Anyone ever used 2x exhaust fans at the top?

TheRandomGuy7

TheRandomGuy7

TheRandomGuy7

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After trying this setup in a smaller and compact ATX case, to my surprise it actually lowered GPU temps by a nice amount just from all the extra heat getting expelled out the top of the case.

Does anyone else actually use this or am I alone?

I'm curious whether running the fans at different speeds would be better for airflow (the fan nearest the front intakes running at a slower RPM to avoid messing with the intake too much). And also maybe playing with the speed of only the uppermost front intake fan.
 
Armageus said:
It may work in certain cases, but in general it's better to not fit the frontmost top exhaust, and instead remove any pci-e slot covers and allow the heat to exhaust there
Click to expand...

With 3x front intakes and 1x extra intake on the bottom, it doesn't seem like a bad idea - I'm guessing this shifts the airflow to more bottom --> top as opposed to the more traditional front --> back
 
I'm running 3x120 in push-pull top exhausts.
The important part is getting airflow through the rads and cooling those, so any airflow inside the case along the way cools non-WC components.
 
ttaskmaster said:
I'm running 3x120 in push-pull top exhausts.
The important part is getting airflow through the rads and cooling those, so any airflow inside the case along the way cools non-WC components.
Click to expand...

100% air setup here. I know with many watercooling setups the top is useful for radiators but the case airflow will be much different to a regular air build.

dave28 said:
One 200mm fan on top, another big fan in the front and a small fan in the back
Click to expand...

Do you run the top fan slower than the front intake? If not that's definitely a negative pressure setup so interesting to hear how well it works for thermals (aside from heating the room lol)
 
TheRandomGuy7 said:
100% air setup here. I know with many watercooling setups the top is useful for radiators but the case airflow will be much different to a regular air build.
Click to expand...
I've always run the tops as exhausts, even back when I was on air.
My cases have always had 5.25" bays, though, so there is no conflict with the front intakes. On one of them I also added side panel fans, but that didn't work so well.
 
TheRandomGuy7 said:
100% air setup here. I know with many watercooling setups the top is useful for radiators but the case airflow will be much different to a regular air build.



Do you run the top fan slower than the front intake? If not that's definitely a negative pressure setup so interesting to hear how well it works for thermals (aside from heating the room lol)
Click to expand...

same speed i think, i never thought about pressure to be honest. i think i just set the speed so they are not making too much noise going full blast.

my cpu has a huge aftermarket heatsink that also has a fan on it actually
 
TheRandomGuy7 said:
With 3x front intakes and 1x extra intake on the bottom, it doesn't seem like a bad idea - I'm guessing this shifts the airflow to more bottom --> top as opposed to the more traditional front --> back
Click to expand...
Keep in mind case can only flow the lesser volume area of intake and exhaust. If you have 5x 140mm intakes and only 2x 140mm exhaust vents, case only flow as much air as can flow out the 2x 140mm exhaust vents. Simple airflow displacement / physics; equal and opposite action ; case can only flow as much air in as is flowing out
 
doyll said:
Keep in mind case can only flow the lesser volume area of intake and exhaust. If you have 5x 140mm intakes and only 2x 140mm exhaust vents, case only flow as much air as can flow out the 2x 140mm exhaust vents. Simple airflow displacement / physics; equal and opposite action ; case can only flow as much air in as is flowing out
Click to expand...

This is why I like ths idea of an extra top exhaust, even if it is usually seen as a disruptor to airflow.

With 4x intake fans I do want enough air being exhausted and this is 10x as important with a GPU like a 3080, which pumps out an insane 350W of heat that needs to get out ASAP.

I think I'll be keeping the 2x top and 1x rear exhaust setup, run these 3 exhausts at a silent 45-50% rpm and run the 4 intake fans a bit faster at 60% or so. This seems to give excellent airflow, excellent results, and very low noise levels.
 
Airflow is a bit of a black art. What works for one case can fail miserably in another. So many factors play in the final outcome.
In general driving air in to the case is great, but then it has to get out. The only reason you need an exhaust fan is not to exhaust the air as such, because it will happily find it's own way out, but to ensure that you set up a flow over vital pieces of equipment. No good if all your air goes out the bottom of the case and only a fraction is traveling past the CPU for example. The problem with front fans mixed with top fans is that you might be drawing air out and creating a flow that is actually bypassing everything important. Especially the top fan at the front.
 
TheRandomGuy7 said:
This is why I like ths idea of an extra top exhaust, even if it is usually seen as a disruptor to airflow.

With 4x intake fans I do want enough air being exhausted and this is 10x as important with a GPU like a 3080, which pumps out an insane 350W of heat that needs to get out ASAP.

I think I'll be keeping the 2x top and 1x rear exhaust setup, run these 3 exhausts at a silent 45-50% rpm and run the 4 intake fans a bit faster at 60% or so. This seems to give excellent airflow, excellent results, and very low noise levels.
Click to expand...
It is physically impossible to flow more air in than out / out than in. While stacking fans as intake on one side and exhaust on other generally doesn't make much if any difference, it sometimes changes flow channels / paths thus supplying cooler air where needed. But as pp111 says, it's 'a bit of black art'. It takes time to monitor airflow changes by recording air temp in different places while changing component load and/or fan / fans speed, then comparing data to determine what will hopefully improve overall performance with lower temps and noise levels.

pp111 said:
Airflow is a bit of a black art. What works for one case can fail miserably in another. So many factors play in the final outcome.
In general driving air in to the case is great, but then it has to get out. The only reason you need an exhaust fan is not to exhaust the air as such, because it will happily find it's own way out, but to ensure that you set up a flow over vital pieces of equipment. No good if all your air goes out the bottom of the case and only a fraction is traveling past the CPU for example. The problem with front fans mixed with top fans is that you might be drawing air out and creating a flow that is actually bypassing everything important. Especially the top fan at the front.
Click to expand...
Exactly right!

For me the best way to setup case airflow is monitoring air temp entering components I want running cooler. They playing with fan speed and placement until I get best temps and noise results.

What I've found is almost all tower builds work best with front full on good pressure rated intakes, all opening in front (maybe front half of case) not filled with fans block off so air fans push into case has to flow on through case, not leak into front and go in circles. Almost always removing all PCIe back slot covers improves back vent area, thus improve front to back airflow, thus lower fan speed and lower temps. Sometimes a bottom intake will help supply cool air to GPU, but need to be careful it's not pushing too much air in with can end up pushing GPU heated exhaust up into path of CPU cooler's cool intake airflow.

Best low cost remote sensor thermometers I've found are the cheap indoor/outdoor digital ones with wired remote probes/sensors. If probes are metal I tape them up so they can't short out in running systems. A cloths pin on a piece of stiff insulated wire can be twirsted / taped to probe lead so probe can be positioned in middle of airflow into cooler fans.

Then monitor and record temps and fans speeds adjusting fan (both case & component fans) speeds until optimum balance for best airflow with low noise and temps is found. Usually I run out of patients settling for what is expectable rather than optimum. Doesn't really matter if it's optimal if it's acceptable. ;)
 
rumple9 said:
I've thought about it but worried my case would end up full of dust when comp is not on
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My son's case with top fans has a magnetic dust cover that sits on top. I tend to remove it when the PC is being used for gaming though so as not to impede airflow.

Generally top exhaust just makes logical sense to me, the heat should be rising up so you want to pull cold air in lower down and then expel the hottest air. I accept it's not quite that simple though i.e. you might end up with some air coming in the front getting pushed out too quickly rather than flowing through the rear exhaust.
 
I have seen tests where a top exhaust fan infront of the cpu cooler is worse as it removes some air that would otherwise go through the cpu air cooler. Certainly though top exhaust fans at the cpu cooler or further back is very effective.

In fact in systems (which use a air cpu cooler) where the are three 120mm fans roof positions - I would use the first one as an intake (to blow air down into the case and infront of the cpu cooler) and the back 2 fans as exhaust (to suck out the warm air that exits from the cpu cooler).
 
Case designers design more for looks than good airflow. Best tower case airflow is front to back, but look at how many have no front fan vents, or have venting area a small fraction of fan area.
140mm fan has about 130sq mm 15386
Vent grills restrict airflow by about 70%, so a 140x140mm vent has 60sq mm of airflow area.
​
Ideally our fans should have open area same distance as their diameter in front of them to pull air from .. nost have 20-30mm not 140mm. ;)

Simply put, few (maybe no) cases are really designed for good airflow.
 
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