Colin's Weekly Tip: Negative Pressure is good!

[Colin]

One thing I've noticed when talking to novice computer enthusiasts are that they often use too many case fans in an attempt to keep case temperatures down. While their hearts are in the right place, most run into the common problem of having too much 'positive air pressure.' <BR><BR>What I mean is, if there are more fans blowing air into a case than exhausting from it the air pressure just builds up. What we need is the airflow entering into the case to be matched by the air exhausting from the case so air currents don't stall.<BR><BR>If the air has no where to exit, it can't very well cool your $500 videocard any better now can it? What I recommend is that enthusiasts focus on creating a situation where your case has negative air pressure (more exhaust fans than intake fans simply) inside a case.<BR><BR>This has the tendency to pull fresh cool air into the case, and ensure some guaranteed air flow in and around the exhaust fans. In most cases, a system with negative air pressure should run cooler than one with positive.<BR>

[jakester]

I advocate supplying more air into the case than is being exhausted for one specific reason - to keep the case and components clean. This assumes of course that you use filters on all fans that blow air into the case (as I do). Bear in mind, the case is far from airtight. Neither of our methods will cause significant positive or negative pressure in a case. All it does is determine whether the net airflow is either into or out of the case. Ensuring that the net airflow is out of the case, means that all of the air going into the case has been filtered. The excess air - which has been filtered - finds its way out through all the various small openings, like ventilation holes, gaps around the card slot covers, bay blankoffs, etc. Air can also find its way out through the externally open bays like floppy drives, zip drives and optical drives – they aren’t airtight either. If more air is exhausted than supplied, air finds it way into the case through all those various pathways, bringing with it dust and dirt. The case and components stay much cleaner if the amount of filtered supply air exceeds the amount of exhaust air. Naturally, you just have to vacuum the filter media on a regular basis. Every 2 or 3 weeks works for me. You may be surprised as to how much dirt builds up. Better in the vacuum bag than in the PC case!

[NotMyBest2Day]

i advocate negative pressure. i've noticed significantly lower temps with negative pressure than postive. i have 7 total 80mm fans on my rig, and my original configuration was 2 intake, 5 exaust. i know i had very good negative pressure, because when i open up the side of the case, all the fan speeds drop 8% (thanks to MBM5's dashboard), even the CPU fan drops a little, too. i was getting a little on the warm side, oddly, today, so i took the side panel off and reversed one of my exaust fans (since it is very close to being over the CPU). now i'm at 3 in, 4 out, and that did help a little more with temps.

i agree that there are lots of holes and such in a case, and that it isn't airtight, but positive and negative pressures still do have a considerably noticeable difference in flow and temps.

negative pressure is good.

[LBJGH]

I like the balanced approach... 120mm intake and exhaust... + PSU. I figure the case leaks just enough to balance the PSU fans. :)

[ted]

the psu exhausts air from your case so if you have 2 of the same fans 1 in and 1 out really there is have negative pressure. personally i think this is the best setup.