Yikes. Putting high pressure drop genuine HEPA filters on a fan like that where most of the air will bypass them defeats the purpose and is a waste of energy and money. Just get a bigger MERV 13 or better filter and cover the whole fan.
Based on his testing, it looks like it achieves purpose just fine, and slightly better than the more expensive option.
> and is a waste of energy and money
His setup has over 5 times the filter area (1,400 cm² at 5 cm thick vs. 300 cm² at 4 cm thick), for $10 more on the filter replacement. Energy use is higher, but it's not clear that it exceeds the savings from cheaper filter replacements.
And by having those gaps in the filters, the fan motor is probably being saved from overheating. Plenty of air still gets entrained through the filters, even with some bypass.
It's kind of like premature optimization when writing a program. Where you think improvements are needed isn't necessarily where they should be. Test your code, find the hot spots, and improve those. With a filter setup, it might see obvious that a good seal is needed between filter and fan. Turns out, that's not always true.
