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Working Out Cubic Feet For Extraction Fan

Discussion in 'Growing Marijuana Indoors' started by Ciarán69, Jan 31, 2019.

  1. #1 Ciarán69, Jan 31, 2019
    Last edited: Jan 31, 2019
    So I got a free 5inch extraction fan. But I was curious about a smaller one, which led to working out the cubic feet of my tent.

    I'm totally shit at maths (even with a calculator!) & my tent is 1.9x1.9x5.1 foot which is 15.5 cubic feet. Then / by 3 = 5 foot. So I only need a fan that will extract 5 cfm every 3 minutes?

    Am I wrong? Because that seems really really small & I have no need for a 5 inch fan.

    Any help would be great.
     
  2. #2 MickFoster, Jan 31, 2019
    Last edited: Jan 31, 2019
    You're wrong. It's length x width x height. So if my room is 8' x 4' x 7' it would be 8 x 4 = 32 x 7 = 224 cubic ft. In your case, assuming you're talking about feet when you list it 1.9 x 1.9 x 5.1 - let's round it off to make it easier. 2 x 2 = 4 x 5 = 20 cubic ft.
     
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  3. #3 Ciarán69, Jan 31, 2019
    Thanks for the reply
    So to round it off I've multiplied 2ft x 2 ft = 4 x 2 = 8

    Like I said, maths & me dont mix.

    Can I ask how many cubic feet do you think 2x2x2 is? I just dont get it!
     
  4. #4 MickFoster, Jan 31, 2019
    Wrong again - look at my first post again since I edited it. A 2 x 2 x 2 is 8 cubic ft. 2 x 2 = 4 x 2 = 8.
     
  5. #5 Ciarán69, Jan 31, 2019
    Again thanks for taking the time.

    See?!? Maths & me. I put 2x2x2 instead of 2x2x5ft

    So my tent is 20 cubic feet & then to find the cfm I divide by 3 which is 6.5ish?
     
  6. #6 MickFoster, Jan 31, 2019
    No. Your cubic feet is 20 - your fan only has to extract 20 cfm. Where are you getting the "divide by 3"?
     
  7. #7 Ciarán69, Jan 31, 2019
    I googled "how to choose extractor fan grow tent"

    "To calculate multiply length x width x height of growing area e.g. A room that is 8' x 8' x 8' will have a volume of 512 cubic feet. Your extraction fan should be able to adequately exchange the air in an indoor garden once every three minutes. Therefore, 512 cubic feet / 3 minutes = 171 CFM".
     
  8. #8 Vee, Jan 31, 2019
    [​IMG]
    Best vent extraction thread on the web:

    Ventilation 101 - Growroom Designs & Equipment - International Cannagraphic Magazine Forums

    good luck
     
  9. #9 Ciarán69, Jan 31, 2019
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  10. #10 BrassNwood, Jan 31, 2019
    Every foot of vent piping slows the flow as do any elbows. The filter if used drags it down by 30% roughly. Hot lamps like HPS or MH need more rapid exchange then LED-COB will.

    My original grow boxes I kept replacing-stepping up the fan size until I was nearly at 1 CFM per 1 Watt of light before it kept things cool enough.

    A to large fan with speed control beats a to small fan that has the plants roasting come mid summer.

    BNW
     
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  11. #11 MickFoster, Jan 31, 2019
    That's absolutely correct if you're looking for a fan that takes 3 minutes to extract all the cubic feet of air. However CFM means "cubic feet per minute". I never heard of that formula but given the small size you have, I'm sure it will be fine. Good luck to you. :)
     
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  12. #12 StickyBudHound, Jan 31, 2019
    Last edited: Jan 31, 2019
    The formula calculating room air exchanges is: CFM x 60 (min) ÷ area volume (L x W x H) of the space.

    Plug in the CFM rating of the fan you're wondering will be enough for your space and the volume of your tent. This tells you how many times per hour air will be replaced in the tent. As close to 1 air replacement per minute is what you want.
     
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  13. #13 Talkative, Jan 31, 2019
    Last edited: Jan 31, 2019
    rule is 1 times per minute minimum, 3 times max. I run less than 1 due to noise. Great discovery was peppermint oil in an electric oil burner. Smells great in there and they say peppermint discourages pests.
     
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