Independent Confirmation. I’ve always suspected that what I’ve “discovered” is so basic that people must’ve known about this before. Lo and behold, doctors at the University of Michigan recommend that people who suffer from allergies make a purifier for $25 with a furnace filter and a box fan.
Getting independent confirmations of results is always important, and their live tests with a particle counter are convincing. However, their test is with a MERV filter, which catches less than HEPA filters. The upside is that they let more air flow through. I suspect that’s why his numbers are low, but not as low as my tests with a HEPA.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.