Intake or exhaust fan - a test.

[yiplong]

I always wondered whether it is better to use only exhaust fans or to use a mix of exhaust and intake fans, so I did a test.

Original set up:

- one 120mm rear exhaust
- one 120mm top exhaust
- one 120mm side intake fan
- Xigmatek S1283 blowing up

The temps are:

CPU idle: 31, load: 45
GPU idle: 52, load: 78

then I changed the 120mm side intake fan to "top exhaust", now I have 1 rear exhaust and 2 top exhaust, with no intake fan.

The temps are:

CPU idle: 29, load: 41
GPU idle: 50, load: 75-76

So at least in my case having all exhaust cools better than a mix of exhaust and intake fans. Note that I have two side air vents, when all 3 exhaust fans were used, they created enough suction that a napkin would stick to these side vents. In a case with no side vents, it may not work so well.

The drop in CPU temp was expected, what surprised me was the drop in GPU temp. I put that intake fan on the side specifically to help cool the GPU. So I guess my original set up was harming it rather than helping.

 

[treefrog07]

Looks like you came up with a better confguration. What are your system components? What case? What fans are you using?

 

[yiplong]

Looks like you came up with a better confguration. What are your system components? What case? What fans are you using?

Components:

- P2 X3 720 4thcore unlocked@3.6ghz
- Ga-MA770T-UD3P mobo
- 1 HDD, no optical drive
- MSI Radeon 5750

The case is NZXT Evo Beta and the two top exhaust fans are these:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103022&cm_re=coolermaster_case_fan-_-35-103-022-_-Product
The rear exhaust fan came with the case, although it was originally mounted in the front. Since I need no cooling for the HDD, I moved it to the rear when I put this rig together.
I am actually thinking about replacing one of the two CoolerMaster fans with one of these:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835233036&cm_re=xigmatek_140mm-_-35-233-036-_-Product
it is 140mm, moves more air (63 vs 30 cfm) and seems quieter than the CoolerMaster, then I can either junk the spare fan or use it as front intake. This may reduce the temp even further allowing me to push the OC higher. What do you think?

 

[randomkid]

I think the fact that you move the fan to that top is what caused the improvement since it help to take out hot air outside the case. Warm air naturally goes up but without the 2nd top fan, some of it may hover on part that have no fan. Putting the 2nd fan ensures all the warm air is sucked out from the top.

If you have the extra 120mm it will be nice to see how the temperature will be if you put back a 120mm intake on one of the side holes while keeping 2 fans working on the top.

By the way, those are already cool temps in any case. I only got a Xigmatek SD-964 and my CPU temp goes up to 51 during Prime95 test on Helios 910 case. The fan on the SD-964 spins at 2200rpm. How about your S1283?

 

[jsc]

You are neglecting the PSU fan in your considerations. Admittedly, it's a constant, but you still need to consider it.

 

[yiplong]

I think the fact that you move the fan to that top is what caused the improvement since it help to take out hot air outside the case. Warm air naturally goes up but without the 2nd top fan, some of it may hover on part that have no fan. Putting the 2nd fan ensures all the warm air is sucked out from the top.

If you have the extra 120mm it will be nice to see how the temperature will be if you put back a 120mm intake on one of the side holes while keeping 2 fans working on the top.

This is an interesting scenario for sure. Then we know whether having a side intake fan harms or improves general airflow. My prediction is it will make no difference, particularly if the side fan is low-noise, low-cfm. When I have another 120mm fan, I will slap it on the side panel and see what happens. But then, we have a 4fan vs. 3fan situation, it is kind of not fair.

By the way, those are already cool temps in any case. I only got a Xigmatek SD-964 and my CPU temp goes up to 51 during Prime95 test on Helios 910 case. The fan on the SD-964 spins at 2200rpm. How about your S1283?

I think the S1283 fan has 3 speeds, about 300, 600 and 1100 depending on cpu temp.

 

[JofaMang]

In my experience, the lower side fan should always be an exhaust fan. Regardless of the rest of the system, pulling warm air directly away from the GPUs prevents that heated air from warming the rest of the system. I now use 2x 120mm exhaust fans (side and back) and a 120mm intake up front. I have direct tunnel intake tube running to my top mounted CPU fan, which is not air tight, but close enough short of actually sealing it to the CPU fan.

When I first installed my side mount 120, I tried blowing on the GPU. The results were an increase in both GPU and CPU temps, iirc, the GPU was at 60c/95c, and the CPU 40c/62c, and this was with without any OC on the parts.

Turning the side mount to exhaust (the only change to the system) dropped my GPU to 45/75c, and CPU to 21/44, overclocked. At stock speeds, the CPU was running 19/26c, and the GPU 42/71c with this side mount exhausting.

In my specific situation, with my non reference sapphire card (slight venting out the back, lots of heat put into case) exhausting out the side was the only answer to my thermal issues.

 

[yiplong]

In my experience, the lower side fan should always be an exhaust fan. Regardless of the rest of the system, pulling warm air directly away from the GPUs prevents that heated air from warming the rest of the system. I now use 2x 120mm exhaust fans (side and back) and a 120mm intake up front. I have direct tunnel intake tube running to my top mounted CPU fan, which is not air tight, but close enough short of actually sealing it to the CPU fan.

When I first installed my side mount 120, I tried blowing on the GPU. The results were an increase in both GPU and CPU temps, iirc, the GPU was at 60c/95c, and the CPU 40c/62c, and this was with without any OC on the parts.

Turning the side mount to exhaust (the only change to the system) dropped my GPU to 45/75c, and CPU to 21/44, overclocked. At stock speeds, the CPU was running 19/26c, and the GPU 42/71c with this side mount exhausting.

In my specific situation, with my non reference sapphire card (slight venting out the back, lots of heat put into case) exhausting out the side was the only answer to my thermal issues.

That's a very interesting insight you have there. My setup is a little different. I have no intake fan and just 2 top exhaust, 1 rear exhaust. I will get side fan and try it both as exhaust and intake and see what happens.