Hello everyone have a question on negative pressure.
I have currently a closet that is 2'W x 2'D x 7.5'H I went to the local hydro store pick up a 6" axial fan made a hole behind the closet almost at the bottom. place the 6" fan there as an intake now I already had a 150CFM 4" centrifugal exhaust fan plus 4" carbon filter rated for 200CFM will I achieve the negative pressure that i want for smell?
Thanks for the advice people.

You need a higher exhaust speed than inlet speed.

170CFM exhaust.
70CFM inlet.

^Would work

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Why do you need to push air as well as pull it, GT? Negative pressure, if intake is sufficient, will allow the air in just fine.

If my math is right, total volume is approximately 30'cu. If he were to turn over about 3x total volume/minute, then he'd have LOTS of negative pressure going on, no need to push that with another fan (more electricity + waste heat, too). Just be sure that intake is sufficient or you'll get noise. 170cfm is easily 3x turnover.

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I really don't know what CFM the 6" axial fan is it doesn't say but i think it has to be a little more then 200CFM that sucker blows. Also I notice that the carbon filter when on the exhaust fan it slows ithe fan down quict abit. I have the filter so that the exhuast fan suck out of the filter throught the ducts and out on top of the closet clean.

I know that passive intakes just takes for a opening or open door for air to come in but if I made a hole in the bottom of the closet with no fan blowing into it won't smell come out that hole if left exposed?

No, not if the fan is moving air out of the room in sufficient volume, otherwise there wouldn't be negative pressure. Try pushing the air through the filter instead of pulling it through.

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you mean having the exhaust fan sucking up all the air in the closet., and into the filter? If that's the case then once the air travels into the filter where does the filter air goes if the carbon filter is in the closet.?
cause the carbon filter is caped on one end one way is locating the filter outside the closet. but the reason it's inside is to hide it from being seen

What? Um... yeah.. I think. What I mean is like this.. Grow box/room --> exhaust fan --> filter.

Just put the filter in line with the fan, but have the fan push the air through the filter, don't try to have it pull the air through the filter and then the fan itself. If no air goes through the filter, then how does it work? Where does the exhaust ultimately end up? Every set-up I've seen has duct work in which a filter could easily be placed, so I guess I'm not quite understanding what you've got going on there.

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it really depends on the type of fan that you are operating...axial fans dont have a lot of back pressure so having them pull air through a scrubber would be pointless. an inline fan would pull the air better through the scrubber and in this case the clean exhaust would be ducted outside of the tent/closet/cab. if sufficient negative pressure is attained within your grow enclosure than no air would ever be able to escape the passive intakes because they are always drawing air into the tent to be cleaned.

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there is also a filter design i saw somewhere on RIU that might work well with an axial fan. its some scotchbrite cloth sewn together like a pillow case, filled with activated carbon and fastened over the exhaust. people said it worked very well, i think its called my $3 carbon scrubber...

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That was panhead's thread. I need to learn more about fans. Especially if I want to keep my title here at home as Queen of Fans.
(I create a wind tunnel effect so we don't have to turn on the central A/C.)

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