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quick question about case fans

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November 15, 2007 11:07:49 PM

should you have a stronger intake fan or a stronger exhaust fan.
November 15, 2007 11:09:14 PM

It has to do with positive and negative pressure.

Positive pressure will result in air being forced out of all the slots in the PC diminishing dust buildup.

Negative pressure has an opposite effect.

I prefer negative because unless you have a perfectly designed positive pressure system it can lead to air pockets, turbulence, and other issues.
November 16, 2007 12:33:34 AM

You shouldn't necessarily try to balance intake and exhaust rates, as this creates stagnant areas instead of a pressure differential causing air to flow in or out certain case areas like vent holes which are in the case for this purpose. Sometimes vent holes are poorly placed but generally it's better to have some than not unless you have a lot of drives in the front HDD rack, in which case you would want as much front bottom intake through the drive rack as reasonably possible, but that only means having a fan not necessarily at a higher rate than the exhaust fan.

Whether intake or exhaust fan rate increase is best depends on your specific case and parts, and whether you are trying to filter the intake. If trying to filter the intake then you do want a higher intake flow rate through the fans so all intake air is filtered. This is significantly louder than having only a non-filtered passive intake.

Do you need an intake fan at all? Unless you have densely stacked or poor HDD rack or poor entire case (especially insufficient size rear exhaust fan) you may not need a front fan at all. If you had some high heat generating parts like SLI'd video cards, try a fan on the side panel directly across from those cards but if you put a fan there be sure to have one in the front still.

Every system is different and with some it won't matter much which way you bias the fans. It would be quicker for you to just try the system one way monitoring temps, then switch the fans and check temps again, than for us to try to list every possible parts, case, and fan combination.
November 16, 2007 1:40:06 AM

Here's something to ponder:

When the fire department wants to remove smoke from a house they open all the windows and blow air into the house at a high pressure and volume.
This creates a great amount of turbulence and removes the smoke from the house very quickly.

My newest build uses the Antec 900 case that has 2 12cm fans in the front, and one 12cm fan on the side pushing air into the case. With 1 12cm fan at the back and 1 20cm fan blowing air out of the case.
Most of the time my Q6600 is in the 42c to 46c temp range using only an Arctic Freezer 7 Pro for a HSF. The ambient air temp is around 72f.
The fan in the PCPower 610 watt silencer PSU only servers to remove the heat generated by the PSU.
The positive air input does seem to work well in my case.

!