ventilation concerns

[weedmann]

my concern is my intake and exhaust set up.do i have to have the intake alittle bigger then the exhaust.can i have two passive intake to one exhaust.how does that work and whats the best way.right now i have two 4'' hole one for exhaust one for intake but my question is can i have two 4'' inch intake to one 4''exhaust with a intake fan

weedmann Reviewed by weedmann on 04-25-2008. ventilation concerns my concern is my intake and exhaust set up.do i have to have the intake alittle bigger then the exhaust.can i have two passive intake to one exhaust.how does that work and whats the best way.right now i have two 4'' hole one for exhaust one for intake but my question is can i have two 4'' inch intake to one 4''exhaust with a intake fan Rating: 5

[Zeus2007]

I think that you can have the intake hole without a fan, and put an exhaust fan over the exhaust hole- this way when you suck the air out it creates a vacuum in the grow space- which will then suck in fresh air from the intake hole- I "THINK".

[Zeus2007]

:rastasmoke:

[grey1223]

I like two holes for passive intake.

[search1st]

You usually don't need a fan on the intake, so don't bother.

If you feel you NEED an additional fan on the intake (working together with the exhaust fan), when exhausting through a carbon filter (to remove odor) you want the intake fan to be SMALLER (lower cubic feet per minute, CFM) than the exhaust fan. That way all the air leaving the grow chamber will pass thru the filter. Otherwise, you may leak some odor through cracks.

You never want to use only an intake fan for the same reason: the positive air pressure in the chamber may cause the smell to leak out without passing thru the filter. Ideally, your chamber will be NEGATIVELY pressurized, so that if there are any little cracks, clean air from outside the chamber is leaking in (rather than smelly air leaking out).

Also, remember that the air is moving through the 4-inch exhaust fast, and that you may want your passive intake hole to be a little bigger than 4-inches (since the exhaust fan has to work a bit harder to suck the air in through a 4-inch intake than if you had, say a 5- or 6-inch intake).

[daihashi]

You usually don't need a fan on the intake, so don't bother.

Correct, however sometimes you do.

If you feel you NEED an additional fan on the intake (working together with the exhaust fan), when exhausting through a carbon filter (to remove odor) you want the intake fan to be SMALLER (lower cubic feet per minute, CFM) than the exhaust fan. That way all the air leaving the grow chamber will pass thru the filter. Otherwise, you may leak some odor through cracks.

Wrong, you want the pressure to be equalized or for the intake the be passive. In a cabinet enviroment if you have the intake pushing less air than the exhaust and you room is sealed then the intake becomes nothing more than an air flow restriction. It would be better to do without an exhaust in this situation.

Also you shouldn't really have any cracks or anywhere odor can leak out so easily. Duct tape is cheap to buy and easy to use on the inside of a grow cabinet.

You never want to use only an intake fan for the same reason: the positive air pressure in the chamber may cause the smell to leak out without passing thru the filter. Ideally, your chamber will be NEGATIVELY pressurized, so that if there are any little cracks, clean air from outside the chamber is leaking in (rather than smelly air leaking out).

Correct. Don't need to add or argue anything on this one. This paragraph is spot on.

Also, remember that the air is moving through the 4-inch exhaust fast, and that you may want your passive intake hole to be a little bigger than 4-inches (since the exhaust fan has to work a bit harder to suck the air in through a 4-inch intake than if you had, say a 5- or 6-inch intake).

Correct, or as I prefer, make 2 equal size exhaust holes. This will allow you to draw in air from 2 locations instead of one and help to keep the temperature even throughout the entire cabinet. :thumbsup:

[weedmann]

nice:thumbsup:

[daihashi]

It would be better to do without an exhaust in this situation.

This should've read intake, not exhaust. Would be better to do without an intake in this situation.

[search1st]

Wrong, you want the pressure to be equalized or for the intake the be passive. In a cabinet enviroment if you have the intake pushing less air than the exhaust and you room is sealed then the intake becomes nothing more than an air flow restriction. It would be better to do without an exhaust in this situation.

Also you shouldn't really have any cracks or anywhere odor can leak out so easily. Duct tape is cheap to buy and easy to use on the inside of a grow cabinet.

Yeah, what I meant was that the intake fan should be SLIGHTLY smaller compared to the exhaust fan, but of course they can be equal. It's just hard to get them EXACTLY equal since the exhaust fan is loaded with ducting and the filter. If you try to vary the fan speed, the fan speed controller is an expensive item (sometimes more costly than the fan itself). I suppose you could duct some fan air away to vary the CFM of the intake fan.

I just wanted to emphasize that if your intake fan is LARGER than the exhaust fan (after loading) then you'll have positive pressure in the chamber and may have the CHANCE of leaking unfiltered air if your chamber is not absolutely air-tight.

As for cracks and air leaks in the chamber, they could develop over time and may not be revealed by light leaking out.