$25 Air Filtration System




Introduction: $25 Air Filtration System

Simple anti-allergen air filtration system at a fraction of the cost of commercial units. It's not pretty but it does a great job. All parts readily available at your local hardware store or department store.

Step 1: Purchase or Acquire the Following:

- One Cheap 20" box fan ($6-8)
- One very good DISPOSABLE PLEATED 20" furnace filter (I like the 3M ones) ($8-$15)
- Good quality duct tape ($2-$4)

1) The brand of fan doesn't really matter. A cheap one works as well as a good one, and price is no indication of how long it will last either.

2) DO NOT buy some goofy expensive electrostatic permanent filter or a filter that isn't pleated. Good quality Disposable Pleated filters pull far more out of the air. If you don't believe me, prove me wrong.

3) Don't skimp by buying cheap duct tape. You'll end up using twice as much and not get as good of a seal.

Step 2: Assemble the Fan According to the Directions That Came With It, Take the Filter Out of Its Packaging.

Step 3: Align the Filter on the Fan

Most cheap fans will be set up to push air in one direction. Likewise, most disposable pleated furnace filters are designed to handle airflow in one direction. They even have an arrow directing you as to the right way to place them in the airflow.

You want to align the furnace filter on the fan so that air exiting the fan will go the right way through the filter.

Step 4: Attach the Filter to the Fan

Using the duct tape, seal the filter to the face of the fan.

Step 5: Shroud the Back of the Fan.

Since you have added a restriction to the front of the fan, air will want to blow out the back of the fan instead of through your filter. Since the fan is round and the corners are square, the air will tend to try to exit the back of the fan through the corners.

Tape over the corners of the fan on the inlet side, covering the outermost 6" or so of each corner. This will prevent air from exiting the back of the fan, allowing the filter unit to work far more efficiently.

Step 6: Plug Things in and Enjoy Cleaner Air.

Step 7: Replace Your Filter When It Starts to Look Dirty

Usually every month or two. Remember to use pleated disposable furnace filters.

Step 8: Cheap Fans Wear Out.

Pushing air through a filter adds stress that the fan wasn't designed to handle. Expect to buy a new fan every year or so.



    • Creative Misuse Contest

      Creative Misuse Contest
    • Tiny Home Contest

      Tiny Home Contest
    • Water Contest

      Water Contest

    12 Discussions

    Great instructable, useful and simple. I read this and thought "Why didn't I think of this?" I am now:)

    1 reply

    put the filter on the inlet side of the fan and avoid the air escaping issue...plus you don't have all that dust going through the fan...

    Interesting points about filter on front vs back. I made one of these last summer and went with in front because I learned that when the filter was in back, the vortex would actually suck in from near the edges of the front of the box and send large amounts of dust back into the air. I'm sure with modification you could correct this, but the easy fix was to move the filter up front to the exit side of the fan. Any vortex in the back is ultimately drawn back and pushed through the filter in the end. And even though it will burn out the fan motor faster, there is no cleaner fan to start the season than a new one.

    Fulldec's got the idea :-) Ducttape to the BACK of the fan. now, the fan doesn't struggle so hard. with the filter in front, there's an increase in pressure inside the fan case, thus the blowback, and added stress. with the back-filter, there's a partial vacume. to compensate, aome air will be sucked in around the edges infront, but blown right back out, by the fan... so you end up with around a 90% filtered, 10% recycled airflow... run the rig for a few hours, and achieve the same results(the law of averages kicks in) Also, if it starts to get dust balls stuck to the filter, but the filter is still good, you can gently vacume the filter, without shutting off your fan :-) Best you're gonna get with this is a reductoin in dust, dander, and mabey some pollens. those pricey electrostatic filters do work, and have the added bonus of being ion generators(remember those?) so you get a "fresh" smell. Your idea would work in tandem with one :-) think of it as a pre-cleaner post-cleaner. and as a final step, spend thousands on a hepa-whole house, air-filtration system. now we're talking space shuttle clean air. of course, if you Don't have allergies, this'll just cut down on the dusting some. :-)

    Also, the inflow is not as directional and not as strong for most fans.

    Some years ago, I made a similar filtration system, but simpler and quicker. Just turn on a box fan and put a filter on the inlet side of the fan. The fan holds the filter in place. Its easy to see how quickly the filter is loading up. I used the really cheap air filters, not the nice pleated ones, though. Worked great for woodworking dust.


    12 years ago

    Hey, that is just about the coolest thing ever! I SO need to do that!! Thanks!!

    1 reply

    You are welcome. :) - Freed

    True, but with the filter on the inlet side of the fan, then all of the crud you pull out of the air is just loosely sitting there on the back side of the fan. It comes off when you brush up against the fan, and if the fan falls over, the stuff gets knocked off of the filter onto the floor. No such problems with the filter on the front of the fan.

    why not put the filter on the inlet side of the fan? this solves backflow problem