do input and output CFM need to be balanced?

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happyguy82

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Aug 25, 2012
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Hello all,

I'm in the process of configuring a new gaming PC. It's my first build in over a decade. I am also new to water cooling.

To get into specifics, I am thinking of using the Corsair 750D. I need to dissipate 600W of thermal energy, therefore require at least 3x120mm (1 x 360mm radiator) to be mounted on the top.

Now here's where I'm confused:

1) Should the fans on the top mounted radiator be pulling in air from the outside or pushing air out? The diagram shows it being an exhaust, i.e. 2 x 140mm high airflow fans at the Front pump air in, 3 x 120mm at the top radiator push air out and lastly 1 x 140mm high airflow fan at the rear to exhaust air out.

2) Here's the real confusion. If the radiator fans are set to push hot air out, wouldn't the casing the left in a low pressure state? This is because I'll have 4 fans pushing air out and only 2 at the front pulling air in.

I guess to simplify the question, do the intake and exhaust fan CFMs need to cancel each other out so the net is zero?

I'm sure this is a very silly question. Thanks in advance anyway.
 
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The only thing that will make a difference is if you push warm out thru the system to cool the CPU or if you pull cool air into the system to cool the CPU. It's a very, very slight trade-off in temps. You can choose between a few degrees, no a fraction of a degree of better CPU worse system/GPU temps or worse CPU and better system/GPU temps. That is the major difference between using a radiator as an exhaust or entry-point for airflow in a system.

Generally positive pressure is better. Dust gets caught in the filters and less is deposited on components inside keeping a cleaner look longer. Honestly, really in all honesty it does not matter. There have been countless videos all over the web over many years of people doing these same...
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offroadguy56

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The only thing that will make a difference is if you push warm out thru the system to cool the CPU or if you pull cool air into the system to cool the CPU. It's a very, very slight trade-off in temps. You can choose between a few degrees, no a fraction of a degree of better CPU worse system/GPU temps or worse CPU and better system/GPU temps. That is the major difference between using a radiator as an exhaust or entry-point for airflow in a system.

Generally positive pressure is better. Dust gets caught in the filters and less is deposited on components inside keeping a cleaner look longer. Honestly, really in all honesty it does not matter. There have been countless videos all over the web over many years of people doing these same exact experiments with mixed results. But ultimately you only get a degree or 2 of difference between 1 fan and 5. Same story with Push/Pull configurations. Pulling air thru the radiator is better than pushing it thru as the dust will collect right on top of the radiator as opposed to between the fan and radiator in a push config, forcing you to un-mount the fans to clean. Having positive pressure or negative pressure doesn't mean a thing except for dust control. Positive is better if you want less dust.

 
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happyguy82

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Thank you guys.

Silly question but how to measure whether the pressure in the case is positive or negative? would a basic barometer like the iPhone 6s be sensitive enough for this?

By the way, the water loop will cool CPU, GPU and Motherboard so all will be affected.

I was worried about 'pushing' air through the radiators due to dust build up between the fans and rad, but if the the radiator is top mounted in an 'exhaust' configuration, how can I use a Pull configuration? Would I mount the fan between the rad and casing?

Thanks again.
 
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happyguy82

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Hi,

Further to my response above, what if I set it up like this:

1) 2 x 140mm high air flow Intake fan at front

2) 3 x 120mm high static pressure Intake fan at top (for 360mm rad)

3) only 1 x 140mm high airflow Exhaust fan at the rear.

With this set up would the pressure in the case become 'too positive'?

Thank you.
 
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happyguy82

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Thanks. Hmm in that case then I should configure No. 2 as exhaust i.e. pushing air out from the top of the casing right?

Thanks.
 
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13thmonkey

13thmonkey

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in at front, bottom and sides, out at back and top with the heat sink pushing front to back.
 
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