Indoor Rethinking my ventilation- need advice

[McTavish]

Hi All,

I’m just finishing up my first indoor grow in a converted tall fridge, during the first grow it quickly became apparent that my ventilation wasn’t great. (Computer fan exhaust passive intake- struggled with temps and air exchange) so before my second grow I want to make some adjustments..

I’ve purchased an in-line fan for exhaust + cf and am going with a passive intake but want to get this right..

I’m struggling to get my head around this 1 point:

Reading posts about ventilation there seems to be an abundance of people giving the same advice on ventilation, that with an inline fan for exhaust and passive intake the passive intake should be much larger than the size of the exhaust.

If I had a 4inch exhaust fan and say an 8inch passive intake, how would that create the negative pressure that I’m after?

Maybe I’m just being dumb but wouldn’t a smaller or same size intake create the negative pressure that’s desirable rather than a larger intake????

Can anyone help me get my head around this??


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[bad dragon bzzz]

i think you got muddled somewhere along the line,passive = no fan.a crack in the door an open flap.an intake fan isnt needed in standard size tent/cupboard.

 

[McTavish]

i think you got muddled somewhere along the line,passive = no fan.a crack in the door an open flap.an intake fan isnt needed in standard size tent/cupboard.

Hi, I’m talking about the size of the passive intake in relation to the size of the exhaust. So I’d have a fan pulling air out of the top and a passive intake at the bottom for new air to enter


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[bartlancertp]

I have two 6" passive intakes, and a 6" fan pulling out and it works fine. For a 4" exhaust, I would use two 4" or one 6" passive inlet.fine. 8" hole leaves in much more air than two 4" holes and I would consider it overkill. FYI, my air inlet goes through a box I fuilt with a furnace filter in it to keep out dust and insects.

 

[McTavish]

I have two 6" passive intakes, and a 6" fan pulling out and it works fine. For a 4" exhaust, I would use two 4" or one 6" passive inlet.fine. 8" hole leaves in much more air than two 4" holes and I would consider it overkill. FYI, my air inlet goes through a box I fuilt with a furnace filter in it to keep out dust and insects.
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So with my 4inch exhaust, and say a 6inch passive intake like you recommended, would that still create a small amount of negative pressure in the box?

My instinct would say that for negative pressure your passive intake would need to be smaller than the exhaust but everyone including yourself says otherwise.

If the passive intake was smaller and less air could come in than the exhaust fan wants to take out would that not be creating negative pressure and sucking the tent sides in slightly.

I’m sure you’re right as most people on these forums seem to have the same set up you have mentioned but I just don’t get how allowing more air in passively would create the desirable negative pressure that would suck the tent in slightly


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[bartlancertp]

I originally ran 6" in and 6" out, but supposedly the fan moves more air with more air coming in, so I added a second 6" intake. The in line fans usually have a pretty good pull and will create a suction. I feel a strong suction on my door with 2-6's coming in, and 1-6 going out.