Noticed the abysmal indoor air quality as measured this morning by gadget we bought after last year's wildfire smoke turned the sky a Blade Runner orange for several days. Visibility outside is next to nil right now from all the wildfire smoke. So I dug out the box fan filter contraption I built last year. It's bulky as all get-out, but it brought the air quality to excellent throughout the house in about an hour.
Last year instructions for building these things were all over the Internet. But really, all you need is a big square cheapo plastic box fan that you duct tape down on top of a cube of large HVAC filters. Total cost (depending on the thickness of the filters you opt for) should be ~$30-60. We used huge 4-inch thick HVAC filters, so the cost was a little more for ours.
