Do I need an extra intake or exhaust fan to create positive air pressure for my system?

[sapped]

Hey guys,

I’m thinking of adding more fans to my system, to cool my GPU and more importantly in controlling the amount of dust getting in to my pc case. Thus I’m hoping to set up a positive air pressure with more intake airflow than exhaust.

However I am confused with the following, because I’m using the massive Noctua NH-D15 CPU Cooler to cool my processor, it has two 140mm fans attached on top of the heatsink like this:

NH-D15

So I have a total of 4 fans (140mm) in my system, 1 intake in the front, 1 exhaust in the back, and 2 fans in between attached to my heatsink. What I’m wondering is, because I’m hoping to create the positive air pressure, does the 2 fans attached to my heatsink count as intake or exhaust?

I can’t find any definite info on this, I remember reading an article stating the CPU fans also affects the air pressure. So I’m hoping to ask you guys, do I need an extra intake or exhaust fan in my situation, to create this positive air pressure I’m hoping to achieve?

Thank you so much for reading and I appreciate your responses!

[profJim]

If both of your Noctua cpu fans are pushing or pulling air towards the rear output fan on the back of the case, my best guess is that there is little (about 25% of one fan's CFM) additional exhaust effect. Keep in mind that both of your cpu cooling fans are trying to push or pull air through the cooling fins.

Intake fan filters reduce the intake airflow quite a bit, but you need to install intake fan filters to minimize accumulating dust buildup inside your computer case.

Don't install a high CFM fan on your side case to help cool your video card(s). I installed an 80 CFM intake fan on my side case to help cool my SLI video cards. This caused too much turbulence and my GPU temperatures went through the roof. A 900 rpm, 140mm cooling fan worked fine with my setup.

My power supply is installed so that intake air is pulled in through the bottom of the case and it immediately exhausts the psu's heated air out the back of the computer case. I don't include the psu's airflow when factoring the amount of airflow into or out of the case.

Holding a piece of tissue paper just above the ventilation holes outside the back of the case will give you an idea how weak or strong your positive case pressure is.

A setup similar to the attached picture might work well for you.

[sapped]

Ahh thank you so much for your detailed reply profJim, sincerely appreciate this!

Just a question regarding your system, do you put your rig on the floor or the table?

And will the bottom intake fan suck in a lot of dust compared to other positions? Even with the fan filter on the bottom. As I heard the bottom intake fan can suck in more dust than usual.

[profJim]

You're welcome.

Because hot or warm air rises I prefer putting the computer case on the floor where the air is a bit cooler. I would have to run a test to see fan filters would clog up quicker when the system is on the floor. Common sense tells me that the only fan filters that might be affected when using floor placement would be the psu fan and any other intake fans that were mounted on the bottom of the computer case. Unfortunately theory and reality don't always agree and sometimes you have to ignore what common sense "told" you was best. Make sure that any carpet or rugs won't restrict air intake.

My computer case is on the floor which has thin compact carpet. The case is setting on two 2 x 4's that are cut to the same length as my case. This way there is an air intake opening underneath both ends of my case and the dimensions of each opening is about 1.75 inches high by about 5 inches wide. Common sense tells me that this setup makes if much harder for lots of dust to find a way into my system.

[profJim]

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Parsec said "Filters restrict air flow a lot, at least 50%."
This sounds high but it might be true.

The attached picture isn't quite what I have in mind, but it shows the fan's airflow.




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