If you need an indoor filter that will handle wildfire smoke within your room here is a quick and dirty solution you can whip up in a hurry for minimal cost.
you need a 20" (common size) box fan (you can pick these up fairly inexpensively).
a 20" MIRV 13 rated furnace filter.
MIRV 11 will more or less do in a pinch but not as well.
Some duct tape.
Tape the filter to the BACK of the fan where the air goes IN. Follow the directions for airflow direction on the filter. Tape up all the air gaps around it and any holes in the fan body itself.
run the fan on low or medium at most! more than that might damage the filter or the fan. Do keep an eye on it. Mine works fine but make sure the motor is not getting warm. It will clear out a closed bedroom fairly quickly on low
Not perfect, not ideal. but it works and it's easy. (i have one of these at home I can pull out for quick additional filtration in addition to my main hepa filter)
a "Corsi-Rosenthal_Box" Box can be made with 4 of these filters and a fan at the top but that's beyond the scope of this toot. They're fantastic but more costly and harder to build quickly.
-m
Rockmaster Mike
npub163…6k39u
2026-07-15 16:40:05 UTC
Author Public Key
npub163psw7xtvhpwlmyjapz7frx0f4sm6c3t62qwq8x6sjzwaakttq2sg6k39uSeen on
wss://relay.ditto.pubPublished at
2026-07-15 16:40:05 UTCEvent JSON
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"content": "If you need an indoor filter that will handle wildfire smoke within your room here is a quick and dirty solution you can whip up in a hurry for minimal cost.\n\nyou need a 20\" (common size) box fan (you can pick these up fairly inexpensively).\n\na 20\" MIRV 13 rated furnace filter. \n MIRV 11 will more or less do in a pinch but not as well. \n\nSome duct tape.\n\nTape the filter to the BACK of the fan where the air goes IN. Follow the directions for airflow direction on the filter. Tape up all the air gaps around it and any holes in the fan body itself.\n\nrun the fan on low or medium at most! more than that might damage the filter or the fan. Do keep an eye on it. Mine works fine but make sure the motor is not getting warm. It will clear out a closed bedroom fairly quickly on low\n\nNot perfect, not ideal. but it works and it's easy. (i have one of these at home I can pull out for quick additional filtration in addition to my main hepa filter)\n\na \"Corsi-Rosenthal_Box\" Box can be made with 4 of these filters and a fan at the top but that's beyond the scope of this toot. They're fantastic but more costly and harder to build quickly.\n\n-m",
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