Excuse me....

I was wondering about positive/negative pressure. I understand that positive has more air going in than out, and negative the opposite. why would you get more dust if you have more air going out? I would think its the other way around. Could someone clarify this for me. Thanx

If you are moveing more air out, through fan openings, than in the theory is that you are pulling air and dust in through the seams. The fact is there is no real pressure unless you seal all the seams which is almost impossible. I for one don't buy into this theory.

id have thought that if u had more goin in, then u wud have higher air pressure in the case, which wud hold more heat, and force any dust to enter the case to settle easier

The pressure created by case fans is so low, it would not create an ability to hold more heat, at least not anything noticable.

Talon101 said:

I was wondering about positive/negative pressure. I understand that positive has more air going in than out, and negative the opposite. why would you get more dust if you have more air going out? I would think its the other way around. Could someone clarify this for me. Thanx

Click to expand...

The theory is that of a vacumn cleaner.. if you have negative pressure inside the case dust would be sucked in and attracted towards the case. The biggest defence for positive pressure is not the 'dust' theory but the fact that it keeps the air moving and reduces the opportunity for hot spots to form in the case.

Right, it kinda assumes you have filters over your fans (so not much dust enters that way). Then, negative pressure will suck air in through the holes in the case (so the theory goes). If you dont have decent fan filters then the whole theory is shot, since youre gonna have a bunch of dust in the case regardless of pressure. As to pressure and heat, I think it depends on the individual case setup...seems to be different for different people, so its probably something youd have to try and see.

The theory of positive pressure and dust control must hold true. All Fabs (chip factories) maintain a positive pressure and is constantly monitored to be sure it is maintained. I am currently designing a test wafer disposal chute for fab 20 (intel) and one of the design criteria is that it maintains the positive pressure at all time. We must maintain class 1 cleanroom environment. This means 1 .5 micron particle per cubic foot of air. to put this in prospective you can put 50 such particles on the end of a hair. Of course we use filters but air flow plays a big part in the system. Just an interesting FYI

Positive pressure DOES work, and it is a real thing- just that our use of the term is...well wrong

The fans used in computer cases aren't really strong enough to maintain a pressure differential; instead we use it to describe how we plan the airflow to move:
"positive" means that we are trying to force more air into the case than out- which sends some air out of the case through all the cracks and seams.
"negative" means that we are trying to get more air out than in- trying to get air INTO the case through all those little seams.

I have (almost) always found that slightly negative works better at reducing hot spots and dead air space in my cases.

A highly subjective topic though- my best suggestion is to always EXPERIMENT! Find out what works best for YOU.

I'd definitly err on the side of more air flowing in. My Lian-Li had more going out until reciently, and I kept having dust being drawn in around the PCI cards. ; D Also, less air tends to create miniture vacuums where heat can arise.

Wow! thanks for all the info, I'll experiment with the fans, right now i have 2 fans blowing air in and 1 out (psu). My bios is crap so it doesn't tell me the temps of anything, so i basically have to guess.. but anyways, thanks again for the responses

When it comes down to it, it completely depends on what case you have and how the fans are positioned. If you can visualize where the air is moving, as well as where it isn't, you can plan & adjust accordingly.

Positive air flow might work well in one case design, while negative will work better in another.