Question Ordered 4-pin PWM case fan: not sure if I should use CPUFAN2 header or sys_fan1

Dec 29, 2020
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Hi all,

I'm replacing the rear exhaust fan that came with my case, as I suspect the bearing is bad. This fan is connected into the CPUFAN2 header, and has been for the past 4 years.

The new fan I am getting is 4-pin PWM. I looked in my MOBO manual, and the sys_fan1 slot is NOT PWM, whereas the CPUFAN2 slot is. Does that mean, on its own, that I should plug my new fan in the CPUFAN2 slot? I have read conflicting answers.

Thank you
Please note I am using MSI X99A SLI PLUS motherboard
 
Hi all,

I'm replacing the rear exhaust fan that came with my case, as I suspect the bearing is bad. This fan is connected into the CPUFAN2 header, and has been for the past 4 years.

The new fan I am getting is 4-pin PWM. I looked in my MOBO manual, and the sys_fan1 slot is NOT PWM, whereas the CPUFAN2 slot is. Does that mean, on its own, that I should plug my new fan in the CPUFAN2 slot? I have read conflicting answers.

Thank you
Please note I am using MSI X99A SLI PLUS motherboard
If you plug it in CPUFAN_2 header it's more than likely it will adjust speed according to CPU temperature while SYS_Fans take commands from another sensor on MB.
Only problem you may run into is it may interfere with CPU cooler fan, either making them run at some speed that is between CPU and that fan depending on how CPU_Fan 1 and 2 are connected in BIOS. if they have separate entries In BIOS, you could control them independently.
 

Paperdoc

Glorious
Ambassador
I recommend you plug this rear exhaust fan into the mobo SYS_FAN1 header, even though it may have only 3 pins and uses only the older Voltage Control Mode. That header bases its automatic fan control function on a temperature sensor on the mobo, which is best for case ventilation fans. The 4-pin PWM fan design includes a backwards compatibility feature for use in this way. It will receive no PWM signal from the non-existent Pin #4 and hence cannot modify the flow of power from the source on Pin #2 through the motor. BUT the VOLTAGE of that source will be varied to accomplish motor speed changes, so it will work.
 
Reactions: CountMike
Dec 29, 2020
5
0
10
0
I recommend you plug this rear exhaust fan into the mobo SYS_FAN1 header, even though it may have only 3 pins and uses only the older Voltage Control Mode. That header bases its automatic fan control function on a temperature sensor on the mobo, which is best for case ventilation fans. The 4-pin PWM fan design includes a backwards compatibility feature for use in this way. It will receive no PWM signal from the non-existent Pin #4 and hence cannot modify the flow of power from the source on Pin #2 through the motor. BUT the VOLTAGE of that source will be varied to accomplish motor speed changes, so it will work.
Thanks for the reply doc. I went into my BIOS and saw that SYS_FAN1 header was set to "CPU" option for "Temp Select Source". I changed it to "SYSTEM". I also enabled Smart Fan Control. I reckon that's what needed to be done.

I also noticed that CPUFAN2 header could be set to "System". Would it make sense to then use that slot, in this case, considering it's PWM AND can be set to System as Temp Source?

Thanks so much
 
Dec 29, 2020
5
0
10
0
If you plug it in CPUFAN_2 header it's more than likely it will adjust speed according to CPU temperature while SYS_Fans take commands from another sensor on MB.
Only problem you may run into is it may interfere with CPU cooler fan, either making them run at some speed that is between CPU and that fan depending on how CPU_Fan 1 and 2 are connected in BIOS. if they have separate entries In BIOS, you could control them independently.
Thanks for the quick reply.
CPUFAN1 and 2 indeed have separate entries in the BIOS. They are both using the CPU as the temp source. I also noticed that SYS_FAN1 was using the CPU as its temp source.. I changed it to "System", thoughts?
 

madmatt30

Titan
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That's good either way. With air cooling CPU and GPU largely determine case temperature.
Some people actually prefer to set case fan speeds to cpu temps, it allows case fans to ramp up/slow down with actual system usage.

With a 4 pin fan AND header its irrelevant whether fans are same size or different rpm speeds because pwm signals translate to percentages speed wise of each fan.

There is no actual right or wrong imo, it's entirely up to the user to decide
 
Dec 29, 2020
5
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Some people actually prefer to set case fan speeds to cpu temps, it allows case fans to ramp up/slow down with actual system usage.

With a 4 pin fan AND header its irrelevant whether fans are same size or different rpm speeds because pwm signals translate to percentages speed wise of each fan.

There is no actual right or wrong imo, it's entirely up to the user to decide
Makes sense.
I noticed my current fan (which im replacing very soon) is a lot louder when it’s plugged in the SYS_FAN1 header. And I made sure the speed settings are the same in the bios, so idk what’s up with that. My SYS_FAN1 header also doesn’t support PWM. Still unsure if I should plug my new exhaust fan it into CPUFAN2 or Sys_Fan1
 

madmatt30

Titan
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Your board ssecs are stating 2 x 4 pin cpu fan headers and 3 x 4 pin system fan headers.

Is this info wrong??

Irregardless you are over thinking it a little imo.

I do actually have my exhausts tied into cpu temps as I'm running a 140mm fan on the cpu cooler and 140mm case fans, they're good enough at low rpm to give good case cooling at low system usage and I like the silence it affords me.

They virtually only ramp up when the system is under gaming use at which point I dont care so much about noise because I have gaming sounds blasting out of my speakers

Like I said, there is nor right and wrong, some people are happy with fans running 100% all the time, I'm obsessed with silence myself to the point of stupidity🤣

What's you case and cooling setup in its entirety??
 

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