They do work well, and a 10-minute air change sounds about right. The airflow characteristic of the shop comes into play here, you want the unit to circulate the air throughout the shop, with no "dead air" spots.

It's pretty easy to make one out of a used furnace blower. WOOD magazine even published plans a few months ago.

: In spite of a lot of effort to keep the dust and airborne debris off the wet
: varnish, I still get enough of it to be unsat. I have cleaned the shop and
: built a temporary enclosure, with filtered air blowing in. The problem is,
: I have to go into and out of the enclosure to bring the spray unit in and
: out, or for other reasons. Doing so allows more dust to get loose, like
: from my clothes, etc. I have been thinking about installing an air
: filtration unit that filters the equivalent of one shop volume of air
: every 10 minutes or so, and not bother with the pain in the butt
: enclosure.

: Has anyone had any experience with air filtration systems, like the JDS or
: Penn State units? Do they work well enough to be useful during varnishing?

: Any thoughts?

: John