size of passive intake

BROMAN

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I've heard it said that the size of ones passive intake should be double that of the exhaust so as not to stress the fans motor. Does this ring true with experienced growers? I'm thinking 6" exhaust and 4" intake.
 
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IME, you want your intakes larger than your exhaust. A 4" intake and a 6" exhaust IS going to tax your fan unless you have it on a controller and dialed down. The 6" will only be capable of exhausting as much as the 4" can let in.
 

Dman1234

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make an intake in a way that it can be enlarged, this will allow you to try a 4inch and make it bigger if needed, what i have had to do is simply go by temp, if 4 inch hole and temps are still hi, enlarge it until temps drop. jmo
 

pcduck

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make an intake in a way that it can be enlarged, this will allow you to try a 4inch and make it bigger if needed, what i have had to do is simply go by temp, if 4 inch hole and temps are still hi, enlarge it until temps drop. jmo
And/or you lose negative pressure inside the grow room
 
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I have way more square inches of inlet than I have exhaust and still have no problems with negative pressure in my space.

Keep in mind that a 6" hole is over twice as large as a 4" hole--with a 4" inlet and a 6" exhaust you pulling air through a hole that is 28 sq inches and only have an inlet of 12-1/2 sq inches.
 

Niblixdark

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So what if if exhaust is 6" and you have a passive 4" as well as another ceiling exhaust but for emergency so its passive as well unless its on but I attached it to the side of the grow room, but my room is a room within a room, basically a bedroom but with a floating wall I built. the only true intake in my room is a furnace vent its, 6"

my temps get up to 30, most stay around 25-28.5c 1000watt hid and am about to add another too !!! so I think I will be running into problems in the near future, its a new setup so, I have allot of ironing to do yet !

<----vent>hose>inlinefan>hose>aircooledlight>hose>can filter<-----6" <----- 4" air intake x2, 1 passive or manual <------ 6" air intake passive or manual
 

BROMAN

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thanks for the responses. i've gone with a 4"x14" wall vent at the bottom of the closet door along w/ a 3" hole for the extension cord. from what im reading that should be enough.
 

Hackerman

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Somehow, that doesn't sound very big.

The tent I have has 3 vents that size and if I close 2 of them, the tent sucks itself inside out.

All depends on exhaust fan too but I would put in as big an intake as you can right now. It can never be too much but it it often not enough.

Plus, are you going to put something over the vent to block the light? That will probably impede air flow some as well.

I don't know. Just seemed small to me.
 

DrFever

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I always run two 4" intakes and two 4" exhaust
 

BROMAN

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thanks Hackerman. I figure my intake is double the size of the exhaust and then some. if necessary I will definitely cut another hole. also the closets not as airtight as a tent. I'm not worried about the light because of the way I'm sectioning off the closet for flower.
 

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