So I am designing a small dresser grow box. I plan on using CFLs for veging, then switching to HPS with CFLs to supplement durring flowering. To work out the ventilation I went to the GrowFAQ: GROWFAQ

There, Using the formulas in the post, I have an inside temp of 76 degrees, and I plan on at max using 200 watts (150 for hps, 23 for cfls, and a few extra for buffers (running fans and whatnot)). Which means I need around 125 CFM moving. I got two of these:
Cooler Master 120x25mm Dual Ball Silent Fan (Y720CCD-25K1-GP) - 109.6CFM - FrozenCPU.com

Both are rated at 110 CFM, so I hoped to dial them down a bit and cut back on sound. I use passive intake on the bottom that goes through 90 degree angle in order to work as a light trap. When I turned it on to get a temp reading, with both fans working at max cfm, I was still getting temps around 85 degrees inside when the room is about 70 degrees. This poses a problem because I was only using 100 watts of CFLs. So I cut more holes in the bottom to create larger passive intakes, thinking this was the problem. It hasn't solved it yet. Temps are still 15 degrees above the room temps with only 100 watts of CFLs in there. How can I cut the temps down?

I can't make the intakes any larger without breaking the light trap, but do you think this is the problem? and if so how do I fix it?

Do I need higher rated fans?

Please help guys. Look over the pics, I know they arn't the best but ask if it isn't clear. Thanks

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anyone ..... please .....

Get a TD-mixvent duct fan made by S&P. I got the smallest one rated at 103CFM. Google it. I just solved my heat issue with it after three tries. My cabinet is slightly bigger than yours and I have about the same lights (150watt HPS and 4 23 watt flours). It's also pretty quiet. When you hook up those computer fans to ductwork with poor intake they don't move much air at all. Put your hand back there and see for yourself. I bet you are not getting anywhere close to 50CFM with both of them. The MIXVENT sucks air pretty good when used inline and I have shitty intake vents. Keeping my temps around 80 with all the lights going. I have found that ventilation is the hardest part of stealth cabinet growing. Big fans are too noisy and little ones don't move air. Stay away from those suncourt inline fans.

A cheaper solution might be to add another computer fan at the intake, But that's three fans making noise and it sounds like stealth is a priority for you. Me too!

I've heard good things about those fans, the only issue that I have is space. As you can see in the pics I don't have much of it. How big are they? and if you don't mind me asking, what is the size and dimensions of the one you have? The outside of my box is only 16inches x 15 inches, and the inside is less than that, will it be able to fit in there? In addition, my height is only about 3.5 feet high, so all of the space that the fan makes will take away from space that I have for lights and plants. I'd rather get one of these than fry the plants, for sure, but I'm just concerned about it fitting in there.

I liked the idea of the computer fans, for one because they could lie flush with the wall, so it didn't affect the space inside the cab, and for two because they can be dialed and messed with rather easily. I might try just taking away the ducting from the fans, and putting the computer fans directly against the wall and pushing straight out. I'd have to work on the light issue though, so I'm not too sure what I'll do.

The only other thought is if I could somehow wire one of those TD Mixvent fans so that it opperates outside of the cab and looks like something else, but this isn't really what I would prefer to do.

Thanks for the help.

dimensions can be found at HVACquick.com I cut off the electric box on the side and the mount so it would fit through my 6 inch vent hole. I have mine hanging out the back into the attic. I'm fortunate enough to have my cabinet against a wall that allows me to vent to the attic. With all that stuff cut off it is about 5 1/2 inches diameter and about 9inches long(guessing). You could probably cut off 2 inches from the length if you are handy with a saw. If you got this I would put it outside the grow box, but it can also fit inside I'm sure. I just got fed up with the computer fan thing early on as they did not move even enough air for my seedling lights. So I started in with the small inline duct fans. The MIXVENT was my third and final try. Hope you don't waste as much money as I did. They say to go big as you can always dial a fan down, but I did not listen. Please post what you decided and how it worked out.

Maybe something like this would help your situation? I use a bucket with gel ice packs to lower my 5'x5' closet space by a couple of degrees for several hours. Helps when you don't have too many options. Especially if your dropping from 91 to 88 degrees

Interesting idea Puff, and I'll keep it in mind as a last resort, but not exactly my first choice, no offense.

I ordered an S&P TD-125 today. I heard alot of hype about it, and to be honest with you, I'm a little disapointed. It moves some serious air, that's for sure, and I'm testing it as we speak for the heat problems. I'm sure I won'nt have any more heat issues now, but it isn't as quiet as I hoped. I got a rheostat for it, to control the speed hoping that it would knock down the sound if I knocked down the CFM, but no luck. With the Rheostat on, the lower I dial it down, the louder the buzzing/humming noise gets. Right now it sounds and looks like a jet engine, going to have to try a few things out.

I could not find any fans for sale that moved air well that were made to be silent like the S&P Mixvent. I have the smaller version and it is the stealthiest I have achieved after trying two other fans. I think it is impossible to move the amount of air you need and be silent. If you got 5 computer fans going it would maybe keep up with the heat, but it would probably be just as loud. The air movement creates most of the sound. So if you are looking for ultra stealth you may need to scale back the grow and use CFL only and go back to the computer fans. Problem with that is that when it comes time to control the smell, you are going to have a hard time getting those fans to blow through a carbon filter.

Sounds like you want to have people in the same room and not hear anything. I think they are pretty quiet but mine is hanging out the back into the attic. Can you run a vent to the attic? If so problem solved as you can put the blower in the attic and connect it to the box with insulated flexible ducting which absorbs wind noise

I may end up doing just that, but we'll see. I'd like to keep it all in the box for now.

And the fan it self is wonderful, don't get me wrong. It moves a phenominal amount of air and is fairly quiet. My sound problems, however arn't from rushing air. It's from the fan itself. It's making a fairly loud buzzing/humming sound that can be heard outside of the box. You don't have that problem?