Why not just use the CPU fan?

This PC project was (is) a headless Linux file/print/web/mtdaapd(iTunes music) server. It would be on all of the time, and the processor demand would be rather low. I wanted it to be as quiet and efficient as possible. I realized that my system wasn't the best path for efficiency, but the budget was $0, and I had to work with what I had. Rather than have the little cheap CPU fan whirring away on my PIII 800 MHz processor 24/7, I decided to see what other cheap/free options I could come up with.

First, I tried just removing the fan and seeing how hot the standard little heat-sink became. It got hotter quicker than I expected, just on boot-up. Boot-up may involve more processor use than this server would usually see in operation, but rebooting would happen occasionally, and I didn't want to fry anything.

I considered other options like a much larger heat-sink, but those involve money. Then I got to thinking; I already had a source of air movement right there in the case: The power supply fan. I just had to harness it.

First I needed some things

Tools and supplies needed:

Open it up

The open case, with the power-supply vents being shown, as well as the heat sink right below that
Open case, fan removed.

Open up the case, and see what things look like. In my case, you can see I had two vent locations for the power supply, and just below, the amazing Pentium III 800 chip and heat-sink. As long as nothing major is between the processor and the power supply vents, building a duct shouldn't be too hard. If you have something there, then you may have to be more creative. As you can see, I have pretty clear access.

Use your brains

I sketched the design on some of the manilla folder, complete with measurments.
Sketch it out.
I traced everything out onto the manilla folder, to prepare for cutting and folding
Convert 3D to flat.

Then it's time to measure distances, sketch a drawing, and figure out dimensions. I'm sure you could use a CAD program for this. I used some scrap manilla folder and a pen. Don't forget to allow some way to attach the duct to the power supply, etc. I left some tabs on the edges, so that I could use tape. Take your time on the design, since you may not realize that your dimensions are off until you've spent a lot of time on the following steps. Measure once, cut twice, and all of that.

Once you have a 3D drawing of your design, you have to convert that into a flat shape that can be cut out, bent, folded, and taped into the finished product. It helps to have a general idea of how boxes are put together. Go, look at a box. Then use the powers of your mind to convert 3D into 2D. Trace the 2D shape carefully onto one of your manilla folders. When you're sure you didn't mess this step up either, cut it out.

Tab "A" goes in Slot "B"

Then I folded the duct into shape.
All taped together.
And now it's taped up.
The other side.

Once it's cut out, fold it on the lines. It helps to roll over the fold lines firmly with a ball-point pen, to flatten it a little and help it to fold more easily and accurately. If everything seems to come together as it should, apply some tape to hold it for a test-fit in the PC case. It should fit in as you planned, without any big gaps to leak air. Any large gaps will need to be taken care of, to maximize air flow through the heat sink.

Finalize the install, by using lots of tape to hold it firmly in place. You don't want it to fall off without you knowing about it. Good way to toast your processor. You might even consider using something more reliable than adhesive tape, like glue, or small magnets. Tape has held up for me for over a year now though.

Results

The duct is now taped in place.
Stick it in there good.

Well, the only thing left then is to test it. I just fired it up with a finger on the heat sink to monitor temperatures. I noticed very little heat, compared to a lot of heat with only the heat sink, and no fan. Any heat that built up while the machine was booting up quickly went away when it returned to a low-demand state. It does what I need it to. I'm not sure I would use this on a gaming system, or other high-performance application, but it does fine for my home server.

You'll notice that I have a flap of folder going over the entire heat sink. This is because it isn't good enough to just pass air through the last 1/3 of the fins. You want the air to travel through the whole heat-sink, removing heat as it goes. The flap on top makes the air do just that. If the sides were open, they would have flaps, too; they are mostly solid though.

Updates

12-20-08 - It's still in there, still working, after about a year.

Feel free to email me if you have any questions or comments about this project.