DIY: Carbon Air Filter - CHEAP, and EFFECTIVE!

Discussion in 'Growroom Setup' started by THContent, Jun 17, 2010.

  1. THContent

    THContent Banned

    Security is important to marijuana growers, and odors can lead the police or unwanted neighbors straight to your grow room. There are a number of 'odor solutions' out there, but they can be quite costly. Here is a simple method you can use to build your own carbon filter. It will take you about half an hour to construct it, and it will cost $20 to $30 dollars. And it is completely safe.

    Aside from its main advantage of being ultra cheap, this method is also very versatile. It utilizes the exact same activated carbon filters that are used in professional air cleaners, without paying the huge prices. It can be adapted to practically any ventilation system. You do not need any crazy tools to build this - anyone can do it.

    For supplies, everything is easily available at a store like Home Depot. You will need the following:

    1 activated carbon filter - ( found near humidifiers, air, and hepa filters )
    1 small roll of aluminum screen
    1 four inch ventilation end-cap
    1 four inch duct connector piece
    1 roll of duct tape


    No tools are required. A pair of scissors and a measuring tape are all you need.

    The carbon filter I purchased is a 'universal' replacement filter for HoneyWell air purifiers. Since I didn't pay the hefty price for a professional unit, I will cut this to size. It was originally 16" high and about 48" long, so I cut it right down the middle. When the first filter is expired, I will have a replacement ready to go.


    The next step is to cut your aluminum screen to size. I chose aluminum because it will be strong, and will still allow good air-flow. You could substitute chicken mesh or something similar. Since my (cut) carbon filter is 8" high, the aluminum will be cut to 12". The carbon filter will go in the middle 8" of this screen, with 2" coming out of each end to connect to the duct pieces.


    Now we will attach the aluminum screen to the duct pieces, with duct tape. (This might be the first time you have actually used duct tape on ducts!) Do your best to keep it straight as possible.


    It will seem a bit flimsy at the beginning. Continue to wrap the aluminum screen around and around, taping it every few inches. You want it to hold firm.


    After a few wraps it will be fairly sturdy, and able to hold its own weight. However, don't drive your truck over it! Treat her nice and gentle like a Christian schoolgirl.


    The ends of your screen may have little strands of metal poking out, threatening to impale you. Add some more duct tape to cover this up and to finalize the DIY carbon filter. Soon it will be done.

    Now it is time to wrap the activated carbon filter onto our device. Conveniently, the filter I bought came with a couple of velcro straps, so I used them to hold it on. This will be convenient to replace when the activated carbon is expired.


    After she's all sealed up, throw on a bit more duct tape around the edges of the carbon filter, to seal up any gaps. Only tape over the edges, because you want the air to flow as easily as possible. Air does not flow through duct tape. Here is the finished product.


    Time to hook her up to the grow room exhaust! In this case, it is being hooked to a 4" square duct. (That is why I used a 4" round to 4" square connector piece. You may need a different piece to suit your ventilation setup, but a million sizes are available.) Just slide her onto the vent, and tape it down nice and sturdy. Duct tape is your reliable grey friend.


    After she is attached and fire up, things are looking good. It is working nice, hooked to a 60 CFM fan, and you can feel the air flowing out of it lightly. The fan was not slowed down too much, but obviously a carbon filter will add some back-pressure to your vents. I haven't tried this with a slower blower (under 60 CFM), but 60 CFM is not a lot.

    I just hooked this up today, so I don't know how often I will have to replace the carbon filter. The box the filter came in says to replace every two or three months. It does seem to make a difference though. Outside the grow room does not stink like a skunk anymore. There is almost no smell at all, except the faint odor of duct tape adhesive. I'm sure that will go away after a few hours.

    Using this method, everyone can now build their own activated carbon filter. Its quite easy, and you can build it any size you need, to fit any grow room and any type of duct. Could it get any better than that?
    • Like Like x 5
  2. THContent

    THContent Banned

    And keep in mind, you do not want a fan with a high CFM rating, 60-140 is good, the carbon filter needs a millisecond to make contact with the air in order to scrub it properly (most efficiently) the slower, the better. So I say stick with under 100 CFM for a filter this size. If you have to go over by a little say 150, not a big deal.
  3. endive

    endive Registered+

    Thank you!

    Simple enough, even I can do it!

    I have a small area, this filter set-up is perfect. The lower volume in-line duct fan is a great idea, a bigger centrifugal fan would probably implode my garden.

    Thanks again!
  4. neceros

    neceros Registered+

    Wow! Thank you for this.
  5. flyingimam

    flyingimam Registered+

    ditto on this design!

    but I have a somewhat relevant question:


    Would one be able to use a 120mm computer case fan with CFM rating of 103 to effectively pull/push air thru and get deodorized air on the outside?

    or a sturdier inline fan of similar CFM is required?

    we're talking $20 vs. at least $80 in cost.

    and FYI, for purposes of this post, the venting system will only be used to deodorize the air without actually having an exhaust outside of the closet box (no attic, outdoors, wall connection), aka enclosed air filtration
    Last edited: Jul 12, 2010
  6. Siceee

    Siceee Registered

    Its really hard to use a small computer fan on a carbon filter.

    Im running out of ideas on making a carbon filter. The easy part is making the filter but the hardest part id finding a cheap fan that can efficiently push air through the filter WHILE keeping temperature low

    I feel stuck on this :(
    • Like Like x 1
  7. jackpuck

    jackpuck Registered

    Great info! Thank you
  8. Blazed Deafy

    Blazed Deafy Registered+

    Maybe you should add two exhaust fans on both ends of this similar design for exhausting the odor? whatcha think dude :jointsmile:
  9. garfield24

    garfield24 Registered


    Love the post, thx! One questions, with this setup what would you say is the max room size this unit will filter? Just setting up my first room on over 25 years and oder is # 1 priority.

    Thanks :)

  10. DrSuess

    DrSuess Registered+

    home made fan question

    do es any one know if using a old desk top comp shell full of lined with a1" cotton and loaded with activated carbon like in some fish tanks. With a powerfull 6" inline 440 cfm pulling out the top?
  11. azdesertdweller

    azdesertdweller Registered+

    this is so cool

    i am SO gonna use this....probably 2 of 'em....thanks for the info:thumbsup:
  12. curto25

    curto25 Registered

    CFM is CFM it will push what it says but I say if you have no suction it isn't going to do any good or too much ventilation for it to push through no good either.
    Last edited: May 5, 2011
    • Like Like x 1
  13. WickedJack

    WickedJack Registered+

    Could this be used as a closed air scrubber meaning it doesnt lead out to a external location..

    My closet can be vented into the crawl space but I'd rather not drill any holes thru walls

    Im gonna try this & see anyway :)
  14. THContent

    THContent Banned

    Yes, it can be vented back in to the room. Scubbed air is scrubbed air is scrubbed air.... However, you do not want to keep recycling the same air around the room, that will suffocate the plants eventually. Think of a person with bad breath being locked in a closet, you have an air scrubber in there to filter out his bad breath but his carbon dioxide keeps getting pushed around the room, eventually the bastard will die.

    I am sure you will figure something out to get fresh air moving in and out.
    • Like Like x 1

    XXXJAYXXX Registered+

    For those of you looking for a cheap fan to run this thing.. In the same Isle you bought your ducting at home depot.. they have small inline duct booster fans.. I have seen them in 4, 5 and 6 inch models.. Its basically just a piece of ducting about 8 inches long with a fan built into it.. I have a 5 inch and it pushes 120cfm... it was 16 bucks.. and would PERFECT for this application as you would be able to use the fan itself as the top end of the filter.. Great post! Cheers!
  16. Rumpl4skn

    Rumpl4skn Registered+

    Wouldn't the inline fan have to be at the bottom of the filter? Mounting it at the top, it would pull air into the chamber, but it would not force it out. It would also pull air in from outside the filter as well, in the other direction.

    I like using that inline duct fan, but it has to be between the grow room area and the filter, to move the air towards and through the filter.
  17. Mal420xl

    Mal420xl Registered+

    doesnt matter if its at the bottom or top only the direction of flow. as long as it pulls air OUT of the space you want scrubbed and thru the filter. thats how he has it set up from what i can see.
  18. Shovelhead Jed

    Shovelhead Jed Registered+

    I'm a bit confused about the placement of the scrubber. I have seen them placed two differant ways: WAY #1) this way the carbon scrubber goes at the top of the grow area, so your hot/stanky air gets pulled by your inline exhaust fan through the scrubber, then through your air cooled hood or cooltube, & then ducted to your fan & out of the room. WAY #2) the scrubber is on the other end, so the air is sucked through the light hood/cooltube, the ducted to your exhaust fan & through the scrubber before exiting the growroom. Can somebody tell me which way is best? Thank you. Cheers, S.J.
  19. determinedtogrow

    determinedtogrow Registered+

    I would think either way would work just depends on the amount of room you have to work how stealth you want it to be. Because regardless It will still filter the air as long as there are no leaks.
  20. TOPPDOG11

    TOPPDOG11 Registered+

    How would I figure out what size filter I would need when I have a 6" inline fan that has a CFM of 240. My cabinet is 4'hx3'wx14"d.

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