optimal case fan config?

polonyc2

Fully [H]
Joined
Oct 25, 2004
Messages
19,032
my new case has room for 3 140mm front fans, 3 140mm top, 2 140mm bottom and 1 140mm rear...all fans can also be configured with 120mm case fans

is there an optimal number of fans for best cooling?...does more equal better or does it eventually hit diminishing returns?...what's the best setup?...I'm assuming 2 front intake and 1 rear outtake at a minimum...should I use 140mm throughout or a mix of 140 and 120mm?
 

pendragon1

Fully [H]
Joined
Oct 7, 2000
Messages
23,452
140s, 2 in, 2 out should be good. if you are water cooling, i would use the rear as intake and then 3 up top for exhaust. gives the vrm more fresh air.
edit: you can also up the number of fans and decrease speed/noise a bit.
 
Last edited:

polonyc2

Fully [H]
Joined
Oct 25, 2004
Messages
19,032
140s, 2 in, 2 out should be good. if you are water cooling, i would use the rear as intake and then 3 up top for exhaust. gives the vrm more fresh air.

I'm not doing any water cooling...so 2 intake, 1 rear exhaust and 1 top exhaust?...neutral air pressure?...I always thought positive air pressure was best (more air coming in)?...I've always liked using top exhaust fans as heat rises so it makes sense
 

pendragon1

Fully [H]
Joined
Oct 7, 2000
Messages
23,452
I'm not doing any water cooling...so 2 intake, 1 rear outtake and 1 top outtake?...neutral air pressure?...I always thought positive air pressure was best (more air coming in)?...I've always liked using top outtake fans as heat rises so it makes sense
k. sounds fine. yeah i try to balance it or slightly more in. i have 120x2 front and 1 back and 140x2 top.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
I've found good hi-pressure rated front intakes (3x in your case) with all back PCIe slot covers removed to increase rear vent area around GPU, block all opening in front half of case not covered by intake fans so air they are flowing into case has to move on through case to go out, (not leak around in front of fans and go in circles) and no exhaust fans are needed. Using both intake and exhaust fans is like using push/pull on radiator or cooler. It might improve temps by a degree or two, but only at full speed because more fans make more noise. Slow them down to same noise level as case with only intake fans and temps are the same, maybe a little warmer. Only time intake and exhaust improve cooling is at full speed and then only by a couple degrees. If you are like me (and most others) our fans rarely if ever run full speed. ;)

Below link is basic guide to how airflow works and how to optimize case airflow:
https://hardforum.com/threads/basic-guide-to-improving-case-airflow.1987938/
 

d3athf1sh

Gawd
Joined
Dec 16, 2015
Messages
737
personally i use all available slots. front and bottom would be intakes rear and top exhaust. all 140's. that would also give you some positive pressure to help with dust bunnies.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
personally i use all available slots. front and bottom would be intakes rear and top exhaust. all 140's. that would also give you some positive pressure to help with dust bunnies.
Assuming you have even 1 less exhaust than intake fans you r case will end up negative pressure and draw dust in any openings not filtered exhaust fans. Reason is front grills are more restrictive than exhaust, plus filters make them even more restrictive.

Also keep in mind the amount of pressure differential our computer fans make is very, very little .. like about as much difference in pressures as there is on our feet and on our chest standing at sea-level. Yeah, that's not much difference .. and if you don't believe me do the calculations to find out how little pressure differential 1.5mm H2O really is.
 

SmokeRngs

[H]ard|DCer of the Month - April 2008
Joined
Aug 9, 2001
Messages
16,811
I'd go all front 140mm fans for intake and a single exhaust fan in the rear. You want this to make sure you get as much cool air coming into the case which is reasonable and creates airflow across a large volume of the case front to back. The exhaust fan is next to the CPU and VRMs which are some of the hottest components and something you want airflow around. It also allows for direct removal of some of the hottest air in the case. In my experience not having a case fan exhausting the hot air out of the case by the CPU increases CPU temps by 2C-5C.

I don't know that I'd even bother with fans on the bottom of the case. Those are the fans most likely to end up pushing dust into the case which is annoying at best. It can also negatively affect airflow and airpaths. More airflow isn't always a good thing if the extra airflow is disrupting the path of the airflow from the front to the back of the case.

Fans at the top of the case can also cause similar problems but there are some advantages which may offset the issue. I have a single fan at the top of my case used as intake. It happens to be at the spot which blows directly across the VRMs and CPU heatsink. It does not help cooling the CPU but it does keep the VRMs a bit cooler and allows for a little extra airflow for the RAM. My case has 5.25 bays which one of them is used so I don't have an intake fan on the front of the case to blow across those components which is a factor in how I have my cooling setup.

The full intake setup as 140s on the front with a single exhaust is the starting point. It's not going to hurt to have a couple extra fans and experiment with placing them in the other spots your case has for fans to see whether they help, hinder or simply don't affect cooling.
 

freeagentt

Limp Gawd
Joined
Dec 5, 2018
Messages
145
No it really doesn't matter, dust is going to get in. If its in your house, it'll be in your case, the way you move the air does not matter because the air is moving already.. like a dirty river.

Just had a look at the link, nice.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
In normal home with 2 adults, not pets or kids in southern England filtered intakes w/ only intake fans keeps almost all dirt out of system. Oldest system is over 4 years with a little dust showing in a few places.
In normal home 2 adults 2 pets (dogs) in central Montana similar systems collected about 3 times as much dust / dander / hair.

Key to filters working well is hovering / vacuuming them every couple of weeks and fans running 10-50% speed 90% of time and almost never above about 80%. Slower airflow through filters catches dust much better than when airflow is fast. ;)
 

pendragon1

Fully [H]
Joined
Oct 7, 2000
Messages
23,452
the environment difference between england and montana could the the only difference needed for extra dust. totally different...
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
That was the point of giving information about dust accumulation in different environments.

Systems in both environments stay clean. Computer In dryer / more dirt / animal dander environment needs filters cleaned more often and inside every year or two while other needs less often filter cleaning and can go years without collecting enough dust to need cleaning.

I think most of owners are somewhere between the above environments and if system airflow is setup similar to what I do won't have a serious dust problem.
 

pendragon1

Fully [H]
Joined
Oct 7, 2000
Messages
23,452
That was the point of giving information about dust accumulation in different environments.

Systems in both environments stay clean. Computer In dryer / more dirt / animal dander environment needs filters cleaned more often and inside every year or two while other needs less often filter cleaning and can go years without collecting enough dust to need cleaning.

I think most of owners are somewhere between the above environments and if system airflow is setup similar to what I do won't have a serious dust problem.
england is not dusty dry ass montana, less dust to begin with, invalid comparison imo. did op ask about dust? no.
 

polonyc2

Fully [H]
Joined
Oct 25, 2004
Messages
19,032
with a negative airflow more dust will accumulate which is why I try to either stay with positive or neutral airflow...with my current case setup I have 2 front intakes, 2 fans over the GPU area, 2 top exhaust and 1 rear exhaust

with my new case I have space for fans at the bottom but as SmokeRngs said it might interfere with the airflow of the other fans...
 

mnewxcv

Supreme [H]ardness
Joined
Mar 4, 2007
Messages
7,601
I would do 3x140mm front, 1 140mm rear, 2 140mm top (toward rear) and call it a day. balanced pressure, and more fans means same airflow at lower noise when compared to fewer fans.
 

polonyc2

Fully [H]
Joined
Oct 25, 2004
Messages
19,032
I would do 3x140mm front, 1 140mm rear, 2 140mm top (toward rear) and call it a day. balanced pressure, and more fans means same airflow at lower noise when compared to fewer fans.

I thought more fans meant more noise?
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
I thought more fans meant more noise?
More fans is more noise, even at idle.

Level increase Δ L for
n equal loud sound sources​
Number of n equal loud sound sources​
Level increase
Δ L in dB​
1​
0​
2​
3.0​
3​
4.8​
4​
6.0​
5​
7.0​
6​
7.8​
7​
8.5​
8​
9.0​
9​
9.5​
10​
10.0​
12​
10.8​
16​
12.0​
20​
13.0​

http://www.sengpielaudio.com/calculator-spl.htm

And it's not just the fans adding noise, but also the noise of air flowing to / from each fan through grill, filter, etc.
 

mnewxcv

Supreme [H]ardness
Joined
Mar 4, 2007
Messages
7,601
More fans is more noise, even at idle.

Level increase Δ L for
n equal loud sound sources​
Number of n equal loud sound sources​
Level increase
Δ L in dB​
1​
0​
2​
3.0​
3​
4.8​
4​
6.0​
5​
7.0​
6​
7.8​
7​
8.5​
8​
9.0​
9​
9.5​
10​
10.0​
12​
10.8​
16​
12.0​
20​
13.0​


http://www.sengpielaudio.com/calculator-spl.htm

And it's not just the fans adding noise, but also the noise of air flowing to / from each fan through grill, filter, etc.
that is true of equally loud sound sources as it says. However, if you have 6 fans instead of 4, they don't have to spin as fast to do as much work, and should be quieter in theory. Even based on that chart the difference between 4 and 6 would be 1.8dB. Would be an interesting test to see just how loud the difference is at load though. I have 2 140mm and 3 120mm noctua fans in my case and they are silent at idle, but can definitely hear them if they get to their 1700RPM max speed. They sound pretty pleasant up to about 1200 though which is where I have them set to hangout unless temps are climbing like crazy in a p95 or 100% load render scenario.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
Under load, to move the same amount of air, more fans will spin at a lower rpm than fewer fans. Most fans are quieter and lower rpm.
Actually that is not true. While speed of fan does affect it's ability to draw or push air through grill, fins, filter etc. running more fans does not change how fast air flows through those same vents and filters. So if airflow is same though each vent, adding more fans in case or adding exhaust fans doesn't change how much air is flowing though that vent .. and that is same amount of air that is flowing through the case. In a case the air intakes pull air into case flowing it on through case and out.

Adding fan to exhaust vent only marginally increases flow by creating a push/pull from intake/exhaust vents. 2x fans in push pull don't have higher airflow, but because push/pull increases (doubles) fan pressure rating it is easier for push/pull to overcome resistance. This is true of push / pull on radiators and coolers, but not much if any with intake / exhaust fans on our cases. With good pressure rated fans it makes almost no difference to have both intake and exhaust fans. Obviously low pressure rated fans can't do a good job regardless of how many are used.

We need to keep in mind air flow is very similar to water flow. If we think of our computer case as a box van under water with vents being open windows in fan. Now think of propellers in windows pushing water into and out of van as fans in case moving air in out of case. We can't move more water into van than is flowing out. Propellers moving water into van cannot move more water in than is flowing out of van. Same with out cases. So if van has 8 windows and we put fans in 4 windows, maximum flow through van is 4 window worth of moving water. Again, same applies to our cases.

Hopefully that helps with understanding how airflow works.

I've spent most of my life working with airflow, from air cooled engines, automotive and race engine intake and exhaust flow, combustion chamber flow patterns, etc. I'm not just making this all up.

Also keep in mind computer fans we use create extremely little pressure differential from intake side to exhaust side. 1.5mm H2O pressure rating (difference in pressure from intake side to exhaust side of fan) is about the same difference as the pressure of air on your feet and on your chest at sea level. Think I'm crazy? Look it up and calculate if for your self and you will find out I'm right.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
that is true of equally loud sound sources as it says. However, if you have 6 fans instead of 4, they don't have to spin as fast to do as much work, and should be quieter in theory. Even based on that chart the difference between 4 and 6 would be 1.8dB. Would be an interesting test to see just how loud the difference is at load though. I have 2 140mm and 3 120mm noctua fans in my case and they are silent at idle, but can definitely hear them if they get to their 1700RPM max speed. They sound pretty pleasant up to about 1200 though which is where I have them set to hangout unless temps are climbing like crazy in a p95 or 100% load render scenario.
That's true, but we need to add the noise created by airflow through grills, etc. They create much more of an increase in dB than fan itself does .. and indeed fan under load is louder as well. Indeed, 1200rpm is definitely audible, but not obnoxious .. at least with good fans. Personally I prefer fans below 1000rpm. Very few of my builds have fans running faster than 1000-1100rpm except in extreme conditions .. like hot summer day with dirty filters, or pushing old i7 920 @ 4.3GHz overclock at 100% load stress test.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
You have the right to express your opinion, same as I do. Do you know enough about fluid dynamics to understand how much of it does or does not apply? My experience is not just cars, but all kinds of airflow / fluid dynamics, aerodynamics, as well as computers from Commodore and first IBM personal computer to current models .. for as long as we've had personal computers. Although not much additional airlfow on really old ones. ;)
 

TheSlySyl

Gawd
Joined
May 30, 2018
Messages
732
I have 3x 140mm intake, 3x 140mm exhaust (two top, one rear) and another 120mm slim fan exhaust (under the GPU - it unusual but it works.) I have yet another 140mm on my CPU. All of them are set to a super low RPM and my case is literally silent unless the GPU spins up under load. I could have kept that silent as well if I was willing to deal with a bit of throttling.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
I have 3x 140mm intake, 3x 140mm exhaust (two top, one rear) and another 120mm slim fan exhaust (under the GPU - it unusual but it works.) I have yet another 140mm on my CPU. All of them are set to a super low RPM and my case is literally silent unless the GPU spins up under load. I could have kept that silent as well if I was willing to deal with a bit of throttling.
Are you monitoring airflow temps into coolers? Hard to know what temp air they are using without having a probe in front of their cooler fans. It's possible that if you were to increase intake fan speed GPU would receive lower temp air and run cooler .. because every degree cooler air entering cooler is becomes same degrees cooler component is at same fan speed and load. ;)
 

TheSlySyl

Gawd
Joined
May 30, 2018
Messages
732
Yes. I know that increasing intake fan speed would lead to lower GPU temps, but that also leads to more noise - something I'm absolutely not willing to tolerate.

I've done tests, forcing my GPU fans to 100% does not change any temps or performance so I'm pretty sure I have a good balance going on. increasing the case intake/exhaust RPMs is only a super minor temp change for CPU.
I have a lot of components in my case that need to be cooled (6x HDD and 4x NVME SSDs.)

However, most of my use cases that require perfect silence do not, at the moment, require heavy GPU usage.

It's not that my GPU runs hot or is "loud", it's just that it's literally the only component in my PC that makes a *sound* at all.
 

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
Considering 1080 is rated 250w and 3900 is rated 105w, so it's possible even with overclock GPU could be making as much or more heat than CPU is, and pushing it through a smaller cooler as well.
 

TheSlySyl

Gawd
Joined
May 30, 2018
Messages
732
Considering 1080 is rated 250w
My 1080Ti actually peaks around 300watts and usually stabilizes around 270-280w. I've had it stable as high as 330watts but the tradeoffs were very much not worth it.

I have one of the models that has dual 8 pin connectors.
 
Last edited:

doyll

[H]ard|Gawd
Joined
Feb 4, 2012
Messages
1,284
My 1080Ti actually peaks around 300watts and usually stabilizes around 270-280w. I've had it stable as high as 330watts but the tradeoffs were very much not worth it.

I have one of the models that has dual 8 pin connectors.
Didn't realize you had it OC'ed that much! Really making lots of heat!
 
Top