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Comment by hyeonwho22 | Hacker News Reader

I got a CR subscription to look at air filters. For good air filtering you really only need a hepa filter ($20) in front of a fan ($20), but CR only analyses the performance of brand name products ($200).

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HEPA filtration only matters if you have a clean side and a dirty side. Most air filters exhaust clean air into the same room as the intake, so all that matters is clean air delivery rate [0]. It's often possible to get better clean air delivery rate using higher flow through a less restrictive non-HEPA filter.

[0] https://en.wikipedia.org/wiki/Clean_air_delivery_rate

The removal efficiency of the filter is built in to CADR, so say a MERV-14 filter with higher air flow and a HEPA filter with lower air flow can have the same CADR.

The Wikipedia article does not discuss the 2 (different!) methods of calculating CADR but this does: https://frdmtoplay.com/nagivating-air-purification/

For best filtering, place the filter so air is “sucked” through by the fan, rather than “pushed”.

(Quite possibly what you meant; I just found “in front of” easy to interpret in either way)

Not exactly. To be comparable to the good air filter products, you'd want to build a cube of air filters and attach the fan so it pulls air through the cube. Fun DIY project, but it's not for everyone. There's a good YouTube video for it.

The DIY cube air filter even has its own Wikipedia entry:

https://en.m.wikipedia.org/wiki/Corsi–Rosenthal_Box

Next time try your library. Many offer free access over the web.

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