Can you slap a furnace/HVAC filter on a standard box fan to create a decent air purifier? You can!
I taped a 20-by-20-inch Honeywell FPR 9 filter to a Lasko 20-inch box fan and ran that combo through our standard 35-minute, five-match test in our 200-square-foot New York test space, with the fan on high. And you know what? It did okay, cutting the initial particulate load by 87 percent over 35 minutes on medium. That’s nothing like the 99 percent reductions our picks achieved on their high settings, and it didn’t reduce particulates as quickly, but the results were better than one might expect.