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This is my cue to come and say that if you want to purify your home air, please look at the science first. Do NOT just go buy a HEPA. Chances are you'll waste your money and get little clean air.

Look for MERV and CADR ratings for filters. Then spend an afternoon building yourself a CR box with a box fan, or a narrower one with some computer fans. It'll work better than most commercial purifiers.

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Buying a multistage HEPA purifier is perfectly fine, but first one must get and use an independent air quality meter to measure air quality. This will help one understand which purifiers are helping and which aren't, also how much they're helping. It usually takes several purifiers, including at the source of air entry, to effectively lower the PM levels to very low numbers. Also, the filters must be replaced routinely.

Yep, MERV13 or MERV14 is more than enough if all you're worried about is dust, pollen and smoke.

Because it's not as fine of a filter, far less air pressure is required to filter the air. This results in much, much quieter purifiers.

The endgame of this sort of goal is PC case fans. They've been optimized for decades now to squeeze every last bit of airflow for less and less noise, and they last for a couple decades or more.

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