[Carolyn Barber] recently interviewed a 15-year-old who has been making Corsi-Rosenthal boxes for people in his community that are at risk for COVID. Not only is it great that a teenager has such community spirit, but it is also encouraging that [Richard Corsi] and [Jim Rosenthal] made an open-source design that can help people at a greatly reduced cost.
If you haven’t seen one of these boxes, it is essentially a box fan inside a cardboard box with MERV-13 filters on all sides. While these high-quality filters aren’t as efficient as HEPA filters, the box makes up for it by moving a prodigious amount of air and by being much less expensive. The article says you can build a unit for $60 to $100, which is considerably cheaper than other filters with similar performance.
There’s been at least one research paper on the efficacy of the filters and the results were generally quite positive. Schools are taking a great interest in these boxes because they are inexpensive and effective. Of course, the filters don’t last forever, but one of the creators estimates in a classroom with 25 students, a three-year run of the box would run about $4.46 per student per year. Not a lot to pay for clean air.