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clevenwj
10-21-2006, 05:50 PM
Do I want to push more air into the pc or more air out? This is my setup with fan position and orientation:

Front lower: 80mm intake fan 25-30 CFM

Back middle: 90mm exhaust fan 30-40 CFM

Top middle: 80mm intake fan 25-30 CFM (Should I make this an exhaust fan?)

Other cooling: CPU heat sink fan, HDD heat sink fan.

I was going to replace my Front fan with a 50-80 CFM fan and make the top fan an exhaust fan.

Here is my temp’s Idle/load
CPU 80F / 95F
HDD 68F / 70F
System 70 / 80F (Ambient air temperature inside the case)

Do I want positive or negative pressure? I have read mixed reviews on that.

I’m trying to get the coolest temperatures from air / fan cooling. Any advice would be greatly appreciated.

Blues
10-21-2006, 09:03 PM
Idle setup is as much air in as out so it circulates but generally PCs are setup to pull out more air then they pull in. You average case, old style not the more recent which are better, had a single fan in the front and a single in the back how ever most power supplys pulled air through themselves giving you sort of in a sense 2 fans in the back. You want to keep fresh air flowing in and keep the temp low so it is more important to pull out the hot air then it is to push in cool air.

Stealth
10-22-2006, 12:40 AM
Do I want to push more air into the pc or more air out?

<snip>

Do I want positive or negative pressure? I have read mixed reviews on that.

I’m trying to get the coolest temperatures from air / fan cooling. Any advice would be greatly appreciated.

As I explained in The physics of good airflow (http://www.technibble.com/case-cooling-the-physics-of-good-airflow/), I believe you're better off trying to achieve positive pressure than negative. The reasons for this are multiple.

First, by having positive pressure, you're ensuring that air only comes in through the fans, not through the cracks between the chassis and the optical drives, as opposed to a negative-pressure case.
Second, by placing intake filters you can significantly lower the amount of dust that comes into the case, and the exhaust wouldn't run as high a risk of clogging as with negative pressure, where unfiltered air can come in through virtually any hole on the chassis.
Finally, if you're constantly pumping in ambient air (which, in most cases, is below 25°C / 77°F), you won't be moving around the same old batch of air that's already inside. Air in a closed system loses "elasticity" towards changing temperatures, but air coming from the outside can take more heat onto itself and get shoved out of the exhaust fans.

Hope this helps.