Filtering Intake Air

Those of you pulling air from outside, what do you use to filter that air? I've been using cheesecloth double layered. I am sure there has to be something better. It must be doing something cause it gets filthy quick. But I assume it's letting a lot of things pass through. Within a week the cheese cloth usually needs changing, which becomes time consuming and expensive.

I used a 10X30" standard 3M A/C intake filter rated for the smallest stuff. A 3/4" piece of plywood with a filter sized cut-out and then screwed into place over your intake works beautifully. I've been having trouble uploading pics but I'll see what I can do.

You can buy washable filters as well to cut down on long term expense.