Positive case air pressure

Mark_D · 20 Jul 2016 at 15:27

About to start my new build. Is maintaining positive air pressure inside the case simply done by having more intake fans than exhaust ones? Or am I going about it all wrong?

Smffy · 20 Jul 2016 at 15:37

Pretty much yeah, just think of it like you need the air to want to leave at the back... Pushing more in the front has that effect, using the top to vent is also a good shout given hot air rises naturally.

puppetworx · 20 Jul 2016 at 16:17

You can also run an equal number of intake and outtake fans and use software to lag the speed of the exhaust fans behind the intake fans.

doyll · 21 Jul 2016 at 10:55

Mark_D said:
About to start my new build. Is maintaining positive air pressure inside the case simply done by having more intake fans than exhaust ones? Or am I going about it all wrong?

We really need more information to help you setup your case airflow. What case, motherboard, cooler, GPU, fans used where it will be placed, etc.

While technically it positive pressure, it is really pressure differential .. and that difference is almost no pressure at all. If you stand on a slope the pressure where you are standing and the pressure up the slope about 10 feet higher there is more pressure difference than between inside and outside of case.

So while most think of it as 'positive pressure', It is really about a case only flows as much air as the smaller of the two; intake or exhaust.

For intake to put air into case an equal amount of air must leave the case.
For exhaust to take air out of case an equal amount of air must enter case.

Having slightly more intake flow potential means air leaks out un-fanned vernts and other openings, not in.

That is the simple part. Case vents, especially front ones are usually quite restrictive (30-60% restriction) made even worse by filters that restrict even more of the airflow, especially at lower rpm.

Rear case vents are about half as restrictive as front.

When air cooling the top vents (all but very back one) are usually counterproductive. Back one is only maginal at helping because there is usually a back exhaust near top of case back.

While hot air does rise (because it expands when heated making it lighter than cooler air), to do so requires no fans creating air movement. A fan even at very low speed immediately overpowers the 'warm air rising' concept

What we want is front to back airflow. This moves the heated air from GPU back and not up into the area of CPU cooler.

About half of my cases don't even have exhaust fans .. only filtered intakes. The principle is the same as on a cooler or radiator. With the right fans we don't need push/pull much of the time.