CFM 1.2x1.2x 2

Would you know anything about a 4x4x6 grow tent CFM needed with carbon filter about 4m ducting and one bend? I have 240CFM in-line under LED but I’m thinking it’s to much, my wall aren’t pulling in and only one passive vent is open. two fans running, one hanging and the other from the ground in opposite sides from each other. So carbon in far corner and the other two isolation fan in their each.
is it over kill should I turn down to 150CfM
Hope you can help. And thank for taking the time to reply and care. All the best stay safe to you and all you know.

If you’re not bothered about 3x exchanges of air per minute you can go down to as low as 96CFM as long as your temps are ok doing this.

1 exchange 96CFM
2 exchanges 192CFM
3 exchanges 288CFM

CK?1 said:

I’m thinking it’s to much, my wall aren’t pulling in and only one passive vent is open.

Click to expand...

So are you using 2 fans, one as intake and one as exhaust (push - pull setup)?

To achieve negative pressure you want the exhaust to have a little more CFM than the intake if using a push pull setup. Most just use a pull setup with the passive intakes.

I am confused on how you are setup, the one fan as an exhaust with one passive intake open should cause some negative pressure provided the ducting hasn't restricted the flow and killed the CFM.

Any pictures you can provide of your setup will help us see potential problems. Include images of the ducting as well. Using accordion duct and having it not straight causes a lot of CFM loss.

Renfro said:

So are you using 2 fans, one as intake and one as exhaust (push - pull setup)?

To achieve negative pressure you want the exhaust to have a little more CFM than the intake if using a push pull setup. Most just use a pull setup with the passive intakes.

I am confused on how you are setup, the one fan as an exhaust with one passive intake open should cause some negative pressure provided the ducting hasn't restricted the flow and killed the CFM.

Click to expand...

Hi Renfo
Thanks for hitting me up and showing interest in helping.
so I’ll better explain.
passive intake Budbox tent two vents open, no pulling I only have two oscillating fans desk top fans blowing air in side the tent, they sit on opposite sides of each other. Then my carbon filter running straight to my in-line and then about 4 meters ducting with one half bend. What I have noticed though, is it’s raining her in Cape Town and my humidity is hitting 50 and like 46 with humidifier. So im also thinking I’m venting to much but my rents walls don’t pull in at at all temps stay around 26 degrees in the room I’m passively intaking from.
some pics below. Or I’ll post some pictures now. Again thanks for the reply stay safe and blessed my man. Can’t wait to hear your reply.

jondamon said:

If you’re not bothered about 3x exchanges of air per minute you can go down to as low as 96CFM as long as your temps are ok doing this.

1 exchange 96CFM
2 exchanges 192CFM
3 exchanges 288CFM

Click to expand...

Hi Jondaman.
Thanks for the help. I’d anything I think you’ve given me more food for the thought now, that’s never bothered me I thought to let it. Ive justupgrade to this size tent from a 1meter so things as usual I over think things in my grow room. But you’ll see in my comment below about the low humidity, weird.
im going to ate the fan to its lower setting and see its lower is 140cfm

You’ll see the carbon in the corner the one fan hanging by the lights and the small one in the corner.
your thoughts please guys.

CK?1 said:

Hi Renfo
Thanks for hitting me up and showing interest in helping.
so I’ll better explain.
passive intake Budbox tent two vents open, no pulling I only have two oscillating fans desk top fans blowing air in side the tent, they sit on opposite sides of each other. Then my carbon filter running straight to my in-line and then about 4 meters ducting with one half bend. What I have noticed though, is it’s raining her in Cape Town and my humidity is hitting 50 and like 46 with humidifier. So im also thinking I’m venting to much but my rents walls don’t pull in at at all temps stay around 26 degrees in the room I’m passively intaking from.
some pics below. Or I’ll post some pictures now. Again thanks for the reply stay safe and blessed my man. Can’t wait to hear your reply.

Click to expand...

Also I do have a heater dry air blowing with a Thermo in the tent so if temp drops to low air heating blows close to open vents, once temp is up, which takes about 60sec the heater switched off and so on, the heat stays in the tent for about 2min and then Thermo kicks heater on again blowing warm air into tent. The little heater is outside the tent just to be clear and blows into the open vent. Can’t wait for your guys thoughts.

What do your temps drop to when they go low?

anything above 18C is fine.

what do you think is wrong with your humidity?

I see 61% on the gauge at the surface of the medium??

that’s ok.

your setup is configured correctly as far as I can see. Filter then fan, fan blowing out of the tent.

basic air exchange needs have extra requirements with long ducting and bends.

so basically your tent 4x4x6=96CF

96 equals one air exchange. But we need to add on your ducting, your bend, and your filter.

filter = 20% of 96CF = 19.2CF
bend = 10% of 96CF = 9.6CF
4m Ducting = 10% of 96CF = 9.6CF
19.2+9.6+9.6= 38.4CF extra for your room.

96+38.4=134.4CFM for one exchange per minute.

Other than that I think you’re setup pretty well.

Ahhh your a top man!! Live and Love my garden and gardening mate. Never a dull moment. Yeah temps don’t go blow 18 but I have the heater at the tent vent to blow in warm air to get to 18. Every night after nights out I set the Thermo to turn on if they drop 18. That take like 20sec and it’s at 18 19
Thanks for the chat the time and the sums which I’ll use again whe I go bigger. I think I’ll turn my exhaust fan down to 140 and see what happens. I’ll keep you posted just for the FYI.
you have a great one and thanks for commenting such nice words about my set up, always good to hear from other growers, we know the time love and effort we put in to them.