[SOLVED] What should be the temperature source for case fans?

Aug 13, 2022
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Relevant components:
  • Case: modded Thermaltake VG200 with its front panel removed: there is now a mesh filter in front of the fans
  • Intake front fans: 3x Arctic P12 PWM PST CO
  • Exhaust rear fan: 1x stock Thermaltake
  • Motherboard: MSI B450 Gaming Plus Max
Presently the three Arctic fans are daisy chained to a single pin and set up in the BIOS as "PWM", while the temperature source is "CPU Core"; however, I didn't set a custom fan curve for them.

Are there any recommended BIOS settings for case fans? Is the CPU the correct temperature source?
 
Last edited:

Paperdoc

Polypheme
Ambassador
Most mobos have two (sometimes more) temperature sensors used to guide fans. There is always the sensor inside the CPU chip and that always is used for the CPU_FAN header (and CPU_OPT if you have that). There is always a CHA_FAN or SYS_FAN header (often more than one) and these MAY offer to let you use different temp sensors built into the mobo. Some mobos have only one such sensor often called System or Motherboard, and this is best to guide any case ventilation fans you have. That general mobo fan is placed at the spot that the makers decided is most representative of the whole mobo, OR near the component with the greatest need for cooling, and the default fan curve for that header is set for that mobo area. Many mobos also include a couple of additional sensors like in the Voltage Regulator area or the Southbridge chip. These are of use mainly if you set up one fan aimed at that particular mobo component and dedicate one fan header to control cooling of that particular area.

Every video card has its own means of cooling, most as a fan system powered and controlled internally by the card itself. There never has been any standard way for the TEMPERATURE of the video card (normally, of its GPU chip) to be fed back to the mobo. So there is NO way for the mobo to find that signal and offer it to the user as a temp measurement source. Commonly the software utility provided with the graphics card does show that temp to you because its makers knew how to find it, and so you can use that yourself as a way to MANUALLY set some fan's header speed. Alternatively SOME third-party software utilities know how to find that info for a range of different graphics cards and CAN use that for automatic control of a mobo-connected fan.

In your case, you have three intakes on the front and one exhaust at rear. Front fans are PWM (4-pin) type, rear fan is 3-pin older style requiring DC Mode for speed control. Since the methods of controlling speed are different from these two types, they should be connected to different headers, which I think you have done. Your mobo has four SYS_FAN headers, and they are configured by default to use DC Mode. The header where you have the three front PWM fans connected should be configured to PWM Mode. The header for the rear 3-pin fan should be set to DC Mode, and then you can have its speed controlled automatically if you choose.

You have not talked about your CPU cooler, but I presume it is connected to the CPU_FAN header which will use the CPU chip's internal sensor for guidance. For all of your (front and rear) case fans the best temp sensor to use will be the SYSTEM (general mobo) sensor. Those fans provide air to cool everything in the case, mobo and all. Even the CPU gets that air source (unless you have a radiator drawing directly from outside), but its system makes adjustments to flow of that air over the CPU according to the CPU temperature.

IF you want to increase cooling capacity of your system slightly, I'd suggest one additional fan as exhaust, probably at the top rear location. It can be plugged into an unused SYS_FAN header and configured to use this same temp sensor and either DC Mode (for 3-pin fan) or PWM Mode (for 4-pin).
 
What is your goal?

Lowest possible temps with no concern for noise?

Something else?

Are you willing to experiment with fan curves?

Normally.....I'd try to connect each fan to an individual connector and control each with individual fan curves if available. You may not have enough connectors?
 
Aug 13, 2022
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What is your goal?

Lowest possible temps with no concern for noise?

Something else?

Are you willing to experiment with fan curves?

Normally.....I'd try to connect each fan to an individual connector and control each with individual fan curves if available. You may not have enough connectors?
To give you an idea, the CPU cooler's fans are set to run at 20% speed at 40c, ramping up to 100% at 70c. In other words, acceptable levels of noise at lower loads, but I don't care if it sounds like a jet engine at higher temps.

The board has enough pins, but this particular case is terrible to work with. Does daisy chaining the fans cause issues?
 
I've never daisy chained. I use 3 case fans and always ensure that my boards have 3 fan connectors.

I'd think your fan curve idea is in the ballpark. Low rpm in the interest of low noise unless under a big load....which ideally isn't very often.

My fans are low noise/quiet to begin with, so I use something more like 50% until temps hit 60 and full throttle at 70 degrees.

95% of the time my fans are at 500 rpm and cannot spin above 1200 regardless. But I don't have significant heat issues and don't use a video card at all.

You can fiddle with settings and ideas as much as you care to....depending on your anxiety level about temps generally and your noise tolerance. I have low anxiety over temps and am somewhat averse to noise.
 
Aug 13, 2022
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I've never daisy chained. I use 3 case fans and always ensure that my boards have 3 fan connectors.

I'd think your fan curve idea is in the ballpark. Low rpm in the interest of low noise unless under a big load....which ideally isn't very often.

My fans are low noise/quiet to begin with, so I use something more like 50% until temps hit 60 and full throttle at 70 degrees.

95% of the time my fans are at 500 rpm and cannot spin above 1200 regardless. But I don't have significant heat issues and don't use a video card at all.

You can fiddle with settings and ideas as much as you care to....depending on your anxiety level about temps generally and your noise tolerance. I have low anxiety over temps and am somewhat averse to noise.
I guess I can copy-paste the CPU fans' curve to the case fans. Thing is, I don't know what the temperature source for the case fans should be, as there are multiple options, including "CPU Core" and "System".
 
I guess I can copy-paste the CPU fans' curve to the case fans. Thing is, I don't know what the temperature source for the case fans should be, as there are multiple options, including "CPU Core" and "System".
I just checked my own BIOS.

My case fans have 2 choices on what to monitor: CPU or motherboard.

They are both set to motherboard. I can't recall ever spending any time researching the right choice. Did it on an "off the top of my head" guess.

You might be able to drill into your motherboard's specs and find out exactly where your "system" sensors are.

But I'd guess there is only a very slim chance that the choice you make would make a significant difference in your computing life......I suppose it might if you had an unusual situation where you put extreme loads on CPU or video card for extended periods of time and were constantly generating a lot of heat.
 
I just checked my own BIOS.

My case fans have 2 choices on what to monitor: CPU or motherboard.

They are both set to motherboard. I can't recall ever spending any time researching the right choice. Did it on an "off the top of my head" guess.

You might be able to drill into your motherboard's specs and find out exactly where your "system" sensors are.

But I'd guess there is only a very slim chance that the choice you make would make a significant difference in your computing life......I suppose it might if you had an unusual situation where you put extreme loads on CPU or video card for extended periods of time and were constantly generating a lot of heat.

Try both for a week and evaluate the differences in noise level?
 
I bought an NZXT fan controller because I don't like how your only options for temperature source at the UEFI level is either the CPU or the motherboard (which I presume is the chipset). Neither of these output enough heat in my system to be of concern. The fan controller allows me to adjust the case fans based on the video card temperature, which during gaming I find is more important to monitor and adjust the fans for. To put in perspective, the CPU dissipates maybe around 40-50W. The GPU on the other hand will easily dissipate 3-4 times that amount. I think I'd rather have my cooling based on the hottest part of the system.

Plus I can adjust the fan speeds while in Windows and running a load to find a sweet spot between fan noise and component temperature.

Of note, NZXT CAM which you need to configure the fan controller can also run without elevated privileges. I haven't tried Corsair's iCUE recently, but Corsair is the only alternative I'm aware of that has a fan controller and last I used iCUE, it required elevated privileges to run.
 
Are there any recommended BIOS settings for case fans? Is the CPU the correct temperature source?
if your board's BIOS only offers CPU or System as the base source you may want to look into some motherboard control software that may allow other sensors to be read and included.

it will usually be different for every setup;
different case layout, different fan models, different GPU & CPU generating more heat than average, etc.

for the passed 10 years or so i have kept separate fans with separate profiles with some blowing cooler air into my GPUs and others carrying cooler air towards/through my CPU coolers.

a few of my latest builds have been setup with;
bottom & front-bottom intake fans and rear exhaust based on GPU temperature,
front-mid/top fans aimed more toward the radiator or CPU heatsink will be based on CPU temp.

my latest build uses a hub for grouping my front 3x intakes to a single header that are reading my CPU temperature to keep a nice cool quiet wall of air flowing towards the top-mounted radiator and across other components.
my bottom intake and rear exhaust are based on GPU temp with a higher fan curve in place.
 

emitfudd

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I guess most cases don't have a fan controller built in? I have two cases that both have one. I leave my case fans on high all the time on my gaming rig and low on my backup pc.
 
I guess most cases don't have a fan controller built in? I have two cases that both have one. I leave my case fans on high all the time on my gaming rig and low on my backup pc.
Three cases I've used in builds have had a built-in fan controller. But two of them could only generously be called that (it was basically a "hi/low" switch). The other one came with an NZXT controller, and I bought just the controller for my current build.

I'm also under the impression most built-in fan controllers are incredibly simple. I need something with automation and software control so I don't have to think about it.
 
I'm also under the impression most built-in fan controllers are incredibly simple. I need something with automation and software control so I don't have to think about it.
any nicer higher quality case should come with a nice fan hub or fan/LED combo hub.

all the last versions i've used;
be quiet! Dark Base 700,
Silent Base 802,
Corsair iCUE 220,
Fractal Design Vector RS,
Zofos,
and a couple others that have escaped my memory included a PWM fan hub that would either connect to a front I/O button or directly to a motherboard header for software control.

if the motherboard in use doesn't offer control software that can control the PWM headers,
maybe look into better motherboards?
 
any nicer higher quality case should come with a nice fan hub or fan/LED combo hub.

all the last versions i've used;
be quiet! Dark Base 700,
Silent Base 802,
Corsair iCUE 220,
Fractal Design Vector RS,
Zofos,
and a couple others that have escaped my memory included a PWM fan hub that would either connect to a front I/O button or directly to a motherboard header for software control.

if the motherboard in use doesn't offer control software that can control the PWM headers,
maybe look into better motherboards?
So as a reference point, I have a Fractal Design Meshify C with 2x140mm fans in the front and a 1x120mm fan in the back. My motherboard is an ASRock B550 Steel Legend.
  • A fan hub is pretty worthless to me because most motherboards have enough headers for the amount of fans I have. And even then I could just use a Y-splitter.
  • I already mentioned that motherboards only have the CPU or the board itself as the temperature input. This is not adequate for me because when gaming, which is the most common load I put on it, the hottest thing is the video card. I would rather adjust the fans based on the temperature of that, not the CPU or the motherboard. And I'd rather not rely on the video card warming up the rest of the system to heat up the main input so that the fans start working harder.
  • I've tried the motherboard manufacturer's fan control utility, but it doesn't work. SpeedFan also doesn't work.
So the solution I've settled on, as I put in my previous post, is NZXT's fan controller with NZXT CAM. Why?
  • NZXT CAM doesn't need admin privileges to run (I'm very weary of programs that need it)
  • NZXT CAM also has a guest mode (at least for now)
  • I can do all of my adjustments while in Windows, while doing something
  • I can create and swap between profiles depending on what I'm doing.
 
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Thank you everyone for the exhaustive replies. I don't presently own a fan controller, so for the time being I've set identical curves for both the CPU cooler's fans and the intake fans, setting the CPU as the temperature source for all of them.

The fan curve is the "performance" one recommended by Arctic: 20% speed from 0 to 40c, then slope to 100% at 70c.

The only exception is the rear exhaust fan, which is DC and not PWM. I haven't touched its settings since I assenbled this pc, the BIOS merely says "7.20V". I guess I'll be replacing it soon.

However, it would be probably better to set the case fans to the GPU's temperature instead, but the sources other than CPU are only "System", "PCH" and "MOS"; would there be any software comparable to MSI Afterburner when it comes to case fans?
 
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Karadjgne

Titan
Ambassador
There's 3 main sources for temps. Cpu (core/package/socket) , gpu, motherboard (case). If you have software like SpeedFan or Rem0o or the very few others with that capability, it'll be able to setup exactly which sensor reports to which area, which fan header etc. And those are interchangeable, set them as you desire.

There's no correct way or setting to temp sensors, use what you will or can and change fan curves accordingly.

My pwm pump is set for liquid temps from a thermal coupler, as is 1 set of rad fans, the other set of rad fans (I have 2 rads) is set by cpu temp. This keeps my temps where I want them, within reason.
 
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Paperdoc

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Most mobos have two (sometimes more) temperature sensors used to guide fans. There is always the sensor inside the CPU chip and that always is used for the CPU_FAN header (and CPU_OPT if you have that). There is always a CHA_FAN or SYS_FAN header (often more than one) and these MAY offer to let you use different temp sensors built into the mobo. Some mobos have only one such sensor often called System or Motherboard, and this is best to guide any case ventilation fans you have. That general mobo fan is placed at the spot that the makers decided is most representative of the whole mobo, OR near the component with the greatest need for cooling, and the default fan curve for that header is set for that mobo area. Many mobos also include a couple of additional sensors like in the Voltage Regulator area or the Southbridge chip. These are of use mainly if you set up one fan aimed at that particular mobo component and dedicate one fan header to control cooling of that particular area.

Every video card has its own means of cooling, most as a fan system powered and controlled internally by the card itself. There never has been any standard way for the TEMPERATURE of the video card (normally, of its GPU chip) to be fed back to the mobo. So there is NO way for the mobo to find that signal and offer it to the user as a temp measurement source. Commonly the software utility provided with the graphics card does show that temp to you because its makers knew how to find it, and so you can use that yourself as a way to MANUALLY set some fan's header speed. Alternatively SOME third-party software utilities know how to find that info for a range of different graphics cards and CAN use that for automatic control of a mobo-connected fan.

In your case, you have three intakes on the front and one exhaust at rear. Front fans are PWM (4-pin) type, rear fan is 3-pin older style requiring DC Mode for speed control. Since the methods of controlling speed are different from these two types, they should be connected to different headers, which I think you have done. Your mobo has four SYS_FAN headers, and they are configured by default to use DC Mode. The header where you have the three front PWM fans connected should be configured to PWM Mode. The header for the rear 3-pin fan should be set to DC Mode, and then you can have its speed controlled automatically if you choose.

You have not talked about your CPU cooler, but I presume it is connected to the CPU_FAN header which will use the CPU chip's internal sensor for guidance. For all of your (front and rear) case fans the best temp sensor to use will be the SYSTEM (general mobo) sensor. Those fans provide air to cool everything in the case, mobo and all. Even the CPU gets that air source (unless you have a radiator drawing directly from outside), but its system makes adjustments to flow of that air over the CPU according to the CPU temperature.

IF you want to increase cooling capacity of your system slightly, I'd suggest one additional fan as exhaust, probably at the top rear location. It can be plugged into an unused SYS_FAN header and configured to use this same temp sensor and either DC Mode (for 3-pin fan) or PWM Mode (for 4-pin).
 
Aug 13, 2022
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That general mobo fan is placed at the spot that the makers decided is most representative of the whole mobo, OR near the component with the greatest need for cooling, and the default fan curve for that header is set for that mobo area.
Extremely helpful reply. I only have one question: there doesn't appear to be a default fan curve when setting to PWM or DC; both run at 60% all the time.

A curve only appears when checking the "smart fan curve" option, which I used to make a custom curve for the CPU cooler, an Arctic Freezer 34 eSports Duo (following Arctic's recommendation for a "performance" curve from their own manual, which is 20% from 0 to 40c, sloping to 100% at 70c).

Is it ok to just leave the case fans spinning at 60% all the time, or is the default smart fan curve from the mobo generally good enough?
 
Is it ok to just leave the case fans spinning at 60% all the time, or is the default smart fan curve from the mobo generally good enough?
Only downside would be noise or possibly wearing out the fan quicker than if spinning at a lower rate. Case fans could die at any moment regardless....just like any other component.

Your personal tolerance for noise and your personal anxiety level regarding temps come into play.
 

Paperdoc

Polypheme
Ambassador
First, thanks for Best Solution.

The on-line manual for your mobo does not show any details of what its configuration options are in Hardware Monitor, so I can only write about "typical" items. One is the MODE - that is, the type of electrical signals the header sends to the fan to control its speed. Normally these include Voltage Control Mode (aka DC Mode), and PWM Mode. DC Mode is for 3-pin fans, PWM for 4-pin fans. Then there's a PROFILE choice for how the system makes the decision of what the speed should be. These normally include "Standard" or "Normal" which uses a default "fan curve" of speed (actually, a % of full power) versus TEMPERATURE measured at the relevant sensor, whether the details of that curve are shown or not; "Turbo" for constant full speed; "Quiet" for constant slow speed; and "Custom" in which you get to specify your own "fan curve" for automatic control based on temperature. Sometimes there's an overlap in terms here. Some systems use the display of the fan curve both to show you what it will do by default and to allow you to move those points to create your custom curve. Some will use the label "Manual" in place of "Custom" to indicate that this lets you manually set the fan curve. Others may use the term "Manual" for an option that lets you specify one fixed speed (not the same as Turbo or Quiet). This last sounds like what you have done - one fixed speed all the time. On other systems that use a custom-specified fan curve, you can accomplish virtually the same thing by specifying the SAME speed for all temperatures.

That "Smart Fan Curve" option sounds like what I called "Standard" - that is, it uses a default "fan curve" that DOES alter the fan speed according to temperature. You used that for the CPU cooler. Is the same option available on your SYS_FAN headers? If so, use that for them, and verify that these headers are using the motherboard temp sensor, not the one in the CPU chip.

You SHOULD have the fan speeds adjusted for you automatically according to temperature. That way they will run fairly slowly when your workload is low, and speed up for heavy workloads. Using a fixed speed may mean the fan noise is low, but YOUR comfort with noise should NOT be the aim. The aim should be the TEMPERATURE of your system components so they are cooled properly at all times and last longer. In extreme cases of high workloads with inadequate cooling by slow fans, the system MAY get so hot it slows itself down to protect it. Then you have MUCH reduced performance so your fan can keep quiet - not a common strategy!

In general, and especially when starting out, I suggest the default fan curve is the right choice. Consider the alternative: how do you decide what IS a better choice? You do not have any info on what the real temperatures are over MANY mobo components, nor of what those SHOULD be. In that case, some try for extra caution and set a custom curve to do MORE cooling than the default at all temperatures. The only downside to that is VERY slightly less lifetime for fans you CAN replace after several years. But setting it for LESS cooling than default I consider risky.
 
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Is it ok to just leave the case fans spinning at 60% all the time, or is the default smart fan curve from the mobo generally good enough?
no one can tell you that without knowing what temperatures your system is hitting in each mode, what average temperatures you would like it to remain around, and what type of noise the fans are producing vs what you would like to hear.

it's up to you to experiment with the different settings and decide which noise ratio vs temperature setting is best for your situation.
 
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First, thanks for Best Solution.

The on-line manual for your mobo does not show any details of what its configuration options are in Hardware Monitor, so I can only write about "typical" items. One is the MODE - that is, the type of electrical signals the header sends to the fan to control its speed. Normally these include Voltage Control Mode (aka DC Mode), and PWM Mode. DC Mode is for 3-pin fans, PWM for 4-pin fans. Then there's a PROFILE choice for how the system makes the decision of what the speed should be. These normally include "Standard" or "Normal" which uses a default "fan curve" of speed (actually, a % of full power) versus TEMPERATURE measured at the relevant sensor, whether the details of that curve are shown or not; "Turbo" for constant full speed; "Quiet" for constant slow speed; and "Custom" in which you get to specify your own "fan curve" for automatic control based on temperature. Sometimes there's an overlap in terms here. Some systems use the display of the fan curve both to show you what it will do by default and to allow you to move those points to create your custom curve. Some will use the label "Manual" in place of "Custom" to indicate that this lets you manually set the fan curve. Others may use the term "Manual" for an option that lets you specify one fixed speed (not the same as Turbo or Quiet). This last sounds like what you have done - one fixed speed all the time. On other systems that use a custom-specified fan curve, you can accomplish virtually the same thing by specifying the SAME speed for all temperatures.

That "Smart Fan Curve" option sounds like what I called "Standard" - that is, it uses a default "fan curve" that DOES alter the fan speed according to temperature. You used that for the CPU cooler. Is the same option available on your SYS_FAN headers? If so, use that for them, and verify that these headers are using the motherboard temp sensor, not the one in the CPU chip.

You SHOULD have the fan speeds adjusted for you automatically according to temperature. That way they will run fairly slowly when your workload is low, and speed up for heavy workloads. Using a fixed speed may mean the fan noise is low, but YOUR comfort with noise should NOT be the aim. The aim should be the TEMPERATURE of your system components so they are cooled properly at all times and last longer. In extreme cases of high workloads with inadequate cooling by slow fans, the system MAY get so hot it slows itself down to protect it. Then you have MUCH reduced performance so your fan can keep quiet - not a common strategy!

In general, and especially when starting out, I suggest the default fan curve is the right choice. Consider the alternative: how do you decide what IS a better choice? You do not have any info on what the real temperatures are over MANY mobo components, nor of what those SHOULD be. In that case, some try for extra caution and set a custom curve to do MORE cooling than the default at all temperatures. The only downside to that is VERY slightly less lifetime for fans you CAN replace after several years. But setting it for LESS cooling than default I consider risky.
Extremely helpful reply, wish you could list two answers as the best ones. In the end I switched the case fans' temperature sources to "System" and enabled their default smart fan curves, which predictably ended up making the PC quieter as it generally doesn't heat up much in the first place. Will have to test with something more demanding in the future. Thanks again!
 

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