# Positive or Negative Case Pressure?

Hey everyone.

Getting my computer together has raised a few questions about case airflow.

Should I have positive or negative case pressure?

I would like to eliminate as much dust as possible, but also decrease case temps.

Am I able to have both, or just one?

You should have slight positive air pressure, to avoid dust buildup. The way to implement it is factor of the setup you have. I use "wind tunnel" cases (the entire front is made up of fans without anything else, and I can see right through the case, there is a wind tunnel above the GPUs and the CPUs, and because of the fact that a lot of air is moved through them every minute, the speed of the air stream inside the case is high, which makes the pressure lower, so I need more rpm on my intake fans than on my exhaust fans. If the airstream is hindered by obstacles or sound insulation or whatever may hinder airflow, there will be spots, or even whole areas of the case where the airstream velocity is nearly zero. That will increase the pressure enormously, you in those cases, exhaust fans are more important.

Just apply Bernoulli's law, and you'll be just fine. Do not believe Linus Tech Tips are other marketeers, calculate your result. You can perfectly calculate the useful surface of your fans: pi.(diametre/2)²-pi.(hubdiameter/2)². That can be used as a measure of airflow potential. If you use all the same type of fans, you can then use the rpm of the fans to perfectly finetune your airflow, depending on the kind of case you have. Check the slight overpressure inside the case in a spot where you can feel the draft of the airflow with any barometric device at your disposal (2 minute DIY if you don't have a barometer/altimeter: seal a glass test tube or narrow shot-glass filled with a little water and a lot of air tightly with a cellophane, hang it straight upside down with some heavy duty double sided tape inside your case in a safe spot, and take a picture of the water level. Then do the same outside of the case (which is where you sealed the thing, which means the pressure inside the tube should be the same as the atmospheric pressure outside the tube, but maybe you filled it up in the kitchen downstairs and you're now measuring upstairs in your room, which makes a difference in barometric pressure). Magnify the pictures, and compare the water level. If the water level is higher inside the case, that means the cellophane was compressed, so the atmospheric pressure inside the case was higher than outside the case, which is what you want.)

Zoltan, sir, hats off to you.

All I can add is what George Makris from Corsair (the guy who created the 800D and 900D) said when asked the same question. He said that they did tests in the lab and they got the best results when the amount of air entering the case was equal to the amount of air exiting the case. My advice is exactly Zoltan's advice: make sure the air pressure inside the case is slightly higher to minimize dust build-up, while still having good cooling.

my previous case worked with positive air pressure, not much dust, but also resulted in higher temperatures, that's why i bought my recent case (fyi: antec 900)

He said that they did tests in the lab and they got the best results when the amount of air entering the case was equal to the amount of air exiting the case.

Rien ne se perd, rien ne se crée... (Lavoisier)

I use positive air pressure with dust filters on all the intakes and almost never clean dust out of my case.

Yup, I've been using these for a long time now, I guess almost 10 years or so, they still pretty much look like new. I always mount the third framed fan (drive cage fan) in the front on top, so that the entire front is covered by the three 120mm Antec TriCools. I have a lot of drives in my cases, 7 to 9 of them, so the Antec 900 is ideal, because I still have space for more, and still the case achieves almost laminar flow, there are almost no dead spots inside. Best cooling case ever. Not such a good case for cable management, but not too big either, more practical format that recent cases, that don't have such a good airflow, such a solid chassis, such long-life materials or so many easy to use drive space. But unbeatable case for the price, and my temperatures speak for themselves, I barely go over 35 °C with maximum overclock (and that's really pushing it hard, typically more than 25% overclock with liquid cooling with high alcohol solutions in a loop that allows the alcohol to just start to boil without creating overpressure). I wish I could cool with mercury, that would be really efficient, unfortunately it's quite illegal because of the toxicity, but it would definitely be the most advantageous cooling solution for heavily overclocked CPUs, and it would also look great and stay really clean for decades, without any erosion or oxidisation. If mercury cooling were legal, I'd be the first to use it, imagine the huge overclocks that would be possible...