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Some countries don’t have box fans, but have round fans.
“Presenting V1.0 accessible, effective and validated DIY filters using round fans inspired by the #CorsiRosenthalBox. They are the result of international collaboration from designers, engineers and advocates in @TheWHN Airborne Group DIY Filter Team.”. Source here.
For the type of fan, “For gym fans, anything between 80-120w 16-18″ is best. Aim lower for quietest operation. These designs and numbers were tested using a 18″ 45 cm gym cage fan. Best not to go above 120w. Will likely be running setting 1 or 2. Highest power flow is large but unstable & noisy.”. Source.
“Calculated based on 62% filter efficiency but we have particle measurements for Aerostar brand. We’re building and testing in UK,Spain,Canada,Switzerland. “. Source.
“Using ISO 5801 pressure balanced calibrated flow test. Similar to described in this paper .” Source.
4 Filter Build


1 Filter Build


1 Filter Build Video


2 Filter Build (Wedge Shape)


Some creative ideas:
4/ 5 Filter Build
A most excellent idea is this one, by ChurchAndCoVid : “The plywood (OSB) is 21”x21” (53 cm). Fan diameter is ~16” (40 cm) This could go on top of 4 merv-13 filters or a frame with polypropylene sheet.”




This is from here – an excellent build site hosted by Philip Neustrom.


A round fan that might work with a box combination:


A round fan video build below, found by David Elfstrom:


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