# advice on passive intake needed

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

1. 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.

2. 4 inch should be sufficient

3. 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. 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. Thanks indic4 I appreciate the advice.

6. 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. 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. A = pr2

Area of a circle equals pi times radius squared.

9. Is there an echo in here? lol

Simon

10.
11. Is that a visual metaphor for being slow?

Simon

12. thanks simon and NJsteez I think I've got it now.

13. I think its a toyota echo. kinda funny.

Evil.

14. Really, you think so? lol

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

Simon

15. 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.

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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. 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