alt Hacker NewsThose fans will not have sufficient static pressure to be useful. These makeshift purifiers may be great in a pinch (wildfire season and stores are all out), but far from the best.
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The linked PC-fan purifier has been tested and shown to purify air faster than the conventional alternatives, and are not makeshift, so I'm not sure what you are referring to.
From the specs it looks like they are probably closer to higher-static-pressure server fans, the CADR is a few hundred CFM and it pulls 30+ watts. And as with many of these designs, you can compensate for low pressure performance by increasing filter surface area... the greater the surface area the lower the pressure drop. Of course, the problem with this is you are just spending more money on filters, which is the expensive part.
This is indeed the "conventional wisdom," but if you do the math it turns out this is incorrect.
The trick is to use high-airflow MERV 13 filters (ideally 3M 1900, which has high pleat count and low resistance) instead of high-resistance HEPA filters, so axial PC fans can generate enough pressure.