Forward top case fan mounting efficiency


Oct 23, 2014
Hi, I am having some trouble understanding optimal case fan setup for an air cooled system. I have been reading around but different accounts conflict with one another. Specifically, some accounts say that using a top forward case fan reduces temps while others say that it increases temps.

Mounting points for for my H400 case are:

2x 120mm/140mm front
2x 120mm/140mm top
1x 120mm rear

I understand that front/bottom are generally best for intake and top/rear are generally best for exhaust. However, the case is fairly small and has no drive cage so it seems that some intake air will be exhausted by the forward top case fan before it has a chance to cool anything. This mount point seems more for an AIO/radiator setup.

My cpu will be air cooled and I don’t want to use a setup that directs intake air away from components. Right now, I have 2x 140mm intake and 3x 120mm exhaust but I am waiting on a few more components before I can start the build. I was considering changing the top exhausts to 140mm to help with noise.

Anyone happen to know if that forward top fan is a hindrance? If so, any ideas on how to balance my airflow without just reducing rpm on the intakes?

Many thanks for any help!


Dec 22, 2016
I haven't ever mounted top fans, so I can't speak to that.

But I can say this, from recent experience: I just built a new system with a Ryzen 7 2700X and Radeon RX 580. I have 3 front intake fans and 1 rear exhaust. (My PSU has a separate chamber, so its exhaust doesn't count.) My CPU is able to turbo to its maximum turbo frequency without going above 75 C (85 C is the maximum safe temperature). My Radeon never goes above about 60% fan RPM at maximum load. And my 9 different system sensors (chipset, VRM, RAM, etc.) never go above about 40 or 50C.

Originally, I had 2 intake fans and 1 exhaust, but I added the 3rd intake fan because my system was silent, so I had nothing to lose by adding it. (My fans are all silent models, and my case has noise insulation.) But my temperatures didn't decrease.

So my point is, I think that 2 intake fans and 1 exhaust are probably enough, unless you're doing some serious overclocking.

Anyway, while I've never mounted top fans, my understanding is what you've heard - that you're better off with front intake and rear exhaust. I would be afraid - as you are - that top-mounted exhaust would just exhaust the cool intake before it has a chance to cool anything. I would also be afraid that top-mounted intake would just add turbulence without contributing much extra cooling.



May 23, 2018
I agree that the two intake in front/one intake in rear is the traditional setup and works in most cases. BUT every case and setup is a bit different, so I would really encourage you to try a couple different setups and see for yourself. Especially experiment with those top fans...test with no fans, then intake, then exhaust. That way you KNOW what's best for YOUR machine instead of listening to all of us old geezers.


Oct 23, 2014
Thank you both for the advice. I just got back from grabbing some 140mm fans for the top so when I put everything together I can test pretty much every scenario. They are rgb so I doubt I would switch to intake for aesthetic reasons, but I’ll at least test it for curiosity’s sake.


Apr 3, 2018
Now that a few people have made comments, I will add my thoughts.

I was having some cooling issues in my case. I added a couple of fans that were supposed to be intake, but the design of them and the case would not allow them to be mounted that way without the blades hitting the case itself. They only worked as exhaust fans. In general I have noted the computer idling about 2-3C cooler than it did before. On the high end I really can't comment that it changed anything much, but the additional heat coming off the graphics card being sucked across the mobo probably isn't helping there...before I would just reach a saturation point where the whole case was hot.
I still have not purchased "caged" fans to add to the front plane.