Keep in mind, this is all with a basic filter literally rubber-banded to the most basic fan. It seems likely that someone could enhance the effect. Jim Wells, a retired economist in Maryland who has been tinkering on fan-filter builds with his physicist brother, has a setup with two units to circulate air through the room. Why not? They’re cheap.

Physics poses some obstacles here. A fan trying to push air through a thick medium like filter-stuff (or pull it through) can start to overheat, or get too noisy for a church choir rehearsal or a classroom. (I built one with a HEPA filter a couple years back to deal with smoke from a California fire season, and I didn’t think either of these were much of a problem.) The Wellses attached a step-down transformer to their fans to reduce the standard 120-volt power supply to just 100 volts. That slowed and quieted them. They put a 5-inch MERV-13 filter on the front (not the back, as Rosenthal does; there is in this matter some conflict), and then measured levels of particulates 2.5 microns or larger—that’s “PM2.5”—in micrograms per cubic meter. “Good air, fresh air, in Annapolis runs 5 to 7,” John Wells says. “In a 10-foot by 12-foot bedroom, I got it down to 0.01 on the meter.” That’s obviously not peer-reviewed proof over time, but it’s a real difference.

Like any kit-bashed solution, attaching a filter to a fan with tape isn’t going to end the pandemic. It’s not the end of any story. Filters have to be replaced regularly; that increases the cost and management a bit. And merely reducing the overall amount of particulates in a room doesn’t guarantee that you’re reducing the amount of virus enough to keep people from being infected, says Lidia Morawska, director of the International Laboratory for Air Quality and Health at Queensland University of Technology. Other risk-reduction measures, like mask-wearing and physical distance, are still critical. “I wouldn’t stress the purifier over other actions,” she says. “People tend to cling to something simple and easy and say, ‘This is the solution.’ But nothing is a single, simple solution that works for every environment.”

(Morawska acknowledges that even before Covid-19 she practiced a level of social distancing from sick people and strategic positioning near and around vents and HVAC systems. Everyone, including her family, thought she was a little weird. Who’s laughing now?)

“An important parameter in all of this is time—how much time people spend sharing the environment,” Morawska says. That opens up a panoply of options. Shorten the amount of time people are in a space—kids in a classroom, workers in an office or on a factory floor—and ventilate the space on their breaks, because that trades possibly infected air for fresh. “This is perhaps an even more effective intervention, and less costly,” she says. But a filter, even a DIY one, she acknowledges, is another layer of risk-reducing protection—another relatively easy addition.

Someone could get nuts with this. “It’d be great if we could find a company to make low-cost portable air cleaners out of box fans and a well-designed box the filters fit into,” says Corsi.

“There’s a lot of attention on portable air cleaners now for classrooms. They might be 650 or 700 square feet, 25 kids in them. Oftentimes they’re under-ventilated. In these cases, portable air cleaners might drop the particle levels in air by 50 percent. I like the idea of the makeshift one, because some school districts are so poor they just don’t have the money to buy 1,000 portable air cleaners.”

Home marijuana growers, surely you’ve come up with some clever air-purification and handling tech. Makers, furloughed engineers, tinkerers, where you at? Remember how people wanted to build hospital-grade ventilators, and that turned out to be way too complicated? This isn’t. The components here are basic—the electric motor at the heart of a fan, maybe stepped down with a transformer to not blow so hard, fan blades, a metal frame to hold a panel of filter media, or a bigger box with panels on three or four sides, and a mount for the fan parts. That’s it. Make sure it all clips together with a good seal, and it’ll do … something.

We shouldn’t have to, of course. The money should be there for schools to be well-ventilated and have room for kids to be physically distant. They should be able to afford air purifiers, or have them provided. People shouldn’t risk their lives to go to work. But even if we wish it were otherwise, as a president said once, it is what it is. All of us have to do something, because if no one else is coming to help, we’re it.

More Great WIRED Stories