*The 5 Gallon Filter*
By: Requa
21 November 02

I have been watching the postings on Air Filters and wondering where to find a squirrel cage fan. I was wandering thru the local Menards store looking for a fan to use for a filter. I went into the Ducting section and found Kitchen exhaust fans and of course Bathroom fans. That is when I came across the n688 impeller exhaust fan and an idea came to me. This is an .8amp 115v fan. With 50CFM output. According to my understanding this would equate to 115v times 0.8amps = 92watts, which sounded livable for the output in a safe room.

Surprisingly enough, the smell of clean air is nice and the output isn’t that bad.


  • 1 5-gallon Bucket ($1.99)
  • 1 n688 Bathroom Exhaust fan (these fans I believe come up to 160CFM) ($ 10.99)
  • 1 Roll of Aluminum tape ($ 5.99)
  • 4-5 Cheap Furnace Filters 20”x25”x1” ($.49 each)
  • 1 Big Blue 20”x25”x1” ($ 13.99)
  • Couple Hepa Filters of Choice.
  • Charcoal Pre filters
  • 1 surplus computer Power cable.

    Here is a picture of the fan I picked up. The N688

    There were two mounting tabs that I beat flat, You could cut these off and the fit would be better.

    Notice that the Black plastic output nozzle is removable. You should remove this to aid in fitting thru the hole we’ll be creating.

    Now you must measure a little over 3” up from the bottom. This is where the center of the cutout will be. The Air output Nozzle is 3” in diameter; since we are cutting it to fit at an angle it will actually be an oval when we are done. I could never explain the mathematics, so I drew a circle and cut to fit.

    I used a pair of tin Snips to cut out the circle after after I drilled a pilot hole.

    I took the detached nozzle and fit it into place in the bucket hole we just cut.

    I placed the Box fan on top of the bucket to find where the Power wires will Poke thru and drilled a hole. ˝” diameter.

    Then I slid (forced gently) the fan down into the bucket. And poked the wires thru the hole.

    Remove the computer end of your power cable and connect the Green to green, white-to-white and black-to-black..

    After this I cut the ceiling cover to fit into the bucket and then set about cutting disk’s to fit inside the bucket.

    Each Successive Layer MUST is sealed around the edges with the aluminum tape.

    I Placed (I did not Pack) a layer of the cheapo filter and a layer of the Blue .1 Micro filter I also cut some spacers using the grating with one of the filters to allow for layers of “dead air”

    I wanted to prevent restricting the air movement too much.

    Layer your filters as you wish, I prefer the Cheap, Hepa, Cheap, etc. My Theory is that when you get to the top, you may want to use a few of the cheap porous ones to act as a pre-filter to grab what large particles it can to spare the Hepa and other filters further down in the stack.

    You can run a 3” pipe from the output nozzle to wherever you need it, the Air will be sucked into the top of the bucket and down thru the filter stack.


  • Allow for Airflow.
  • Do not leave Gaps around the layers. (Tape and seal)
  • Seal the Bottom “ Power-Out”
  • Seal around the Output Nozzle
  • Power it up every once in awhile to test flow while building.

    I hope you can add an improvement to this, I thought it was a great evening project and had a lot of fun. This is by no-means a perfect example, but it is a concept you can build upon.

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