How much CFM for a 4x4x6 veg tent?

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NUDLE

New Member
Hey yall I'm putting together a 4x4x6 veg tent with a 480w quantam board. I figure I need around 200 CFM but I'm not quite sure. Any advice is much appreciated. Thanks!
 
Love1Fear

Love1Fear

Well-Known Member
You want your room air exchange to be 3 times per min, your tent is 98 square feet times three is 288 feet per second air movement per minute fan with no 90degree turns or you have to get a stronger fan
 
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NUDLE

New Member
Oh okay I was confused I thought you were supposed to exchange your air once every 3 minutes. I'm currently running a 390 CFM in my 6x6x6 tent I'm going to use for flowering...
 
bk78

bk78

Well-Known Member
My veg room has no exhaust, my flower room exhaust only comes on when it hits a trigger point for heat or humidity (which is pretty minimal)

the master grower above is giving you his opinion which is laughable.
 
NukaKola

NukaKola

Well-Known Member
My 2.5x5 veg tent with ~ 400w has a 6” duct booster fan for exhaust and passive intake. The fan never goes above 30-40%. I don’t run a filter in veg though, only use those for flower.

You definitely don’t need 400CFM for a 4x4 with 480w. It wouldn’t even allow your tent to get up to optimal temps for LED.
 
Cloud Surfer

Cloud Surfer

Member
Not giving advice or my opinion, as I am merely a noob... but I was always under the impression that you only need to exchange the air in the tent once per minute as opposed to 3 times per? Just trying to gather as much info as I can, sorry for hijacking this thread.
 
jondamon

jondamon

Well-Known Member
Cloud Surfer said:
Not giving advice or my opinion, as I am merely a noob... but I was always under the impression that you only need to exchange the air in the tent once per minute as opposed to 3 times per? Just trying to gather as much info as I can, sorry for hijacking this thread.
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The rule of thumb is between 1-3x a minute depending upon other factors such as lighting choice, ambient air etc.

As @bk78 mentioned though everything can change depending upon circumstances and your experience/setup.
 
bk78

bk78

Well-Known Member
What I’d like to know is.... Where did this “you have to clear the air in your room 1-3 times a minute completely” thing come from?

I have never done this in my entire growing embargo.
 
xtsho

xtsho

Well-Known Member
I have a tent basically the same size just 8 inches taller with a 600 watt HPS. When I set it up I started with a 200 cfm fan which was plenty. I have since moved to a 400 cfm fan not because the 200 cfm wasn't enough but because running a larger fan and using a speed controller to run it slower makes it much more quiet. But the 200 cfm is plenty for that size tent. However, I would go with a bigger fan and use a speed controller to turn it down. The difference in cost is not much.
 
Cloud Surfer

Cloud Surfer

Member
bk78 said:
What I’d like to know is.... Where did this “you have to clear the air in your room 1-3 times a minute completely” thing come from?

I have never done this in my entire growing embargo.
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The 1 time per minute was just something that I read, and also advised by the local grow store. I do understand that most of those employees don't know their head from their ass which is why I was just asking in this thread.. again I wasn't trying to suggest anything, just a noob trying to learn. I appreciate your info/experience. :)
 
NukaKola

NukaKola

Well-Known Member
NUDLE said:
Thanks for correcting that info guys. I have one last question.. Is the 390 CFM fan I have in my 6x6x6 flowering tent too much or not enough?
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That should be fine. The only reason I could see you needing more is if you were running open hood HPS lights and were having trouble managing temps.

What are your average temps?

Do you have a dehumidifier as well or are you relying on intake/exhaust fans to control RH?
 
C

CTGrown203

Well-Known Member
A 4 inch fan should be more than enough for a 4x4 that’s 200cfm being moved that’s ur whole tent twice a minute so like somebody said unless ur running open hood hps or growing in like satans attic u should be fine
 
C

CTGrown203

Well-Known Member
I run a 6 inch infinity ac thru a 4x8 and a 5x5 and it’s still not turned up all the way but it’s in a basement
 
N

NUDLE

New Member
NukaKola said:
That should be fine. The only reason I could see you needing more is if you were running open hood HPS lights and were having trouble managing temps.

What are your average temps?

Do you have a dehumidifier as well or are you relying on intake/exhaust fans to control RH?
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Its very very humid where I am (ambient RH is around 70% most of the year) so I run a dehumidifier that also spits out cold air and helps keep my Temps right around 73-75f with an RH of 50%-60%. Im running an HLG 600H (600w) and a 630w BESTVA that puts out alot of heat.. ill upgrade to a 600w QB soon. I haven't been able to get RH much lower than that but I haven't had any problems yet. This is my first run with the new setup I'm about a week from harvest and haven't run into any mold/bud rot problems.
 
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