[SnowStorm86]

I am thinking about building a desktop rig as a project for 2013.

I'll probably have a bunch of questions over the next few months but my first is relating to ventilation, and specifically air in/air out ratios. Should the case be taking in more air than it exhausts? Or should it exhaust more air than it takes in? Or should it be 50/50?

Having googled this already, there does not seem to be a strong concensus on this issue with different people favouring different setups.

[anniebrion]

My PC has far more fans sucking air out than in.

I have 1 fan at the base sucking in and 1 at the rear top and 2 on the top sucking air out also the graphics card suck air out.

[flagpole]

the pc will necessarily suck as much air in as it blows out.

what you do will depend on your situation. in particular how it's vented. if you have two 40 cubic feet per minute fans sucking in you will have air flow of 80cfm. if you have one going in and one going out you will have a total airflow of 40cfm. if you follow.

that having been said dust is an issue. if you intend to put dust filters on the input fans then it's useful to have the system at over pressure because if it's at negative pressure dusty air will be drawn in through the gaps.

[SnowStorm86]

The case I'm going to be using (Corsair 650D) I believe comes with a pre-installed dust filter for the front air intake. Flagpole you've lost me a little when you mention "negative pressure" and "over prsesure". What configuration would successfully achieve over pressure?

[chrisjr]

Originally Posted by SnowStorm86

The case I'm going to be using (Corsair 650D) I believe comes with a pre-installed dust filter for the front air intake. Flagpole you've lost me a little when you mention "negative pressure" and "over prsesure". What configuration would successfully achieve over pressure?

It simply means the air pressure inside the case relative to the outside.

If the inside pressure is lower then that is negative and if higher it is positive or over.

Negative pressure means air will naturally flow into the case through any gaps. Positive pressure means it will naturally flow out of the case. The latter is desirable as it means dust is not being sucked into the case through unfiltered gaps in the case.

To achieve positive pressure you suck more air into the case than you suck out, in very crude terms.

[flagpole]

Originally Posted by SnowStorm86

The case I'm going to be using (Corsair 650D) I believe comes with a pre-installed dust filter for the front air intake. Flagpole you've lost me a little when you mention "negative pressure" and "over prsesure". What configuration would successfully achieve over pressure?

if you have more fans sucking in than blowing out there will be a slight excess of air in the case which will force air out through any gaps that might exist. and they always to exist. either as actual air vents, or just gaps in your card reader, around the optical drive or whatever. if the opposite is true, if you have more fans taking air out of the case then air will be drawn in through these gaps.

of your case has filters then you really only want air going in that has been through the filter.

i wouldn't stress about this to be honest.

[SnowStorm86]

Thanks. I've also read that air intake should be low on the case and air exhaust should be high. The theory based on hot air rising. Anyway thanks, I've got a better idea of how to take this forward now.