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My PC has only the basic 2 front intake fans and 1 rear exhaust fan. There are space for 2 more at the top and I'm considering whether it's worth installing more fans when I upgrade to some hotter components, but my research is giving me conflicting information.

To be clear, I'm not asking "whether I really need more cooling", as I believe that is too opinion-based and subjective. Rather I'm asking whether there is a way of configuring more fans that would provide more cooling (regardless of whether I "need" more cooling). And especially I'm after objective explanations of how the conflicting principles I've found in my research should be assessed against each other, in the hope that I will learn how to assess similar decisions in future; I don't just want opinions about what the "best" principle to follow is without some explanation of why that one trumps all of the other concerns.

Here's what I've got currently:

Current PC setup

(The case is a Corsair Carbide 540 Air, so the PSU and drives are in a separate compartment at the back of this picture, out of the main air flow)

Here are my concerns:

  1. The general advice seems to be that top fans should be exhausts, on the principle that heat rises. However adding 2 exhausts would create negative pressure, which I would like to avoid.

  2. Currently there is the nice clear air flow from the front intake through the CPU heatsink fan and out the exhaust (there's obviously hot air coming up from the GPU as well that has to merge with this, so the picture is more complicated than my nice arrow). Some of my research has suggested the option of turning the rear fan around to be an intake and then adding exhaust fans to the top, but this seems like it could risk turbulence from the rear intake fan blowing directly against the CPU heatsink fan. In fact, would adding any airflow from the top fans risk be counterproductive by disrupting that clear front-to-back flow?

  3. That same current flow almost suggests that if I was going to mount fans, an exhaust at the top-front would be counterproductive (it would mostly remove cool air that's just come in from the front-top fan), and an intake at the top-rear would be counterproductive (it would just add cool air to the region where I'm channelling all the hot air for exhaust out the rear fan. This almost suggests I could do one intake and one exhaust on top, but I gather that risks just creating a circular flow between the two adjacent fans blowing in opposite directions (pulling hot air from the exhaust back into the case).

So then the options I'm considering (in no particular order) are:

  1. Add one intake at the top-front, and one exhaust at the top-rear.
  2. Just add an intake at the top-front.
  3. Just add an exhaust at the top-rear.
  4. Turn the rear fan around so it's an intake, and add 2 exhaust fans to the top.
  5. Do nothing, if the top fans would only be counterproductive or marginal for the overall cooling of this system.

But I don't know how the various concerns should be weighted against one another to come up with a decision. If it's possible to reason out which option is likely to be work the best, then I'd like to know both (a) what it is (or some none-of-the-above option) and (b) what the reasoning is that leads to that conclusion.

Obviously once I've bought the fans I can monitor temperatures and do some experiments, but if general principles strongly suggest one particular option (especially the do-nothing one) then I'd rather start from there.

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    1. If your PC is not overheating, why do you need another fan? 2. Consider that more airflow also pulls more dust through the PC. May 5, 2019 at 3:58
  • @DrMoishePippik That's a very valid thing I need to consider, but not actually my question here. I deliberately didn't give any of the information you need to answer whether or not I need another fan, because this isn't a discussion forum and I don't want to get sidetracked on this question; even if I don't end up adding more fans, the answers I'm hoping for will help me understand how to make similar choices in future.
    – Ben
    May 5, 2019 at 4:33
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    I was quite disappointed when this question was closed as opinion-based, given my whole purpose for asking was to try to get some objective information because the internet abounds with conflicting opinions on what principles you should use to configure your cooling system. But at the time I accepted it and moved on. However I just received a Famous Question badge for this question, so clearly people a lot of people have been interested in it despite it being closed 2 days after asking. I'm still interested in more thorough answers, 5 years on. Can we consider re-opening it?
    – Ben
    Feb 20 at 1:57
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    @Ben I voted to reopen as expressed in this meta comment. If it’s reopened, I will post an answer. Feb 27 at 1:47
  • There's two reasons to exhaust at the top: 1. getting the help of natural convection to drive flow ... this is bogus as the fans generate pressures that are many orders of magnitude higher than the pressure differentials generated in air over a couple feet with a maybe 10% temperature difference. 2. to prevent hot spots where air doesn't circulate but heat gets pumped... this might be a concern for some cases but it looks like yours has a grill on top and no places where hot spots could hide from the general airflow.
    – Rick
    Mar 1 at 22:24

1 Answer 1

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Update 2024:

Since much has changed in case design and PC components since I initially wrote this answer, I feel it would be a good idea to keep it updated with new information as time goes on. Even though this question is specific to one case design in particular, I'll try to answer with general guidance.

Components such as the GPU and CPU have become much more power hungry in recent years, and as such produce much more heat.

When selecting a new case:

  • Select a case with mesh dust filters at air intakes
    • Ideally these filters should be easily accessible for regular cleaning
  • Select a case with a high airflow design
    • The goal is for air to move freely through the case, to ensure that hot air generated by components is exhausted as quickly as possible, and replaced with fresh air

When building:

  • Prioritize intakes as opposed to exhausts
    • You want avoid negative pressure on the inside of your case, since it's probably not air-tight, meaning that dust will be drawn in through cracks or seams where mesh filters are not present. Having positive or neutral internal pressure will mitigate this.
  • Avoid dead-zones around heat-generating components
    • It's important that the CPU and GPU coolers, some SSDs (including many M.2 drives, with or without heatsinks) and most HDDs have airflow passing over them continuously
    • Most active components will throttle themselves if they get too hot, but in rare cases excessive heat can cause permanent damage

There are many other considerations with regards to cooling to take into account when building a PC, but hopefully these tips were helpful.

Original:

As per Linus Tech Tips:

The case fans make a negligible difference in cooling to those components which have dedicated cooling fan (CPU), but the configuration you choose for your case fans will affect the amount of dust that builds up in your case.

You are better off having a neutral pressure fan setup which outputs to the ground and draws in from the top.

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  • "outputs to the ground and draws in from the top." Depends on your PC case design really. Ultimately, having (removable/cleanable) dust filters would stop the majority of dust from entering and - assuming intakes along the top, would mean the falling dust would land on top of the filters. Better to do intake from the sides and out the bottom, imo
    – Robotnik
    Feb 26 at 4:44
  • @Robotnik When I wrote this, cases with mesh filters at intakes weren't as popular as they are now. Certainly it would be a good idea in today's market to get a case with mesh filtering.
    – Ulincsys
    Feb 28 at 20:40

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