Portable air cleaners (PACs) with a clean air flow rate of 2.6 air changes per hour (ACH) in a classroom can reduce the amount of airborne particles a person breathes in, by up to 66%, according to one study. DIY air filter tips: Quiet PC fan filters: For low-noise air cleaning, use PC fans instead of traditional box fans. But air filtration and careful masking protected the rest of the family, Liesl told The Sick Times: “We have so many different air filters running through the house, along with ceiling fans on all the time, windows open.”