Understanding air flow

apollonio · May 2, 2010

First, thanks for this thread hoosierdaddy! Lots of helpfull tips that i've used in past grows... thanks for the contributions to redgreenery thread too, that was quite a read! But i have a hard time undestanding all of the information there.

I have a question about a setup i'm working on.. it is based on Anti's MicroStealth Cab, i don't know if you have seen it before Link to the page with the airflow system, see post #39.

In his design, he uses two chambers with the same size. In my design, the veg chamber is ~12"x31" (30x80cm) and the flower chamber is ~16"x31" (40x80cm). I was wondering if one of the chambers would get more airflow then the other? I think it will but i can't figure out which one and what should i do to overcome this issue...

If you can, help me out on this one! Thanks for your time!

:tiphat:

hoosierdaddy · May 5, 2010

Hey, apollonio...thanks much for the kind words. I can only hope that I have helped a little bit.

Anti is pulling the air from the two separate chambers and into a single exhaust. This is fine do to, as long as the fan doing the work has enough power to satisfy the dual chamber air flow.
Now, the sizes of the chambers really don't matter much at all. We could have a box the size of one side of yours, and the other side as large as a sports stadium and there wouldn't be one bit of difference in the amount of air flow in the small side of the cab and the stadium sized side.
The key is the size of the entry and exit ports. That controls most all of the physical effects of air flow. And as long as you have properly sized the intakes, the fan will pull virtually identical amounts of air from each side, no matter if they differ in size.
If you make one sides intake smaller, it will cause resistance and there will be more air coming through the other chamber, but if they are identical in size, they air flow will be virtually equal.

Hope that helped!

apollonio · May 5, 2010

Hey man! Thanks so much for the answer! It indeed helped...

Since i'm going to use a separate air system for the lights (with a glass shield), i think i can use a fan with 90 CFM for both chambers. It is a 12cm (almost 5 inches) axial fan. I'm sizing the main intake hole with 300 square centimeters... wich is more then twice the exaust area size. But in my plans, each chamber has 150 square centimeters, so making a total of 300 square centimeters... is that ok? Or should i size each chamber with a total of 300 square cm?

Thanks again!

hoosierdaddy · May 5, 2010

Your exhaust has a flow of 113 sqCM, so yes you will be fine as wine with 150 each side.
90 cfm isn't much air movement, but if you are cool toobing the lights, it may well work out fine. I suggest a $27 duct booster for cooling lights, and 6" is far better than 4" no matter how you shake it out.

If this is your first real attempt at doing the thing since your membership here, I am very excited to see this happen for you! Don't hesitate to holler if you need any help.

real ting · May 16, 2010

Hey hoosier, I remember you saying in one of your threads (ac box i think) that you liked using insulated foam board for ac boxes and other air related box needs. I think the brand was dow corning supertuff r. I need to make a couple of boxes that accept different exhaust ducts from around the room, ac boxes, and I also wanted to build some L shaped light traps. In my state they dont sell the supertuff R rigid insulation, but you can get R3 rating r-max 1/2 foam insulation board w/ foil on one side. Will this work the same for these sorts of applications? Is heat a problem for these types of insulations?

If it would work, what would you suggest to hold it together and into shape?
Just tape it up with duct tape or is there a more sophisticated method?

Thanks.

apollonio · May 16, 2010

Thanks for the help hoosierdaddy! I resized everything since I changed the extraction fan for a 6"... I think it will work better indeed!

All the best!

hoosierdaddy · May 16, 2010

Hope it works out for you, apollonio.

real ting, If all you can get is single sided aluminized sheet, it will probably be ok. The Dow board is rated for around 140degF, and the board you can get should also have a similar rating. I would keep the metalized side towards the heat...or you could double and turn one around.
Use aluminum tape. It can be very expensive depending on where you buy it, but it can be found for cheap. Shop for it, and use it early and often.
Only use duct tape where there is no heat involved, and only use Gorilla brand tape.
There is no substitute.

Bazarocka · May 22, 2010

OK

OK

Outstanding.........I had to think twice, but hell Im pushing that dreaded _____ year :ying:

FrijolElVerde · Jun 10, 2010

Amigo, Muchas gracias for your Very Good Info:thank you
How would one (hypothetically speaking, of course) setup the venting in a house using an evaporative swamp cooler? The whole interior of the house and box is under slight pressure and air would try to push out thru the box fan and exhaust. Each room of the house would have a window slightly open to allow cooling in all rooms. The evap cooler has off-low-hi settings.
Crazy, No? Too many CFMs out of the box and the livingroom gets hot!
If you don't want to think about this it's OK!! Cause it's makin' me loco!!

jakeh · Jul 19, 2010

Hoosierdaddy,
This is exactly the thread and information I needed. I still have some questions though. Picture a right angle triangle like you would get under a stair case "l__". I have a roughly 16 cubic foot square (43"wide x50" long x60"high). My plan is to completely seal the room with spray foam (with the exception for intake and exhaust). Along the 50" long section there are 2 walls like this "l l" with a 6" gap between the walls for plumbing from upstairs to downstairs. My idea was:
1. put a carbon scrubber at the top of 16 cubic foot growing area to pull the heat from either a 430 watt son t agro or a 600 watt hps that will be hung vertically with no cool tube.
2. attach a 6" diameter length of pvc to the scrubber and send it up through the 6" gap between the walls "l l" up and into the attic.
3. Add an inline fan in the attic at the top to pull the filtered air into the attic.
4. seal the 6" gap between the walls except for the bottom 12" for a passive air intake.

Do you think this should adequately cool the space?
Any suggestions?

thanks,
jake

calstar · Aug 4, 2010

Thanks, this really answered a lot of questions for me.

WESTCRAZY1 · Dec 13, 2010

Hope i can get some answers --

My grow box is 28in Height, 23in Length, 16in Deep/wide. Im trying to fit a 250w hps (cool tube) in there and make it work. So far my ventalations are as followed ---

1. 5" intake fan
2. 5" exhaust fan
3. 4" circulating fan

Do i need anymore intake/exhaust fan's to bring my temp to level? Or am i better off with a 150w hps? If 150w hps is better for my set-up, will it work with the current vent set up that i mention above? Thanks.

Critter · Dec 13, 2010

^ You need a bigger grow space.

kjz71521 · Sep 14, 2011

Nice post on airflow.. Watchin.

Rolldaddy · Nov 12, 2012

veclo · Jan 22, 2013

Great post, very informative.

One question though.

Will the use of a PVC elbow like this

serving as a light trap on my intake holes reduce the airflow by a lot?

To put things into perspective, I use a 4'' computer fan as exhaust in my cabinet, now that equals to 12.56 sq in, i was planning to put 2 12.56 holes for the passive intake and mount the olbows onto them.

Do i need to make bigger holes, compensating for the loss of airflow because of the elbow or will I be ok with that setup?

messn'n'gommin' · Jan 22, 2013

As long as it's roughly 2/1 ratio (intake to exhaust), you should be ok. The bends in 4" elbows won't lose enough to resistance to greatly affect airflow.

This link is another construction option to consider:
"Cheap easy light trap for venting." By Ichabod Crane
https://www.icmag.com/ic/showthread.php?t=224159

veclo · Jan 22, 2013

Great, thanks for clearing that up

Dr Watt · Jul 3, 2017

Revisit. Minimum cfm. I've downsized on fans size - with the right configuration you don't need that airflow. Heat rises a lot and head room over lights is needed for min cfm. Exhausting from the ceiling is very effective. High up is good but ceiling means all your hole is at maximum height (cheese smile). Less ducting best down to 2ft i'd reckon 10ft would still work if straight etc (5' edit 38w+ which is larger than I've seen lately) computer fan w/ 6''duct ~ 100 cfm). Finally, the air has to pass through your plants, leaks close to your exhaust will destroy the airflow.

Take my grow - 10 sq ft, 570 watts (one 250 ballast is (edit globe is pulling )320watts - generic yellow globe anyway (edit which turned out superior to White mh for mh type bud then >> hps to finish imo atm. {yes I own a meter whereby you can actually know what amps, volts, watts, power factor is being generated at the wall by these globes / devices), lightweight batwing reflector, closet (8ft high), the ballast is up high, Can 33 (quite big Carbon Filter), 5'' Computer Fan > 8" Mixvent (summer - closet shelving ruining height factor), 2.5' x 6'' ducting with 2x90 degree bends - (it's winter and I'm exhausting into a nearby room - hated wasting that heat) AND I Have this fan only running 3min/on 5min/off on thermonstat (winter). To give you the figure I've got about 7c on ambient with the fan running 100%. I sealed up the gaps from 4ft up so air does pull from furthest distance (the floor and up to 4ft) - and as stated on this thread aim for 2 x fan diameter for your intake.

MitchelWitting · Aug 25, 2021

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Understanding air flow

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