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Airflow rates for fans - please help

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New Member
Jan 10, 2001
Heya all... I'm currently looking to purchase some high-quality (and expensive) fans for my system. The first priority I have with them is that they be *quiet*.

Therefore, my current plan is to replace my power supply fan with one which is rated to move 27CFM @ 19dBA out of the machine, and have a 9cm fan at the bottom front of the machine pulling in 36CFM @ 23dBA. I also want to place a 6cm 15CFM @ 19dBA fan on top of an ALPHA PAL6035 (interfaced to my Duron 700 with Arctic Silver).

I am wanting to do some experimenting with overclocking, and want to know if this arrangement is going to be inadequate for proper cooling of my system.

Also, is the fact that inflow is 9CFM greater than outflow going to cause many problems? Does it screw with normal operation of the fans?

Okay, I know that the proper way for me to find all this out is just to try it, but these fans (Papst) are expensive, and it's very difficult to get them retail, so I want to try to get it right first time.

Thanks for your help.
'Fraid that you'll need to replace your processor and motherboard for a quiet-running box. Even when not overclocked, Duron's are hot CPU's. They'll self destruct in 14 seconds if no HSF is present.

Seriously, don't even dream of experimenting with OCing with the proposed hardware you write about. In fact, don't think about running the CPU at stock with a such inadequate cooling. If you truly want a quiet machine, you'll need to build a new PC. Unfortunately, the simple truth about cooling is that good cooling of hot processors and mainboards= loud.

I suggest: Don't replace your present PS fan with a quiet one. Add an 80mm 42.5 cfm exhaust fan to the upper rear of your case. Put a 27 cfm 60mm fan on your CPU's HS. If you're gonna try OCing, 27 cfm is NOT enough, period. Replace the 36 cfm 92mm intake fan with a ~44 cfm.

Believe it or not, using the hardware I've suggested STILL isn't adequate! Duron's need a minimum of 50 cfm throughput. And that's at spec!

The nine cfm difference you ask about is quite alright. A bit of overpressure inside cases is a good idea.

If you must have a quiet machine, you'll need a CPU that produces little heat. Duron's and T-Birds are out of the question. Un-overclocked PIIIE's may be OK. With massive HS's that require little airflow.
Yes.... you ´d need higher airflow... But you probably can bear the papst 33cfm fan on the alpha... 15 cfm would be poor performance.. the original sanyo denky 20cfm fan are already silent...

Reading the complete papst datasheet they sent me, i recognized the "N" series of fans, that compared with their older generations of fans with same cfm, are quite quieter... They have a complete solution, even with variofans... 120mmx38mm low speed fans would be a good option with decent airflow and tolerable noise... Check on the net their datasheets and contact them trough e-mail, you may ask some local vendor if he could buy them for you... If you want silent.. Try those bay and slot coolers too, and maybe insulate your case with soundproof material... (hard to find) or go straight to watercooling, self made... It´s quite inexpensive and silent option depending on what you buy...
Hrmm, thanks for the info guys. I've revised my plan of attack, and have now come up with the following:

33CFM 6cm fan @ 43dBA on the Alpha PAL 6035 (I figure that if I insulate the system case against noise well enough, which I plan to do anyway, then the noise will become tolerable.)

55CFM 12cm fan @ 26dBA sucking air in at the bottom front of the case. I will mod the case here to ensure that air can flow in easily.

Stock fan 8cm with my Aopen 300W PSU (these are supposed to be quiet anyway. If it's too loud, then I'll just replace it with a 27CFM.

20CFM 8cm @ 17dBA mounted to the back of the case, *above* the PSU.

So I figure this will give me 55CFM in, and about 47CFM out, creating a little (desired) overpressure.

How does this sound?

Thanks again.
Where can I purchase one of the Papst 33cfm fans mentioned in this thread????????