[Superman]

A friend of mine runs a fairly large county maintenance operation. They service and maintain a bazillion pieces of heavy equipment, not to mention fleets of cars and trucks. He says that most paper filters have WAY more surface area than they need. In fact, they are designed to pass more than enough air volume, even when they are very dirty and plugged. Here comes the interesting part: Their filtering ability gets better the dirtier they are. To a point of course.

This friend relies on the findings and recommendations of manufacturers, suppliers, etc. They recommend waiting until the filter is VERY dirty. WAY dirtier than you guys would be comfortable with.