intake to outake ratio??

hey guys i've decided i'm building my own grw tent n need a little advice.
It's around 3.5x3.5x7ft and i'll be running a 600w HPS in there. I'm planning to have an active exhaust on the roof linked to a carbon filter on the outside. I was also planning on installing some vents on the floor or low on the walls to allow for passive intake. the passive intake only works with a negative pressure inside but i was wondering wat exhaust outake compared to area dedicated to intake ratio would provide quality ventilation. i would also prefer not to have to install a fan for air movement and exhaust fan size is no real problem.
cheers

actually... i have no problem with installing a small oscillating fan. small price to pay to get those buds closer=DENSER to the light.

Everyone seems to say 2 to 1 intake to exhaust. i think that is bullshit. Depends on the cfm and static pressure of the fans you are working with...

i was planning on using an inline fan around 200 cfm and just having three of the walls with passive intake vents... any good?
i saw somewhere how to calculate the cfm required for a particular size room but can't find it anywhere now, does anyone know what cfm you need per m3?
thanks

Yea i'm not exactly sure. But, if anyone knows I have the same question. I'm planning on having 1 out 1 in, both the same cfm. Would that work?

i've read that the exhaust should be a little bigger than the intake, this causes a negative pressure in the room and makes air (fresh) get pulled in through any passive or active intakes. but still cant find the cfm per m3

classclown said:

Yea i'm not exactly sure. But, if anyone knows I have the same question. I'm planning on having 1 out 1 in, both the same cfm. Would that work?

Click to expand...

No it wouldnt work & here is why.

Aside from venting the room one main goal should be isolating the smell & containing it within the room until its scrubbed or ozonated,when you have powered intake & exhaust both of equal cfm the chances of smell escaping are very real,when you connect a carbon filter to the exhaust you are changing the cfm of the exhaust drasticly,now more air is being pushed in from the intake than can be exhausted,the smell gets pushed out through cracks.

The 2 to 1 ratio is a good ratio when using powered intake & exhaust,when using passive i use the same size hole for the passive intake as i do for the powered exhaust,if its a 6 inch fan then i cut a 6 inch passive intake,cutting larger intakes will only reduce any negative pressure within the room & thats a bad thing.

You can also install an adjustable damper in the passive intake to adjust the intake area.

thanks heaps panhead, i'm using a 120mm inline fan as an ehaust with a carbon filter so think i'll cut a passive intake arond 100mm.
i'm guessing you have a carbon filter or something similar connected when using the same size intake, exhaust or, cause the filter will reduce it's capacity do you make the intake smaller.

2 to 1 wich way??

2 exhaust to one intake if your using an active intake/outake.

but if you read the whole post FullMetalJacket sais it would be better to work it out using cfm static preesure of your fans... all i really know atm is that you need more exhaust than intake to get that negative pressure which equals minimal air/odour leaks. I will go on a hunt and try come back with some actual figures

active exhaust (250cfm) of 6"
passive intake of 6"
This is how my grow cab is setup.

what is a passive intake?

Ok I see. I plan on doing a 6" inline fan for outtake, and a 4" (lower cfm) for the intake. You can look at the step by step of my cab in my thread. "Grow Room Design (PICS)"

passive intake means a hole. active = powered ie: inline fans pulling/pushing air. read the GROWFAQ it goes over the m3 question, the static question, and the reasons behind it.

. . . . it should be under the ventilation part but i would read everything in the growfaq to better acquaint yourself.

thanks, actually have looked thrtough it quite thoroughly must have missed it.
looks like i need something between the ranges of 210-350CFM to clear the room around 3-5times a minute. probably loking at closer to the higher walue cause it's a 600w in 2m cubed
1m=3.3ft
1mx1mx2m=3.3ftx3.3ftx6.6ft=72ft cubed
i need to clear this between 3-5 times so 210-350ft per minute
think i'll try a 300CFM

but get a blower not a inline fan. unless you get a industrial inline. the cage blowers and such are meant to pull air through the bend and curves, like a scrubber or a vented hood. the inlines aren't that powerful. i bought my squirrel cage blower on ebay for 40 bucks and it was rated at 250cfm. it blows my 500cfm inline fan out of the water. hope this helps.