System Fan Into CPU Fan Header?

[VicariousStudio]

Hello everyone.So I currently have a Cooler Master N400 with an MSI x99a Gaming 7 Motherboard. This motherboard has 2 CPU Fan Headers, and 3 SYS Fan Headers. I have 4 case (system) fans total. I am using a Corsair H100i for cooling the CPU so I only need 1 CPU Fan header. So my question is, are there any issues with plugging the 4th System fan into the currently unused CPU Fan header? I do realize this would mean its RPM would be listed as "CPU2" in temps. I do not wish to invest in a fan controller at this time so the other alternative is to plug it directly into power and have it run wide open all the time. Any information would be appreciated, thanks all.

[Josephdalepi]

Just now, VicariousStudio said:

Hello everyone.So I currently have a Cooler Master N400 with an MSI x99a Gaming 7 Motherboard. This motherboard has 2 CPU Fan Headers, and 3 SYS Fan Headers. I have 4 case (system) fans total. I am using a Corsair H100i for cooling the CPU so I only need 1 CPU Fan header. So my question is, are there any issues with plugging the 4th System fan into the currently unused CPU Fan header? I do realize this would mean its RPM would be listed as "CPU2" in temps. I do not wish to invest in a fan controller at this time so the other alternative is to plug it directly into power and have it run wide open all the time. Any information would be appreciated, thanks all.

itll be fine

its what ive been doing for a long time

[unidentical]

Fan header is a fan header. There are 2 reasons they're labeled. 1: so you can identify what's connected in the BIOS. 2: most motherboards will throw a warning if a cpu fan isn't plugged in as a safety feature. So they just label it cpu_* to make it clear what's expected to go there.

[VicariousStudio]

Just now, unidentical said:

Fan header is a fan header. There are 2 reasons they're labeled. 1: so you can identify what's connected in the BIOS. 2: most motherboards will throw a warning if a cpu fan isn't plugged in as a safety feature. So they just label it cpu_* to make it clear what's expected to go there.

Right and thank you. Doesn't this mean however, that the RPM of the Case fan plugged into the CPU Header will be controlled by the CPU Temp rather than the case temp? Sorry I'm not all too familiar with how that worked, I assumed the CPU fans revved up when the CPU was hotter and the SYS fans revved up when the case temp was hotter. And since, in my case, the CPU is water cooled, I was worried that it may not make use of the case fan in CPU2 header. Am I incorrect in thinking this?

[unidentical]

2 minutes ago, VicariousStudio said:

Right and thank you. Doesn't this mean however, that the RPM of the Case fan plugged into the CPU Header will be controlled by the CPU Temp rather than the case temp? Sorry I'm not all too familiar with how that worked, I assumed the CPU fans revved up when the CPU was hotter and the SYS fans revved up when the case temp was hotter. And since, in my case, the CPU is water cooled, I was worried that it may not make use of the case fan in CPU2 header. Am I incorrect in thinking this?

I haven't run a fan on anything other than min rpm for years, but from what I recall most fan curves will go off CPU temp as there aren't a lot of boards that have multiple temperature sensors. CPU temps are the best indication the board will have anyway, as the ambient temp rises so will the CPU temp because a cooler will typically provide x degrees below ambient.

So as internal temps rise, so will cpu and if a fan curve is specified, your fan rpm will increase accordingly.

A possible exception is if you have a water cooler that draws air directly from outside the case.

[danomicar]

Interesting. I always thought the fan types had differed in some way.

[VicariousStudio]

Just now, unidentical said:

I haven't run a fan on anything other than min rpm for years, but from what I recall most fan curves will go off CPU temp as there aren't a lot of boards that have multiple temperature sensors. CPU temps are the best indication the board will have anyway, as the ambient temp rises so will the CPU temp because a cooler will typically provide x degrees below ambient.

So as internal temps rise, so will cpu and if a fan curve is specified, your fan rpm will increase accordingly.

A possible exception is if you have a water cooler that draws air directly from outside the case.

Ah ok. My rad fans blow out and not in so that wont be an issue. Would you recommend then, using the CPU header over running it directly to power?

Just now, mcfly said:

Interesting. I always thought the fan types had differed in some way.

Same here @mcfly. Actually my line of thinking was, since my CPU was water cooled, it wouldn't be as much of a factor as the GPU was. And since it's really my GPU that will be putting heat into the case mostly (It is neither water cooled nor external exhaust) I was kind of hoping that a system/case temp would tell my case fans when to bring in more cool air.

[VicariousStudio]

I believed there were 2 separate sensors, 1 for CPU and 1 for "Motherboard" as shown here: *Note, this isnt my image, but it matches my motherboards bios.

[unidentical]

3 minutes ago, VicariousStudio said:

I believed there were 2 separate sensors, 1 for CPU and 1 for "Motherboard" as shown here: *Note, this isnt my image, but it matches my motherboards bios.

2 sensors it is. At any rate, ambient temps will still increase CPU so binding one system fan to that header isn't going to make much of a difference. You're probably using at least 120mm fans which push plenty of air. 

For reference look at my specs. I have that running with a single intake fan, 180mm running so slow I can't hear it same with the one fan on the cooler. No other system fans. No temperature issues when gaming or editing video.

[VicariousStudio]

Cool, and nice setup by the way :). Mine is listed in my profile, dont know how to make if feed into my signature like you have, but that's awesome! Actually I have 2x120mm fans intake in the front, 1x120mm fan in the rear exhaust, 2x120mm top exhaust (Through radiator), and 1x120mm intake in the side for a total of 6x120mm fans. I reasoned that with 3 in and 3 out, but 2 of the 3 exhaust being through a rad that would be slightly positive pressure which I wanted, and the side fan blows directly on the gpu so that is a plus. I would love to see more data on that as well, I realize ambient temps must effect the cpu temp, but with the cpu being water cooled I wonder how that changes that or if it changes it at all.

[unidentical]

https://www.pugetsystems.com/labs/articles/How-Ambient-Temperatures-Affect-Your-PC-158/

 

It's linear. Regardless of cooler. Linus and tiny Tom both have videos that go in to detail on this, couldn't find them. You'll see in that article that the CPU and gpu fans will spin as hard as they can to try to keep the temps in check but as ambient temp rises, the processor temps follow the same line. In the oc3d cooler reviews they always sort by delta for this reason, rather than average temp.

[LogicalDrm]

7 hours ago, VicariousStudio said:

Right and thank you. Doesn't this mean however, that the RPM of the Case fan plugged into the CPU Header will be controlled by the CPU Temp rather than the case temp? Sorry I'm not all too familiar with how that worked, I assumed the CPU fans revved up when the CPU was hotter and the SYS fans revved up when the case temp was hotter. And since, in my case, the CPU is water cooled, I was worried that it may not make use of the case fan in CPU2 header. Am I incorrect in thinking this?

 

All fans are by default controlled by CPU temp. Most mobos don't have option to select which sensor is being used as base. As mobo doesn't really need extra cooling (passive airflow is enough), they just have sensor for temps but nothing really connected to it.

 

CPU2/CPU_OPT is usually using same controller chip with CPU header. Which means that you rarely can control them separately. It will follow with you pump.

System fans aren't by default controlled by anything. They will just blow at full or almost full speed until you setup curve for them manually.

[VicariousStudio]

Awesome, thank you