advice on passive intake needed

Discussion in 'First Time Marijuana Growers' started by newinhere, May 7, 2011.

  1. #1 newinhere, May 7, 2011
    Good day folks. I have a small grow box and am ready to cut some holes for passive intake but before I do, I could use some advice on the size and number I should have for my size box.
    Box is 4'x5'x6' (120cubic feet)
    600w Hps cooled by a 4"sunleaves windtunnel
    stale air being removed via a separate 4" windtunnel (200cfm) and filtered through a 4"x12" phresh filter (also 200cfm)

    So, how big a hole do I need? How many should I have? and if I cover the intake hole with some type of filter (to keep out bugs and dirt) will that inhibit the passive air intake? And finally, what type of screen?filter should I put over the intake tube.

    Thanks a bunch for any thoughts...this is my first time.:confused:
     
  2. #2 gho0ost, May 7, 2011
    4 inch should be sufficient
     
  3. #3 newinhere, May 9, 2011
    any thoughts on the type of filter I should be using over the intake? Could I use a screen from an old window? or do I need something with smaller holes like a hepa filter? I'm just scared that it will inhibit airflow into the box? Thanks.
     
  4. #4 indic4, May 9, 2011
    A window screen won't inhibit your air flow enough to matter. I don't use any screens on my passive intakes but I have a relatively sterile environment.
     
  5. #5 newinhere, May 9, 2011
    Thanks indic4 I appreciate the advice.
     
  6. #6 NJsteez, May 9, 2011
    A four to six inch hole will be adequate. I use two 90 degree black PVC bends to light trap my passive intake, I used pantyhose cut down and stretched in between both PVC bends for my scren.
     
  7. #7 SimonC, May 9, 2011
    The rule of thumb is twice the intake area as the exhaust. Area of a circle = Phi x R^2, where R= the radius.

    So, if we have a 6" hole, its area is as follows:
    3.14 x (3 x 3) = 3.14 x 9 = 28.3in3

    As for filters, furnace filters work well. They can be had in a variety of sizes. Good luck.

    Simon
     
  8. #8 NJsteez, May 9, 2011
    A = pr2

    Area of a circle equals pi times radius squared.
     
  9. #9 SimonC, May 9, 2011
    Is there an echo in here? lol

    Simon
     
  10. #10 NJsteez, May 9, 2011
    [​IMG]
    :rolleyes:
     
  11. #11 SimonC, May 10, 2011
    Is that a visual metaphor for being slow?

    Simon
     
  12. #12 newinhere, May 10, 2011
    thanks simon and NJsteez I think I've got it now.
     
  13. #13 evilhoodlem, May 10, 2011
    I think its a toyota echo. kinda funny. :)

    Evil. :smoke:
     
  14. #14 SimonC, May 10, 2011
    Really, you think so? lol

    And people wonder why I come to this forum. Can't make this stuff up.

    Simon
     
  15. #15 stikyWeedFinger, May 11, 2011
    I have been trying to figure this out and I will try to explain this. Are these holes enough to adequately vent air with my exhaust fan.
     

    Attached Files:

  16. #16 Motherhugger, May 17, 2011
    Nice advice here.

    Kinda afraid to say anything else, or else I might get a car picture response. LOL

    I like the diagram of the box - that's uber helpful and certainly easy to follow.

    Just make sure you're using good nutes too. AN is the one that I use, but I know others like other brands too.

    godo luck!
     
  17. #17 bobtheslob, May 17, 2011
    Can you explain this further ? I have a 4" exhaust running with a 4" carbon filter on a fan rated 110CFM - I have 4 x passive intakes at the corners of my cab which is 2' x 2.5' x 1' - My intakes are 2" diameter.

    Area Exhaust = 12.5 squared inches Area Intake = 12.5 squared inches - Are you saying I should have at least double the intake currently exhibited ? My plan is to add some active intakes i.e. 5CFM 2" pc fan to aid the intakes - Will this be enough ?

    I don't really have the space to cut more intakes...

    Any input / advice would be kewl :)
     

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