Combating too much negative pressure in a grow tent

[OldSSSCGuy]

What is the CFM of this exhaust fan? Definitely sounds oversized for the tent.

 

[Bmac1]

Mine is right around 400 cfm. I want to say it was like 386 cfm. Not a huge fan.

 

[indagroove]

What is the CFM of this exhaust fan? Definitely sounds oversized for the tent.

I personally use a 440cfm fan on a speed controller dimmed down to around 75% in a 4'x4'. I know that I could just get a 300-350 cfm fan and not need the speed controller, but in my experience larger fans dimmed down are quieter than smaller fans pulling the same wind at full speed.

 

[Mr. J]

It's once every three minutes not three times a minute. Why do you need to move so much air? Once every 3-5 minutes is sufficient as long as everything else is okay.

 

[indagroove]

It's once every three minutes not three times a minute. Why do you need to move so much air? Once every 3-5 minutes is sufficient as long as everything else is okay.

I aim for twice a minute, and I also try to account for resistance loss from things like ducting, filters and such. Just because you run a fan at 350cfm, doesn't mean it's gonna move 350fcm of air out of your tent. I used to move less air, and fungal issues were much more challenging. After I starting moving more air a lot of those issues self-resolved.

 

[Bmac1]

I have my fan dialed down as far as the speed controller would allow. I assume its about 25% of full blast. I need constant flow through the filter due to living in a high density situation.

 

[mtntrogger]

Not what you want to hear, but I had the same problem for years. Tried all kinds of stuff to combat the neg pressure ! Shit sucks, stretches out the tent corners causing light leaks and all kinds of issues.
I recently switched to a led, and I have to say they are the shit !! With my led at full power (not dimmed) I can run my exhaust fan on the lowest possible setting (which makes zero noise) and my temps dont get over 70... with the lights on ! Absolutely no negative pressure. Leds are the game changer for sure. Not cheap, but worth every penny. Seriously, zero noise growing

 

[Freestyle72]

Negative pressure is a good thing as far as containing smell, no doubts there. My problem is that I am having too much negative pressure. Almost to the point where my 5x5 tent is acting more like a 3.5 x 3.5 with how much the sides suck in. I am losing too much floor space.

I have a 6in fan pulling air out of the tent. It is plugged into a speed controller and on the lowest setting. Intake is passive through 1 - 6 in ducting. Another 6 inch ducting intake would be advised, this I know but even with that, the tent still looks like its about to be sucked off the frame and through the fan.

I also want to put a couple of those clip on, oscillating fans in there but there is no way they would work in the corner with how much the sides are sucked in.

I could build something from 2x2 etc but I like the convenience of tents. I just need to get some floor space back as I am downsizing from 5x5 to 2 - 4x4.

Gorilla sells a High CFM pole brace kit (https://www.gorillagrowtent.com/products/grow-tent-cfm-kit?variant=32758937610)

This would be great but of course I cant find a 4x4 kit for the life of me. There has to be other ways to get to this solution. Tent poles are not hard to find but these plastic clips would be a great find as I am sure they are available without a Gorilla logo and a lesser price.

Adding a duct fan may also be in the cards for intake but I would like to get 2 of these brace kits.

Anyone have any ideas?

I would drill a hole the size of my uprights in each end of a 2x2 and then pass the upright through so there's cross bares stopping the tent from coming in.