Yesterday's thread on the Jet air filter brought up the comment I see on most of those threads, that it's cheaper to build your own. That always leaves me with a few questions, for those of us without a spare furnace laying around, where can you buy a squirrel cage fan, and how to you determine real world CFM vs the made up numbers given by the manufacturers?

Also, if I've already got a cartridge filter on my dust collector, why not put in a wyee and use that as a secondary filter? I was looking at the roll your own air filter on Wynn's site, and the ambient filters seem to be the same material as the dust collector filters. Couldn't you just run a quieter motor into your dust collector filter system and get the same results? I'm sure I'm missing something obvious here, I just have no idea what it is.