Box fans don't work especially well with the backpressure. You'll get vastly less air flow. I think the dust-catching products I've seen like http://www.leeval

Box fans don't work especially well with the backpressure. You'll get vastly less air flow. I think the dust-catching products I've seen like http://www.leevalley.com/us/Wood/page.aspx?p=65482&cat=1,42401&ap=1 http://www.leevalley.com/us/Wood/page.aspx?p=65482&cat=1,424... are a lot less restrictive than a couple furnace filters across the front of the fan.