I am building cubes that take 20x20 furnace filters on some of the sides, and incorporate a 20 inch box fan on one of the six sides of the cube.
Primary motivation is summertime wild fire smoke.
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I ran a filter array like I am taking about for about 9 months, inside my house, last winter. I burned about 7 cords of wood in my wood stove, we home a geriatric long haired cat, and the filter array made it through pollen season after having triumphed over heating season.
I have filtered more particles out of the air in the last two months than I did in the previous 9 months.
I have two potential customers asking "how many dollars?" to own a filter array of their own built by me. I will probably never sell 200 of these. So on the one hand I want to come up with a system, a plan, a template, a pattern; but I don't need to build an elaborate jig and bring in an air compressor and an air nailer.