Tutorial Ventilation 101

[Mr Blah]

I got a 12" exhaust fan (969cfm) exhausting a 6.5x6.5x6.5 tent (275cubic ft).
My goal is to exhaust it three times a min. How big of an passive inlet opening would I need? I would like to have 2.
I think it would be one 15" hole square going by the first page of this thread.

 

[Mr Blah]

five days...nobody knows that number off the top of there head?

 

[Kozmo]

There's a formula. I'm sure if you dig you'll find it. Good thing is, is that you have all the variables.

 

[beta]

Your intake should be at least 2-4x the size of your exhaust, the bigger the better. You can always turn your fan down, but you can't pull air any faster than your intake will allow.

 

[Snook]

I got a 12" exhaust fan (969cfm) exhausting a 6.5x6.5x6.5 tent (275cubic ft).
My goal is to exhaust it three times a min. How big of an passive inlet opening would I need? I would like to have 2.
I think it would be one 15" hole square going by the first page of this thread.

Hi Blah ... I remember and use 2.5x the size of the exhaust... so 30 sq inches. 2, 15"s or 30 1, inch that would be 2, 15"holes. why you want to move that much air? not say its wrong but I might learn something..

 

[GoneP]

So im doing my first run in a new room and i'm running into problems trying to dial the environment due to low temps. its an insulated room inside a non insulated garage. room is about 320 cubic feet, with a 6 inch 440 cfm inline for exhaust, insulated ducting, aircooled 1000w magnum xxxl, glass cover on. passive intake vent.

lights on temps are at 73 degrees, but dips to 70. lights off temps have gone as low as 58, too cold for the first week of flower. the exhaust fan came with a built in speed controller, which i have set to lowest speed but it's still drawing in too much cold air from the passive intake vent, which is appropriately sized.

how can i resolve the cooler temps during lights on? would removing the glass cover and runnin bare hood do the trick? are there any fan controllers out there that will allow me to lower the speed of the inline more?

 

[Mr. Miyagi]

LMAO, I wish I had your problems GoneP lol..

58*F is bit too low, a c02 burner will raise temps a lil bit, a dehuey even more. Bare bulbing will also work. Yes, there are other controllers out there that can slow the speed of the fan, you can also make one (if you're tech savvy), OR you could simply attach a duct damper (which I've done several times to slow the exhaust of air from one space to compensate for exhausting air of another.)

 

[GoneP]

i ended up removing the glass cover and the temp o s holding steady at 77 degrees, thanks Myagi, i almost hesitated to take the thing off, bit now im glad im did. The plants had an almost instantainious reaction to it.

 

[GoneP]

Dont know why the sad face popped up, must've done it by by accident, pretty baked off some glue right now. gonna put the glads by on once buds start forming.

 

[DoubleTripleOG]

Hi Blah ... I remember and use 2.5x the size of the exhaust... so 30 sq inches. 2, 15"s or 30 1, inch that would be 2, 15"holes. why you want to move that much air? not say its wrong but I might learn something..

***FIRST PAGE OF THIS THREAD****
2, 15" holes is a lot more area than 30, 1" holes. Area of a circle is 3.14(Pi) x (r)squared. So 3.14(7.5x7.5)= 176.625 square inches for a single 15" hole. 353.25 square inches for 2-15" holes. 30, 1 inch holes would be 3.14(.5x.5)=.785, then 30 x .785= 23.55. Big difference.

 

[Rox]

So im doing my first run in a new room and i'm running into problems trying to dial the environment due to low temps. its an insulated room inside a non insulated garage. room is about 320 cubic feet, with a 6 inch 440 cfm inline for exhaust, insulated ducting, aircooled 1000w magnum xxxl, glass cover on. passive intake vent.

lights on temps are at 73 degrees, but dips to 70. lights off temps have gone as low as 58, too cold for the first week of flower. the exhaust fan came with a built in speed controller, which i have set to lowest speed but it's still drawing in too much cold air from the passive intake vent, which is appropriately sized.

how can i resolve the cooler temps during lights on? would removing the glass cover and runnin bare hood do the trick? are there any fan controllers out there that will allow me to lower the speed of the inline more?

Heat the air coming in or add tube heaters or oil radiators

 

[Funkamongus]

Damn. I used to be smart. Now? I'm baffled by these graphs and numbers as if I'm alien to the concepts. I don't think it's the info displayed, I think my brain just doesn't want to do the math.... I wish someone could lay it out for me in English.

 

[RiddleMeThis]

So the OP suggests .2 to 1 air changes per minute, or between 1 minute per air change to 5 minutes. Right?
I am reading about guys exchanging their air 3 or more times per minute, and seem to be doing just fine...

Just trying to figure out if I should go with the 8" hyper fan vs the 6" for my 4x4 tents with 1000w air cooled reflectors. The 6" will allow a maximum of 1.7 air changes per minute based on mfg specs with phresh filter. The 8" would allow significantly more changes per minute but I believe the lowest speed will still be over 1 change per minute

 

[Granger2]

The more fresh [conditioned] air the better. If you're hoping to control temps, lots of air exchanges are best. I'd go with the larger fan and use a speed controller if needed at times. Good luck. -granger

 

[oti$]

Granger's advice is spot on, and I'll second at least 2x air exchange/ min. I'm able to keep Temps more or less with in a few degrees of the ambient Temps of the rest of the house this way.

 

[RiddleMeThis]

Awesome thanks guys. 8" hyper will give me between 1 and 3 acpm, should be perfect

 

[JollyGGiant]

Ventilation for a 5' x 5' tent

Ventilation for a 5' x 5' tent

Wanting some help double checking ventilation of my tent. I have a 5' x 5' x 10' tent = 250 cuft. I bought a 6" HyperFan Stealth (315 cfm rating) and 6" x 24" Phresh carbon filter (550 cfm rating). Total length of ducting will be @ 10' or less with (3) 90's. Is this overkill for this size tent? Should I return the 6" stuff and go with 4" instead? Trying to firm this up before I pull the trigger on drilling a 6" hole thought the side of my house. Thanks in advance for any advice

 

[JollyGGiant]

Duh, I forgot to give you the heat inputs. I will be running a Spydrx Plus 680 watt LED. Thanks

 

[Granger2]

One fan will not be too much. If you are only trying to maintain fresh air [with CO2] it should do the job. If you want cooling, I'd get another fan and filter like the one you have. Good luck. -granger

 

[Centrum]

nvm