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A fan through the bottom of my case?

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Nov 16, 2001
U.S. East Coast
I want to cut a hole in the bottom of my case and put my 120mm fan in it as an intake fan. And then I'll build a wooden box for my case to sit on that opens in the rear and for my fan. I'll then block off the front intake of my case all together and exhaust with my rear case fan and PSU. My objective is to quiet the thing down while still getting good air flow. I figure the box will be as long as my case and about 3" high, so the opening in the rear will be about 3" x 7". Any thoughts... good or bad?
Here's a side view drawing. I was thinking about ducting the 120mm to the HSF and then maybe put an 80mm fan blowing on my hard drives. Thanks for your response.

Edit: I have an Antec SX630 mid-tower, fairly hard to cool.
1Time said:
Here's a side view drawing. I was thinking about ducting the 120mm to the HSF and then maybe put an 80mm fan blowing on my hard drives. Thanks for your response.

Yeah, that would work good. I wouldn't make the hassle of ducting it from the way back, I'd just stick the case on 1 inch pegs.
Be sure to leave at least 1 inch breathing space otherwize the 120mm fan(s) will be constricted.
Since my primary goal with this mod is to get the thing quiet and yet still have some decent air flow, my first thought was to have about 65 CFM coming in with the 120mm and about 45 CFM out with the 80mm case fan and the PSU 80mm.

Then, for my 2nd rig for which I'm still buying parts and hope to O/C a bit more, I was thinking of doing this same mod but with two 120mm fans in the bottom with one ducted directly to the HS and a 3rd 120mm as the only exhausting rear case fan besides the PSU fan.

EDIT: The idea with the duct opening only in the rear is to point all the fan noise in the same direction (away from me). I plan on building this duct out of about $10 worth of 1"x4" and 1"x10" pine.
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I can only say that what you're doing is very much like what I have added to my microATX setup.

I too cut a hole in the bottom, added another centimeter to the feet, and the added a 55 cfm 120 mm pabst low-noise cooler.

Just make sure the air you take in from the bottom can actually reach the CPU and PSU properly... in my case my Ti4400 almost blocks the airflow from the bottom because it is so wide.

edit: don't waste your time building the duct below the PC, you wont hear the noise from the above 55cfm 120 mm Pabst. It runs at 26 db. In my case it is ultra quiet, but you might want to give the bottom a layer of magic fleece or noisekiller.

Cheers, Flixotide
Now I'm thinking it might be better to angle the 120mm toward the HS as shown in the attached. This also would make it easier to duct from the 120mm to the HS. Really appreciate all the input. Please feel free to comment further, good or bad. Thanks.


  • sketch.jpg
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I have an 80mm fan angled like that hanging from underneath the hard drives with some zip-ties. It cools my graphics card and provides air to the processor.

My system temps dropped about 2 degrees (my system doesn't run hot anyway, it was just to cool my ram and gpu)

Edit: spelling
It all depends on how you want thinks to look and feel. I personally opted for the bottom fitted fan, because it was easy to implement, and would give me quite a few cfm's at low bel.

Just remember if you mod it the way you sketched it, that you mightn't get a very good result unless you push enough fresh air through your home made duct.

Bottom mounting it would give you direct access to fresh air, the sketched design has a longer and wider air access surface, which wouldn't necessarily be better.

Again, it is as much a case of how much effort you wish to put into it.. I can recommend the bottom mounted design, because it is easy and good.

Cheers, Flixotide
with that case..i think you have 2 80mm fans in the front right? and then 1 more in the back. if you really wanted to, i would put the 120mm fan so that it blows over your video card/cpu. ducting is just a pain in my opinion, because then its hanging there when you open your case.. and after all, the cpu isnt the only thing that gets hot in the case...so put the 120mm on the side, then if you have a extra fan, something like a 92mm or another 80mm, put that at the top, where the space is between the psu and the back of the cdrom drive
Since I'm shooting for a quiet system that air cools well, I'm willing to give up the cooling benefits of having fans in the front, side and top in exchange for less fan noise.

The reason I'm wanting to duct the intake to the HS is to eliminate a need for a fan on the HS and in doing so further reduce the overall noise level. Granted, it may not be worth the hassle, but I'd still like to give it a try... to pump 65 CFM of fresh air to the HS without having to listen to an 80mm HSF.

I like the idea of elevating the case with pegs, and I have no doubt a 26dB 120mm fan in the bottom of my case would be quiet. Thinking about this gave me another idea. I could use 2 by 4's to elevate the case. Cut 2 pieces as long as my case and 2 more about 1 foot long. Then, nail and glue them into a rectangle that would look like a 3 1/2 inch deep picture frame. And then tack some magic fleece across one side as though it were a picture in the frame. Then, lay it down and set my case on top with the front and rear of my case resting on the 1 foot long 2 by 4's. This would leave 2 openings on each side of the case measuring about 2" x 15" for air to get to the 120mm intake fan(s). Seems this would be more quiet than using pegs since the 2 by 4's would act as a sound barrier, and it would be easier and cheaper to make than the wooden duct.

I still like my original wooden duct idea although I might make it a little bigger than I'd first intended to allow for easier air flow. I can't help but think this would be the most quiet option for whatever amount of air my 120mm fan(s) move.

I'll see if I can post some pics maybe this weekend. Thanks again all for your input.
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I like your first idea better simply due to it's simplicity. However one thing you should remember is to add a nice filter, because the first thing I think of is DUST!!! You might add the filter in the end of your wooden construction. That way you will not restrict the air flow all that much because of the larger area.
Right, I'll definitely be using one of these filters I've got laying around. Another thing I neglected to mention is the filter would be easy to maintain since it'll be attached at the rear intake of the wooden duct. Thanks for your comments.