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Ventilation help - Size of fan?

Odorous

New Member
Hey guys, I understand (for the most part) the fundamentals of ventilation first of all. I simply don't know how big of an inline fan I'll need.

My grow tent is 3x3x6 roughly. I'll be using a 400w hps with enclosed hood with 6" flange. I have 6'' flanges and 4'' flanges in my tent.

Now I already have a 6'' duct booster fan. Last grow, I only used IT to cool the light, didnt do much at all and burnt the shit outta my plants! So I need to buy an inline fan.

On top of that, I want to buy a carbon scrubber as well.

There's a fan/filter combo on HTGSupply.com that is a 4'' both fan and filter(cfm of 170) for only 120!!!! I'd love to buy that but I don't know if I can use it (since my hoods 6''), so should I just

In any case, since I have a duct booster fan:

a)should I isolate my hood and only suck air through it straight from outside the tent and straight out outside the tent (IOW: path: 6" hole in tent --> light ---> fan ---> 6"hole in tent). THEN just use the duct booster fan to power the carbon filter? Is a 6" duct booster fan strong enough to suck through a carbon filter?

b)should I use the duct booster fan and an inline fan together to run both? (IOW: path: carbon filter--> light--> fan--> ductbooster---> 6"hole in tent)



I know there's plenty of ventilation threads on this site (i just looked through like 12 lol) but none of them are helping me answer my specific question. So if someone could please help! thatd be great!! here's a pic of my tent to give you an idea:"

420_0861.jpg


obviously still in veg, but flowering coming soon! hence the question...

THANKS!
 

Hogdady

Plant of the Month: June 2010 - Nug of the Month: July 2010
The idea is to exchange the entire grow space air volume 3-5 times a minute by moving air in and out of the grow chamber.

Your 3x3x6 tent has 54 cubic feet in it. So you need a fan that will move between 162 and 270 cfm.

You don't really need to move air thru the hood unless temps are an issue.

:)
 

Odorous

New Member
hey thanks hogdady!

but check it!

lets say a fan has cfm 170---> how much will that be effected if i put a carbon filter on the end of the ducting?... isnt that going to hold back a lot of ability???

and YES i will DEFINITELY be pullin air through the hood, cuz like i said, i burnt the shit outta the last crop cuz i wasnt pullin ENOUGH through it
 

Hogdady

Plant of the Month: June 2010 - Nug of the Month: July 2010
lets say a fan has cfm 170---> how much will that be effected if i put a carbon filter on the end of the ducting?... isnt that going to hold back a lot of ability???

Absolutely! So you need to oversize your fan a bit to allow for it...:)

and YES i will DEFINITELY be pullin air through the hood, cuz like i said, i burnt the shit outta the last crop cuz i wasnt pullin ENOUGH through it

If you use your inline for this, you will have to push air thru the hood...
 

Odorous

New Member
push?... really??? i thought i should be PULLING the whole way from carbon filter -> to light -> to outside ???...........
 

Hogdady

Plant of the Month: June 2010 - Nug of the Month: July 2010
push?... really??? i thought i should be PULLING the whole way from carbon filter -> to light -> to outside ???...........

look what you just wrote...."carbon filter -> to light"

isn't the air being pushed thru the light?
 

Odorous

New Member
well it would be more like start sucking air in the tent through the filter, then pull it through the light/hood, then pull it outta the tent. the fan would be very near the exhaust...
 

Hogdady

Plant of the Month: June 2010 - Nug of the Month: July 2010
well it would be more like start sucking air in the tent through the filter, then pull it through the light/hood, then pull it outta the tent. the fan would be very near the exhaust...

Bad call. As I said, centrifigul fans push way better than they pull.

Start with a fan/filter combo and push thru the rest of the system. Bear in mind that you will need a good sized intake for the grow space...
 

Odorous

New Member
well the intakes passive... pretty big size "holes", per se, in the bottom of the tent. Sooo youre saying filter --> fan---> light ----> exhaust?
 

Hogdady

Plant of the Month: June 2010 - Nug of the Month: July 2010
well the intakes passive... pretty big size "holes", per se, in the bottom of the tent. Sooo youre saying filter --> fan---> light ----> exhaust?

Yes, but bear in mind that you are using the heated air in the tent to cool the light. If temp @ light is still an issue, you will need a separate fan and ducting pulling cooler air from outside tent to cool light. Good growin' :)
 
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