[SOLVED] Case Fans & CPU Airflow issue that I think* I'm going to have (CPU fan direction and case exhaust).

Aug 22, 2019
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Up front; first gaming rig that I "built". Buddy gave me his old PC when he upgraded, and I fixed it up for about $300 which was nice. I had to replace an existing fan on the case that was broken, which long story short, led me to realizing and then questioning something about the airflow that might be happening in this case.

I bought a BeQuiet CPU Cooler that many people said would be great for noise, but was fairly large so to make sure it fit. After getting the mobo and such to replace, I ended up only being able to mount the CPU Fan in one direction that it would fit, that being the fan is blowing INTO the case across the fins from the back. The RAM that I already had (Ripjaws V 16G DDR4) was too tall to enable the cooler to be placed any other way. This was all before I did research and realized which way a CPU fan blows, so I assumed it was fine.

View: https://imgur.com/a/IUBZ7wU


Image for reference [mobo and fan are not screwed in since I'm moving stuff around]. I guess my question is, knowing this is how it has to be mounted due to the RAM being in the way, what should I do about the other two fans? The case has two front fans blowing in over the drives, and then it also has a 230mm side intake fan as well for reference. I'm more-so looking for direction on the remaining to (the black 120mm on the back, and the clear 200mm on the top).
  1. The back fan is the one I just replaced. I put it on backwards accidently the first time, and when I went to fix that, is when this all came to my mind. Should I still have the back fan blowing out even though it will be less than an inch from the CPU intake side? Will that be removing unnecessary colder air away from the CPU intake? Making this fan an intake however seems like it'd be bad since then I'd only have the top fan as an exhaust along with any natural airflow.
  2. The top fan is a second question then. Right now it's towards the back and set as an exhaust out the top. Assuming this should be kept as such, but do you think I should move it back to the other mounting area [right in the photo] so that it'll be more directly over where the CPU air is coming out? Or would it be fine where it is towards the back?
Another option that I'm looking into is removing the heat-sink from the RAM sticks which should (hopefully) allow the CPU cooler to be mounted the correct way. Would this just be the better current solution? I'm trying to avoid having the purchase anything else at the moment, but it's something I can/will likely do in the future to fix the issue. Assuming a slightly more slim CPU cooler would be the best idea, but I was still trying to prioritize quietness.
 
There is another easy solution. Reverse the CPU cooler FAN, not the entire cooler.

See those little metal clips on each of the four corners of the fan? They are springs that hold the fan against the heatsink of the cooler. Open those clips, remove the fan and just turn it around, then re-fasten the fan to the SAME (rear) side of the heatsink. This will make the fan into a "pull" configuration, rather than a "push', which will have almost no impact on the amount of air flow you get. But it WILL change the direction of the air flow, so air from in FRONT of the cooler (over the RAM, to the right in your photo) will be drawn through it and then sent directly into the rear exhaust fan. No other changes necessary.
 
There is another easy solution. Reverse the CPU cooler FAN, not the entire cooler.

See those little metal clips on each of the four corners of the fan? They are springs that hold the fan against the heatsink of the cooler. Open those clips, remove the fan and just turn it around, then re-fasten the fan to the SAME (rear) side of the heatsink. This will make the fan into a "pull" configuration, rather than a "push', which will have almost no impact on the amount of air flow you get. But it WILL change the direction of the air flow, so air from in FRONT of the cooler (over the RAM, to the right in your photo) will be drawn through it and then sent directly into the rear exhaust fan. No other changes necessary.
 
Aug 22, 2019
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There is another easy solution. Reverse the CPU cooler FAN, not the entire cooler.

See those little metal clips on each of the four corners of the fan? They are springs that hold the fan against the heatsink of the cooler. Open those clips, remove the fan and just turn it around, then re-fasten the fan to the SAME (rear) side of the heatsink. This will make the fan into a "pull" configuration, rather than a "push', which will have almost no impact on the amount of air flow you get. But it WILL change the direction of the air flow, so air from in FRONT of the cooler (over the RAM, to the right in your photo) will be drawn through it and then sent directly into the rear exhaust fan. No other changes necessary.
That was an initial idea that some research pointed me to, but there seemed to be a LOT of debate on if that was actually good for the cooler or not. Air is supposed to blow across the fins to dissipate the heat, but I guess (and am assuming) the suction by the fan's air flow would do a similar thing?

Just looked up the specs for the fans. The CPU Cooler fan is 400-1400rpm, while the back fan has a Max rating of 1500rpm. That should be fine? If not, I could always just move the back fan up top on the spare mount area just because and simply reverse the CPU fan.
 

Dunlop0078

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That was an initial idea that some research pointed me to, but there seemed to be a LOT of debate on if that was actually good for the cooler or not. Air is supposed to blow across the fins to dissipate the heat, but I guess (and am assuming) the suction by the fan's air flow would do a similar thing?

Just looked up the specs for the fans. The CPU Cooler fan is 400-1400rpm, while the back fan has a Max rating of 1500rpm. That should be fine? If not, I could always just move the back fan up top on the spare mount area just because and simply reverse the CPU fan.
It would certainly be better than having your exhaust fan and cpu fan fight each other. How I understand it you currently have have your rear exhaust blowing out of the case and the cpu fan blowing towards the front, they could cancel each other out set up like that.
 
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DMAN999

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The CPU cooler fan should be a static pressure fan so it should pull the air through the cooler fins just fine.
The rear exhaust fan should also help draw air through the CPU cooler.
I would run it like that and see what CPU temps look like before doing anything else.
 
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Aug 22, 2019
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It would certainly be better than having your exhaust fan and cpu fan fight each other. How I understand it you currently have have your rear exhaust blowing out of the case and the cpu fan blowing towards the front, they could cancel each other out set up like that.
That's kinda what I was assuming would happen. My other option would be to reverse the back fan so that it's also coming in... but that brings many more problems I'm assuming since I'd then only have the top fan as an exhaust.

I mean, as a temporary [month or two] and free solution with what I have now, would it be better to flip the CPU fan, run them normal and see if anything bad happens temp wise, or pull the heat-shields off the RAM which would likely allow me flip the CPU Cooler altogether correctly in everyone's opinion?

My plan a month or two out would like be either buy different, smaller fitting RAM so that I can rotate the CPU Cooler; buy a different, more slim CPU cooler that would fit the correct direction; or possibly buy a new MOBO if I realized that I wanted more/better things on there anyways once I actually start gaming on it.
 

DMAN999

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I would just reverse the CPU cooler fan, leave everything as it is and see what the CPU temperatures are.
As Paperdoc pointed out that will keep the airflow moving the way it should, from the front of the case to the back/top.
I would NOT reverse the rear exhaust fan, that will definitely disrupt the airflow pattern.
 
First, thanks for Best Answer. I agree with others that you should make this fan-flip move only and leave the rest unchanged. I should work just fine.

For most fan designs, whether airflow impedimets are at the fan intake or outlet makes little difference. So turning the fan to place it in a "pull" orientation with respect to the heatsink, rather than "push", should make very little difference to air flow and heat removal by itself. But changing the direction of airflow in that area so nothing is "fighting" with anything else certainly will improve it a lot. The near proximity of the rear exhaust fan that moves the air in the same direction will NOT impede the CPU cooler. In fact, it will aid that. And do not worry about the relative speeds of those two fans. What matters for BOTH of these fans is air FLOW, not fan speed. And the flow generated by the CPU cooler fan on the heatsink is less than the fan alone can deliver under optimal conditions, because the heatsink itself reduces air flow due to the narrow flow space between fins.

The only possible "downside" I can see for this is something you cannot really eliminate because of overall layout. Arranged as I suggest, what I think will happen is that most of the air removed by the rear exhaust fan will have come from case front, up over the RAM, through the CPU heatsink, and out the rear fan. That is, the air flow from the BOTTOM front of the case and over the BOTTOM of the mobo may not be very high since it has no good path up to the rear exhaust fan. From your photo it appears there are four small PCIe slots below the CPU that are empty, so if there really are very few items in that lower part of your case, this may not matter at all. I doubt there is a place on the lower back of your case to mount another exhaust fan. But you MIGHT consider adding a front INTAKE fan near the bottom to increase air flow over that area of the mobo.
 
Aug 22, 2019
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First, thanks for Best Answer. I agree with others that you should make this fan-flip move only and leave the rest unchanged. I should work just fine.

For most fan designs, whether airflow impedimets are at the fan intake or outlet makes little difference. So turning the fan to place it in a "pull" orientation with respect to the heatsink, rather than "push", should make very little difference to air flow and heat removal by itself. But changing the direction of airflow in that area so nothing is "fighting" with anything else certainly will improve it a lot. The near proximity of the rear exhaust fan that moves the air in the same direction will NOT impede the CPU cooler. In fact, it will aid that. And do not worry about the relative speeds of those two fans. What matters for BOTH of these fans is air FLOW, not fan speed. And the flow generated by the CPU cooler fan on the heatsink is less than the fan alone can deliver under optimal conditions, because the heatsink itself reduces air flow due to the narrow flow space between fins.

The only possible "downside" I can see for this is something you cannot really eliminate because of overall layout. Arranged as I suggest, what I think will happen is that most of the air removed by the rear exhaust fan will have come from case front, up over the RAM, through the CPU heatsink, and out the rear fan. That is, the air flow from the BOTTOM front of the case and over the BOTTOM of the mobo may not be very high since it has no good path up to the rear exhaust fan. From your photo it appears there are four small PCIe slots below the CPU that are empty, so if there really are very few items in that lower part of your case, this may not matter at all. I doubt there is a place on the lower back of your case to mount another exhaust fan. But you MIGHT consider adding a front INTAKE fan near the bottom to increase air flow over that area of the mobo.
That photo was with things taken out and unscrewed since it was too tight to work with that large CPU cooler. Once set up, I will have a GTX 960 in that top PCIe16 slot. I will have a capture device in the lowest PCIe1 slot as well, but that generates very little heat compared. There are already two intake fans on the front drawing in air over the HDD slots. One is placed directly over where I installed a 1TB HDD (which will only be secondary storage as I have a M.2 on the MOBO)... but the other is directly on the bottom and basically unimpeded by anything.

View: https://imgur.com/a/XjprHXP


That's an updated picture with more of "everything" in it. Fan has been reversed already. You can see where the two fans on the front are located, and where the one HHD is poking out. The graphics card is in, and just the small PCIe other card is missing since that's still in my home PC atm.
 
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Yes, I can see now that the air flow should be good. The majority will enter near the bottom front providing lots to the graphics card. Then most will have to swirl back around that card to get to the upper section where the RAM, CPU etc. are cooled before the exhaust fans remove it.
 

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