Tents and Vents

[idiophonics]

So I am currently growing in a 4x8 grow tent. I have lots of inline fans. My question is should I have the largest CFM fan at the beginning of the run or the end? Currently I have it at the end pulling air out of the tent to the outdoors, but it causes the sides of the tent to pull in as the air pressure is quite a bit lower in the tent than outside. Would I be better off having the largest fan at the beginning pushing fresh air in and the smaller one pulling it out? I also have a large charcoal filter at the beginning of the intake.
Thanks in advance for your input.

 

[az2000]

Would I be better off having the largest fan at the beginning pushing fresh air in and the smaller one pulling it out?

That might create positive pressure in the tent, and cause odors to escape (not through the carbon filter). You want negative pressure. There's nothing wrong with having the tent walls sucked in. You want the air volume to be sufficient to maintain temperature and humidity. If your fan is pulling too hard, you can get a variable speed control. Pushing air in with an intake fan seems unnecessary, unless you have a lot of heat to extract. (Moving too much air will make the carbon filter less effective too. ).

 

[idiophonics]

right now it is a heat issue.

 

[az2000]

PS: I once read that the volume of the tent should be replaced every 5 minutes (if there's no reason to replace more frequently, such as heat). My tent is 4x4' 7'tall. That's 112 cu. ft.

Divide by 5: I need to extract 23 cu. ft per minute.

A clumsy way to measure that: Convert cu ft to gallons (172 gallons in my case).

A large 35(?) gallon trash bag is 1/5th of what I need to move in 1 minute. So, if I place one of those trash bags on the exhaust tube, it should fully inflate in 12 seconds. (I've actually done this.).

But, again, that's minimum. If you have heat to extract, then you need to extract more volume.

I made a custom fan switch based upon temperature. If the temperature in the tent exceeds a whatever I set the control module to, it will bypass the variac speed control, and the fan will go full blast until the temperature drops below the threshold. Then it goes back to the variac speed setting (5-minute total exchange). This way, during lights out, the airflow idles at the bare minimum.

I've got the how-to documented. I should put it on my google drive.

 

[az2000]

right now it is a heat issue.

I would use the smaller inline to help feed the larger inline that's pulling out. You can make it balanced, but you still want negative pressure inside the tent, so everything goes through the carbon filter (doesn't get pushed out the zippers).