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Mead put his alternative together for less than half the cost of consumer-quality purifiers. People have been turning a box fan and a couple filters into a janky air purifier for years, either from wildfire smoke or wanting to make their own, cheaper version of expensive air purifiers. Several people in one Reddit thread last week said they'd been doing this one weird box fan trick for years, and how-to's about it have circulated since at least 2011, when Jeffrey Evans Terrell, director of the Michigan Sinus Center, demonstrated his $25 build.Terrell is using one of several methods; for his, he affixed one HEPA filter to the front of a box fan. Others use two filters taped to the back of a box fan, to form a triangle shape.Thomas Talhelm, Associate Professor of Behavioral Science at University of Chicago Booth School of Business, has been fascinated with air quality and particulates since living in Beijing. He founded Smart Air, a corporation that educates people on indoor air quality and sells air purifiers. "The data on DIY purifiers is very clear: they work," Talhelm said. "They can even rival the $1,000 purifiers." Talhelm spent years making DIY air purifiers and testing air quality and particles on his own. Here are some tips he shared with us:
- Make a good seal around the fan and the filter, with tape if you have to, and if you're doing the one-filter method, use a fan with a flat surface so you can get that seal. "The most common mistake that I see is that people don't have a flat fan," he said. Strapping a flat filter to a convex fan face will just pull air in around the filter, bypassing it for the most part.
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- Close all the doors and windows. "Just by closing doors and windows, indoor air has 40 percent less particulate than outdoor air." He tested this himself.
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- The design shape—two-filter triangle versus one filter on the front—doesn't matter too much for air quality improvement, and neither does room placement. The triangle does allow more surface area and makes the fan work less hard to pull the air through, but slapping a filter to the front works fine, too, especially if they're in short supply.
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- With the front approach, make sure the filter covers the whole face of the fan. If it overlaps, on a circular fan with a square filter for example, that's fine.
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- A weak filter is better than nothing. Since filters are selling out fast, any type would do in a pinch—it doesn't have to be the highest-rated HEPA to work. "If people can only find a furnace filter in Walmart or whatever it's definitely better than nothing," Talhelm said. *