I hang a Lasko Products 20″ box fan at the ceiling line of the mid point of all four walls of my shop, then duct tape a high efficiency furnace filter to each side of each box fan to seal it up and, voila, clean air! I change the intake side about once every 4-6 weeks (depending on my work load) and the exhaust side about every 12-16 weeks. I’ve run these “filters” 24/7 for about five years and have only had to replace one fan so far. They really do a great job.
– John Barrett