DIY box-fan air purifier for about $40
Michigan Medicine · Tutorial · YouTube title: Build a Do-It-Yourself Air Purifier for About $40
Why it's here
HN people link it during wildfire smoke and air quality threads as a practical, cheap fix, though a few doubt how rigorously its effectiveness was shown.
What it covers
A University of Michigan Medicine demonstration of building a cheap DIY air purifier from a box fan and a HEPA or high-MERV filter using hardware-store parts. It explains why this helps against dust, smoke and viruses and ties it to local air quality readings.