Air-cooling principles - several questions from a novice builder

Coolio

n00b
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Jan 8, 2021
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47
Dear community,

I'm thinking of my first build these days, and will highly appreciate if you find a minute to comment on the following:

  1. Does the cooling (be it air or AIO) work non-stop since the PC is switched on, but the intensity of fans/pump (and noise level, respectively) changes with the workload (e.g. office apps vs. games)?
  2. To decrease noise level (be it air or AIO) does it make sense to go for a low FPI (fins per inch) radiator (<8 FPI) specifically designed for low speed fans?
  3. Is it right, that increasing the size of intake/outtake case fans won't slow down RPM of the CPU heatsink fan? So if I want to decrease CPU fan's noise level I should replace it with a bigger one (which has higher TDP and thus - lower RPM)?
Thank you guys!
 

lopoetve

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31,183
1. Generally yes, for most systems and configurations. This can be overridden if desired.
2. I'll let someone else answer this.
3. Depends on what you mean. If you have more cool air coming in, the CPU will be cooler, and based on 1, likely running the fan slower. To a point, mind you - there's generally a minimum set speed too. Bigger CPU fans tend to run slower and thus quieter too, but as always, "it depends" - you can get high flow high-speed big fans too, and they can be noisy.
 

rgMekanic

[H]ard|News
Joined
May 13, 2013
Messages
5,457
Dear community,

I'm thinking of my first build these days, and will highly appreciate if you find a minute to comment on the following:

  1. Does the cooling (be it air or AIO) work non-stop since the PC is switched on, but the intensity of fans/pump (and noise level, respectively) changes with the workload (e.g. office apps vs. games)?
  2. To decrease noise level (be it air or AIO) does it make sense to go for a low FPI (fins per inch) radiator (<8 FPI) specifically designed for low speed fans?
  3. Is it right, that increasing the size of intake/outtake case fans won't slow down RPM of the CPU heatsink fan? So if I want to decrease CPU fan's noise level I should replace it with a bigger one (which has higher TDP and thus - lower RPM)?
Thank you guys!

1 yes, on most motherboards or in software the CPU fan speeds will be temperature dependant.

2 yes. Higher fpi radiators have the potential to cool more due to more surface area to disapate the heat. However it requires a fan that has more static pressure to overcome the resistance of the fins, which are generally louder, coupled with more "wooshing" of the air through the fins.

3 ambient temperature is a low as you can possibly go in conventional cooling. But that is the ambient temperature around the cpu cooler/radiator. If it's 90f inside the case, 90f is as cool as that cpu is going to get, and, due to more advanced things, will cause the cpu to get even hotter. Cooler you get the case, the less work the cpu cooler will need to do, and the cooler theoretical temps achievable. I go with large, high airflow fans for case fans in the attempt to keep case ambient close to room ambient, while remaining quiet
 

TheSlySyl

[H]ard|Gawd
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May 30, 2018
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I have 4 different types of fans in my case and each one is set to different fancurves by the PWM on the motherboard. You can usually get as precise as you want per fan these days.
 

Coolio

n00b
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Jan 8, 2021
Messages
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Thank you all guys, it was a real pleasure to read your replies - a lot of useful info and those smart details to learn, great! 👍

This can be overridden if desired.
Just to make sure - are you talking about CPU fan or case fans? My bad that I didn't clarify this point in the question itself, but I rather meant case fans, as I assume CPU fan works in a non-stop mode... Why/when may one wish to override - what do you get in return to this stress of the system?

However it requires a fan that has more static pressure to overcome the resistance of the fins, which are generally louder
Yep, sounds reasonable. Am I right assuming that higher pressure fans are smaller by themselves, as their work is to concentrate max. airflow to a certain point, so at the end of the day there are 2 reasons why they're loud: higher RPM and smaller size of blades?
By the way, when we're talking about low-FPI radiators we mean CPU cooling, as case fans don't have radiator at all, right?

I go with large, high airflow fans for case fans in the attempt to keep case ambient close to room ambient, while remaining quiet
Bigger CPU fans tend to run slower and thus quieter too
Well, looks like the silver bullet for silence lovers is "go for as bigger fans as you can" (for both CPU and the case). Is that the point? I mean if you can plug 80mm or 120mm, forget about the former and start comparing dB within the 120mm range that fits your budget, is that the logic?

I have 4 different types of fans in my case and each one is set to different fancurves by the PWM on the motherboard.
there's generally a minimum set speed too
TheSlySyl Are there any specific requirements to the fan or MoBo to have a control you're talking about? I know 4-pin (vs. 3-pin) non-Molex connector is a mandatory thing for both fan and MoBo, but are there any other requirements?
By the way, do you manage this control on the BIOS level, or on the app one?

lopoetve Is the minimum speed a spec which is factory set (and thus - hardwired)? Should I pay attention to it when narrowing the range of fans to consider?


Thank you guys, appreciate your support!
 

TheSlySyl

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I have an Asrock X570 Taichi that has 4x 4pin fan controllers and a CPU/waterpump header, so I just have all the fans plugged into the mobo.

I use the BIOS because A-tune app is a little more finicky than the bios one. I mostly go by sound in my situation. I take a set of fans, put them as high as I can that's totally silent, then build the rest of the curb from there. Knowing that my CPU is gonna max out around 80c. However that's also only if I'm hammering it super hard with a transcoding job.
My CPU fan is basically 100% all the time because it's quiet no matter what, and the most noticeable fan is the weird little 120mm slim exhaust fan, so its curb is actually less aggressive. Can't stand the sound it makes at full, but its also the least effected by CPU temp.
I also have the X570 chipset fan to be on silent full time from the same bios settings.

My GPU fan, however, is controlled by Afterburner. Which I've been doing for over a decade now.
 

JSHamlet234

Weaksauce
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Apr 9, 2021
Messages
66
This is my procedure for a main 24/7 rig (i.e. not a bench rig):

1) Get the room to the hottest conceivable temperature it will ever get to (generally 30C for me).
2) Set all fans to 100%
3) Do all stress testing at that ambient temperature and set clocks/voltages accordingly.
4) Record the maximum CPU temperature reached at the 24/7 O/C settings.
5) Set the fans to ramp up gradually starting at 40C and up until about 15 degrees below the Max temp (from 20% to 60% fan speed).
6) Set fans to ramp up more rapidly from 60-100% between 15 and 5 degrees below the max temperature.

If you do it this way, you'll have a machine that is as quiet as possible, but your cooling capacity will always increase when necessary, and you won't have crashes because the seasons changed, or your AC broke. Just my 2c
 

Nobu

Supreme [H]ardness
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You may need more radiator if you get a low fpi rad and run your fans slow, depending on how much heat you need to move from cpu/gpu/etc. This will need to be determined by you once you figure out what parts you will be using in your system, and what you will be cooling with your loop.
 

DoubleTap

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2,702
As others have said, most aspects of cooling are interconnected - a high fpi heatsink will extract more heat, but may require more static pressure (ie: more noise) to lose the heat.

One other dimension to keep in mind is size.

You can make a pretty compact, high performance system these days, but as a rule of thumb, your fans are going to work harder and you're going to hear them more.

I like small systems, but I like quiet systems even more - most of the time you can trade an increase in size for a decrease in noise by getting a bigger cooler (Noctua DH15) or a triple slot / hybrid GPU or by adding more/bigger radiators

I went all in on this tradeoff - massive, massive radiator capacity with very slow fans for extremely low noise.

Oh - bigger often costs more too, so there is that...
 

Coolio

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TheSlySyl well, dude, quite a System you got I should say! (y) Looking at Taichi occasionally myself.. Having your own usecase by now - do you recommend?

If you do it this way, you'll have a machine that is as quiet as possible, but your cooling capacity will always increase when necessary
Wow, an impressive and solid approach. Is that what they call "fan curve building"? Am I right your step-by-step guide may be adopted for any fan, MoBo, heatsink size/FPI, etc.?

You may need more radiator if you get a low fpi rad and run your fans slow
I went all in on this tradeoff - massive, massive radiator capacity with very slow fans for extremely low noise.
I'm ready for any even weird action the sub-10L case allows. ;)

Guys, is there any rule of a thumb to define the number of case fans I need? Any specific balance between intake/outtake ones?

Thanx!
 

TheSlySyl

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I love my x570 taichi, but my use case requires stability and a LOT of hard drive space. It's overkill for most builds and probably not the best choice if you're going for a lean performance based PC, but it's been fantastic for my use case.

This is extremely general - but you usually want a roughly equal intake and exhaust, with maybe a little more intake so that you suck in less dust. (Positive pressure)
If they're super unbalanced then some of your fans basically won't be doing anything.
 

Coolio

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TheSlySyl Well, my usecase will be office work 60% of time and gaming 40%, maybe video processing in the future (which is likely to be the next build's "problem"). So looks like I'll not beat the sh*t out of this machine. But just out of curiosity - what's the connection between the use scenario and HDD space? :eek:

Good point about the positive pressure, noted! To call an intake/outtake story a day: what are the best practices of case fan positioning in sub-10L cases (e.g. FormD T1, Louqe Ghost S1, Dan A4)? Front/back, top/bottom - what are the pros and cons to be aware of?

Thank you!
 

Fire-Fox

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Guys, is there any rule of a thumb to define the number of case fans I need? Any specific balance between intake/outtake ones?
Personally i prefer equal intake - exhaust or a little more intake, depending the Case i have/buy.
I own a Corsair Obsidian 1000D and have x8 front intake x3 top exhaust and x2 rear exhaust.
 

TheSlySyl

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TheSlySyl Well, my usecase will be office work 60% of time and gaming 40%, maybe video processing in the future (which is likely to be the next build's "problem"). So looks like I'll not beat the sh*t out of this machine. But just out of curiosity - what's the connection between the use scenario and HDD space? :eek:

Good point about the positive pressure, noted! To call an intake/outtake story a day: what are the best practices of case fan positioning in sub-10L cases (e.g. FormD T1, Louqe Ghost S1, Dan A4)? Front/back, top/bottom - what are the pros and cons to be aware of?

Thank you!
Raw 4k video takes up a LOT of space, as does hosting my own media server. Combination of the two puts me at around 45 filled TB out of my 52 usable at the moment. My system is available to/is transcoding probably a good 50% of the time. I'm also transcoding while gaming these days as I'm having fun messing around on Twitch, for games that my system can handle doing both simultaneously at least. (I still can't do certain games, like Cyberpunk, without lowering the Image Quality beyond a respectable amount. Damn you GPU Bottleneck!)

Video processing can and will take 100% of every single thread your CPU has to throw at it. Gaming will do the same with your GPU, its rare that both are at 100% load simultaneously, but certain games definitely get close, especially if you're trying to stream with software encoding. Though that usually leads to encoding framerate drops.
 

JSHamlet234

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Wow, an impressive and solid approach. Is that what they call "fan curve building"? Am I right your step-by-step guide may be adopted for any fan, MoBo, heatsink size/FPI, etc.?

Yes, once you've chosen your components, that's how to dial them in.

As I look over what I wrote, I do want to add one thing - the maximum temperature you tune the fan curves for should be based on the stress test that is the hardest to pass (i.e. needs the most CPU core voltage to pass). That is often, but not always the hottest test. For example In my main rig, the hardest test to pass is Prime 95 v.30.4 Large FFT, specifically 8192K FFT length. The hottest test is Prime Small FFT, but I can pass that one with about 15mV less than what I need for large FFT. Therefore I tune for 100% fan speed at the max temp in Large FFT, not small FFT.
 

DoubleTap

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TheSlySyl well, dude, quite a System you got I should say! (y) Looking at Taichi occasionally myself.. Having your own usecase by now - do you recommend?


Wow, an impressive and solid approach. Is that what they call "fan curve building"? Am I right your step-by-step guide may be adopted for any fan, MoBo, heatsink size/FPI, etc.?



I'm ready for any even weird action the sub-10L case allows. ;)

Guys, is there any rule of a thumb to define the number of case fans I need? Any specific balance between intake/outtake ones?

Thanx!
There isn't really a rule of thumb because every case and every fan and every system is different. A lot of more recent cases have been designed to hide the fans behind glass with small vent for intake/filtration. I think this trend is slowly giving way as people go back to airflow focused cases but you have to think at the system level, not the component level. Most people prefer "positive pressure" meaning more intake than exhaust as the minor pressure differential means the air escapes through all the little holes in the case - negative pressure can result in dust getting into every little opening due to a slight vacuum effect.

This is my Ncase M1 with dual MORA3 420 radiators, each using four (4) Noctua 200mm fans. The excessive radiator surface means the fans can run silent (400rpm) about 90% of the time and usually only spin up (still basically silent at around 60%) when the room warms up (lowering the system to ambient temp delta and making cooling less efficient). This system can play games with the fans off for at least 15 minutes before the >1 Gallon of coolant hits 41C and triggers the alarms.

(this system was originally going to be three fan-less MORA3 420 rads and may or may not have been based on a dare)

1620225585118.png
 

TheSlySyl

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Due to requiring steady sound and silence over anything else, i actually keep my fans at a lower RPM until I hit about 65c (usually only happens during full load). That way when I'm messing with audio in post production, i don't have to worry about the background noise changing (from my computer at least.)
It's not computationally "optimal" but it IS optimal in my situation.

Those MORA3 420 radiators look awesome.
 

Nasgul

Weaksauce
Joined
Jun 11, 2005
Messages
96
Dear community,

I'm thinking of my first build these days, and will highly appreciate if you find a minute to comment on the following:

Thank you guys!
It all can be summarized as:
-If you're going air-cooling (heat-sink/fan) get a be quiet! Dark Rock Pro 4 or Noctua NH-D15 for high-end.
-Going with AIO, 280mm or 360mm models would yield the best results, just don't cheap out on the brand. Nickel-plated CPU blocks are better.

The rest is just too much technical data that changes or not from brand to brand and user to user. Like buying a car, you won't know it till you drive it.
 
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