Don’t want to pay for expensive equipment in order to breathe clean air? Me neither.

F. Adam Sopuck

In the first full week of June, the air quality was at times so bad from the Quebec forest fires that I was desperate to act. I began late-night researching (to the hellish sound of screeching raccoons) on how to purify air in one’s house on the cheap. On that smoky night, I found a solution: The Corsi-Rosenthal box. This thing is a Red Green fan’s dream! Yes, duct-taping is involved, and the box is very easy and relatively inexpensive to build. I drove to the Lowe’s to load up on duct tape and furnace filters early that morning. Incidentally, I ran into another motivated soul who was there for precisely the same reason. Essentially, the box involves four furnace filters (of Merv 13 or higher rating) taped together so that they form, predictably, a box, at this point with openings on the top and bottom. The filters in box formation are then secured and sealed to a cardboard floor (again, with tape), and then a box fan (I used a Lasko) is placed on top of them, also secured and sealed with tape. A cardboard “shroud” is cut to the size of the fan and secured on the top of it. Crucially, ensure that the filters’ arrows are pointed inward and that the box fan is blowing upward. The test to see if one did things correctly is to take a bit of paper and see if it sticks to the filters when the fan is turned on. This DIY job will likely save you hundreds, and I can attest to the fact that it works well. I suspect that it’s at least comparable in efficacy to mid-level (i.e., in the range of $350-$500) store-bought air purifiers, but do your own research, of course! Detailed build instructions can be found here: https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

A make-shift household air purifier, the Corsi-Rosenthal box
Photo: F. Adam Sopuck