and thus expensive fan. Also, because the filter is above the piece you're spraying, there is a chance that loose particulate can fall onto your paint job unless you remember to remove the piece you're spraying before you shut off the fan.
I recommend either a cross draft configuration where the fan is mounted at the back of the spray booth or a down draft spray booth where the fan is mounted in the floor of the spray booth. The down draft spray booth lets you get away with a less powerful (thus less expensive fan) due to being able to take advantage of gravity.
Check out this page on spray booth design. It's pretty helpful and covers fan location, calculating static pressure, flow rate etc.http://www.modelersite.com/Abr2003/english/Spray-booth-design_Eng.htm