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what air filter should i attach to a box fan?

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when california was on fire, rich people bought $800 air purifiers. medium people taped filters to box fans. my roommate from last year said the entire bottom floor of lowe’s was repurposed just for selling box fans and filters.

the unit she assembled went with her when she moved, so now i want to build one, too. i have a theory it will help with cat dander and dust during the not-on-fire seasons. basically i want an air purifier year-round, just not one of these. in 2016, i actually bought an airmega 400 based on that guide for $600 because my then-roommate had a cat and i thought i was allergic and was sick all the time (turns out i had mono), and i really thought i was a rich person. i never took it out of the box and returned it because it was huge and i came to my senses.

anyway let’s build an air purifier.

fan: 20" box fan, lasko seems to be the most common brand

filter: for wildfires, it needs a rating of at least MERV 13. (find a better info source than this youtube video i just watched that i don’t trist because they taped the filter to the front of the fan)

attachment mechanism: start with tape all the way around the edges. what kind of tape? does it really need to be airtight? last year the one my roommate made was not airtight–it was just two strips of grey duct tape. i think i’ll go woth duct tape all the way around to make a seal.

the filter should be on the BACK of the fan, so the fan is sucking air through the filter (not pushing air into the filter) (find a source).

that should be it.

other considerations:

  • our house is incredibly drafty. i bought a bunch of draft foam tape and it’s just been sitting here for a year. all the windows and all the doors leak tons of air. smoke gets in.
  • we have carpet in two rooms.
  • it is incredibly dusty in the shed-thing under the stairs to our upstairs neighbors.
  • it is incredibly dusty under the bathtub where lucy likes to hide. we could clean more regularly and that might improve air quality.
  • there are no screens on the windows. i can see a spider on the wall above me and i’m not wearing my glasses right now so that tells you how close it is to me. at this point i just cohabitate with the bugs. at least we don’t have fleas.

this article on webmd says that “doctors say” that air purifiers are the second line of defense, after you do the work to eliminate allergens from your home. https://www.webmd.com/allergies/features/do-you-need-an-air-filter

future iterative improvements:

add a baffle to improve efficiency.

build a nice wooden housing.

do we need two filters? this woodworker has two, one for big particles and one for little ones.

find a way to borrow or commons a device that measures air quality.

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@judytuna, please post a photo showing the assembled fan filter. I’m not visualizing it.

We have a tall Dyson air pusher (no blades, so not a fan), but I don’t think it will work as a filter.

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my filter is the Honeywell FPR 10 Air Filter. they hide the MERV rating, annoyingly. i chose the highest one in the table displayed at home depot. =P because allergies. but my home is hella leaky so a filter won’t help. anyway.

i saved the packaging.

here are some pictures of it assembled:

  1. the box fan was in the “plumbing” aisle at home depot. it was easy to miss. i walked by it five times and asked three different people for help before finding it.
  2. you tape the filter to the BACK of the fan, not the front: you want to drag air through it, not push air through it.
  3. i taped it all. this might be too much? my brain thought “well then all the air goung through the fan is getting filtered”
  4. is the honeywell10 too thick a filter? is it putting strain on the fan? i did not run the fan before taping the filter on so i don’t know if the noise level is higher.
  5. a baffle? youtube videos…

interesting… you can see the circle of dust trapped on the filter more easily in the picture than in real life!

i’ve been running it by me in the kitchen while cooking, because we have no range hood, and the fire alarm in my room goes off constantly. for cooking i have it on 3, the highest setting.

the rest of the time i leave it on 1 in various corners of the house. it does help with cat poop smell!

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Dyson makes air purifiers too: https://www.dyson.com/air-treatment/purifiers.html