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.

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bradknowles 10 hours ago | parent [-]

At that point, you’re not doing any actual air filtering. Just use them as fans instead.

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gpm 10 hours ago | parent [-]

Merv-13 means it filters at least 75% of the particles passing through it.

For a standalone air filter which is pushing the filtered air into the same room its drawing from, we can assume reasonably good mixing of the intake and exhaust air. Thus to be equivalent to a HEPA-filter it only needs 1/3rd more airflow... Which really isn't much.

This doesn't follow for a a fancier setup where you're taking dirty air and blowing it into a cleanroom or something... but that's not how we're typically using household air filters.

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CoffeeOnWrite 7 hours ago | parent [-]

Is it safe to assume all particles are equally as likely to be filtered, or are there particles that HEPA will filter that a MERV-13 will never filter no matter the number of cycles?

	▲	schiffern 6 hours ago \| parent [-]
		75% refers to the Most Penetrating Particle Size (MPPS), so they intentionally measure at the worst-case size so you don't have that problem. All other sizes are filtered at a higher percent.