while people seem to be telling you that only disposable filters will be sufficient, i think it's probably worth mentioning that something like an electrostatic particle filter, with permanent plates, or something to that effect, could extend the life of your hepa filter, if used in tandem?

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my rainbow vacuum has a built in air purifier mode, and uses water to filter particles. i'd imagine that something like that would be a great addition.

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radio ionization, iirc, causes particulates to fall, so something like that could be a more permanent addition to your arsenal.

there are permanent electrostatic furnace filters, i guess they are called, that you could be using instead of disposable ones. someone recommended a design with a window fan and a box made out of these square filters.

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just some musings on the subject. i am no expert.