Question Equal amount of intake and exhaust, but does size matter?

libykim

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Jun 2, 2015
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I have two exhaust (rear and top) and two front intakes attached to the radiator of my AIO.

And the sizes are:
2 x 120mm intake fans
and
2 x 120mm exhaust (rear and top)

My question is, the top exhaust also supports a 140mm fan.
Would it be better, worse, or the same to change my 120mm fan to a 140mm?
I heard positive or neutral airflow is preferred, and I'm not sure if a bigger disrupts that.

I'm also guessing that the airflow is already negative in my case as my chassis is a H510 and the intake fans in the front has to pull air through both the narrow filters in the front AND the AIO radiator.
So, what do you suggest guys?
 

Barty1884

Titan
Moderator
It's not strictly fan "size" that will dictate whether you have positive/negative/neutral airflow.....As you alluded to, it's the air movement.

There's arguments for positive, negative & neutral airflow.

If you had four identical fans, but the two intake are pulling through a double layer of filters, or a glass front panel, or Rad etc..... then it's no longer "neutral".


Positive would be my preferred as, at a high level, you'll see less dust.
In an H510 though, you're in a tough position. You're never going to be able to pull more, unrestricted air "in" vs what you could push out.

Switching a 120mm to 140mm as an exhaust at the top, all else being equal (quality, RPM etc), would increase the negative airflow (more air out).

However, another way to look at it - is a 140mm could spin at lower RPM and achieve the same air movement as a 120mm at a higher RPM.
 

Math Geek

Champion
Ambassador
However, another way to look at it - is a 140mm could spin at lower RPM and achieve the same air movement as a 120mm at a higher RPM.
and that lower rpm also usually equates to less noise :) so a second bonus for the larger fans.

you can always fiddle with the fan speeds to try and equalize the air flow or even get that positive number your looking for but that's only if you feel like the effort is worth it. also don't forget that for most people the psu fan is also exhaust. so you likely have more going out that you expect.
 

libykim

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Jun 2, 2015
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Thank you so much for the helpful replies guys!

Another reason why I wanted to replace the top 120mm to a 140mm was because I wanted to completely cover the top grill. It supporting both 120mm and 140mm fans made it have empty grills going around the 120mm fan. I sort of assumed that during operation that would bring in more dust.

Anyway, thanks again. I guess i will b getting that 140mm for more silence AND rgb lighting while I am at it!
 

Barty1884

Titan
Moderator
When you're using the system and the 120mm is pushing air out (as you stated it's used as an exhaust), the 'gap' around the edges will not see any noticeable dust coming in.... air/dust just doesn't work like that.
The fan is pushing a volume of air out... unless you had something pushing dust/air towards the opening, no dust is getting in while the system is operations.

When the system is off... sure, dust could fall in, but that's true whether the 120mm fully covers the opening, or a fan is simply not spinning (which would be the case when the system is off).
 

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