[SOLVED] What's the best 120mm rear exhaust fan I can get my hands on?

ProtoflareX

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Jan 3, 2014
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Originally, I was planning to buy a case that supported a 140mm rear exhaust fan, and I planned to buy a Noctua NF-A14 to fill that slot. However, I recently decided to purchase a different case instead which does not support a 140mm rear exhaust fan, but a 120mm one instead. I'm now looking for a 120mm fan that rivals the NF-A14 in performance to fill that 120mm rear exhaust slot. Based on my research, the two options I've found so far that seem like they would accommodate my needs are the following fans:

  1. Cooler Master Masterfan Pro 120 Air Flow
  2. Be Quiet! Silent Wings 3 High Speed 120mm PWM
I looked at some of Noctua's 120mm offerings, but even their latest and greatest NF-A12x25 has a lower CFM than the two options I listed above. Additionally, I know that if I wanted "the best", one of Noctua's industrial fans would be the right choice, but I'm looking for a 120mm fan that operates at an acceptable noise level while simultaneously rivaling the NF-A14 in performance. Would one of the two fans I mentioned above do the trick? Or is there an even better fan out there that I'm unaware of?
 

Karadjgne

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Herald
Hard question to answer. Realistically nobody ever runs their fans at full 100%, and that includes the rear exhaust. So exact cfm at full speed becomes pointless numbers. A decent 140mm will move more cfm than a comparable 120mm, but that doesn't mean the fan isn't as good, just means you are stuck with 120mm fans that will move a decent amount of air at acceptable noise.
In order to better answer, you'd need the flow charts like Noctua has for performance across the rpm spectrum and not many make those. Fan A might have better cfm at 50% rpm than fan B, but fan B might have better cfm at 100%rpm. That's all in the blade design, rpm etc.

So you will not get a 120mm fan that rivals a 140mm exactly, or even very close, but you can get decent performance at 120mm and its not all shown by cfm numbers at max rpm. Any of those listed are decent, pick the one that's cheaper or looks better.
 

Karadjgne

Titan
Herald
Hard question to answer. Realistically nobody ever runs their fans at full 100%, and that includes the rear exhaust. So exact cfm at full speed becomes pointless numbers. A decent 140mm will move more cfm than a comparable 120mm, but that doesn't mean the fan isn't as good, just means you are stuck with 120mm fans that will move a decent amount of air at acceptable noise.
In order to better answer, you'd need the flow charts like Noctua has for performance across the rpm spectrum and not many make those. Fan A might have better cfm at 50% rpm than fan B, but fan B might have better cfm at 100%rpm. That's all in the blade design, rpm etc.

So you will not get a 120mm fan that rivals a 140mm exactly, or even very close, but you can get decent performance at 120mm and its not all shown by cfm numbers at max rpm. Any of those listed are decent, pick the one that's cheaper or looks better.
 

ProtoflareX

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Jan 3, 2014
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Hard question to answer. Realistically nobody ever runs their fans at full 100%, and that includes the rear exhaust. So exact cfm at full speed becomes pointless numbers. A decent 140mm will move more cfm than a comparable 120mm, but that doesn't mean the fan isn't as good, just means you are stuck with 120mm fans that will move a decent amount of air at acceptable noise.
In order to better answer, you'd need the flow charts like Noctua has for performance across the rpm spectrum and not many make those. Fan A might have better cfm at 50% rpm than fan B, but fan B might have better cfm at 100%rpm. That's all in the blade design, rpm etc.

So you will not get a 120mm fan that rivals a 140mm exactly, or even very close, but you can get decent performance at 120mm and its not all shown by cfm numbers at max rpm. Any of those listed are decent, pick the one that's cheaper or looks better.
Your comment brings to mind a question I've always had about fans. Assuming that a fan is voltage controlled and not PWM controlled, what conditions would make the fan run at 100% speed?
 
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Karadjgne

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Herald
Temps. Depends entirely on the fan curves, duty cycle you set in bios or software. You can set the fans to max out at any temp above the lowest duty cycle which is usually 30° / 60%. You can even disable control and set for a constant speed.

Analog and pwm work totally differently, good analog start at 5v-12v (40% to 100%) and are constantly fed that voltage according to the duty cycle. Pwm are constant 12v, but the pwm signal turns the fan on/off in cycles. The longer the on cycle, faster the fan spins, then off, then on etc. But both work towards the same purpose, certain rpm range according to the bios/software instructions. Higher the sensor reported temp, the faster the pwm cycles or the higher the voltage.
 
Last edited:

ProtoflareX

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Jan 3, 2014
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Temps. Depends entirely on the fan curves, duty cycle you set in bios or software. You can set the fans to max out at any temp above the lowest duty cycle which is usually 30° / 60%. You can even disable control and set for a constant speed.

Analog and pwm work totally differently, good analog start at 5v-12v (40% to 100%) and are constantly fed that voltage according to the duty cycle. Pwm are constant 12v, but the pwm signal turns the fan on/off in cycles. The longer the on cycle, faster the fan spins, then off, then on etc. But both work towards the same purpose, certain rpm range according to the bios/software instructions. Higher the sensor reported temp, the faster the pwm cycles or the higher the voltage.
I can't claim to have understood all of that, but based on your mention of temperatures, can I assume that the effectiveness of my CPU cooler and GPU fans has a direct effect on how hard a voltage controlled exhaust fan is working at any given time? As in if my heatsink and GPU fans keep their respective components sufficiently cool, the motherboard will "determine" that there is no need for the exhaust fan to spin at a high RPM?
 
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Karadjgne

Titan
Herald
Backwards, sorta. You have 3 independent systems. Cpu is by itself, as are case fans and gpu. The gpu fans speed is determined by the gpu itself (sometimes overridden by software) so when the gpu is under loads, it determines how fast its fan needs to spin. The higher the load, the faster the fans, the more exhaust heat goes into the case. The cpu works the same way. As the cpu gets hotter, the heatsink fan spins faster, determined by the bios settings (sometimes software) for that temp. All cpu exhaust goes into the case.

It's different with case fans, exhaust and intakes. There are several sensors on the mobo. These read the ambient case temps. If the case temps climb, the case fans spin faster. Some mobo's there are no additional sensors, case fans respond to cpu temps.

In a game, if the gpu is at 70°C, the fans might be at 75% speeds, but the exhaust is 70°C put into the case. The cpu might be at 55°C and its exhaust is dumped into the case. The mobo sensors pick up on those temps and increase the speed of the case fans.

The fan headers are linked to a fan curve. Duty cycle according to temp. For analog it's usually starting at 30° x 60%rpm and will go to 70° x 100%. So if case temps are getting to 50°C, then your case fans will be @ 70% roughly. If you have 1000rpm case fans that's 700rpm, if your case fans are 3k industrial Noctuas then you'd be looking at closer to 2100rpm. The bios doesn't care about rpm your fans might be, it just supplies the necessary duty cycle % according to the temp. As temps drop, the % drops so fans slow down, if temps keep rising the % rises and fans spin faster to compensate. At 70°C (default) all cpu/case fans are at 100% duty cycle, it's usually closer to 80°C for gpus.

It's the job of the case fans to supply cooler air and remove excessive heat in a constant flow that allows for better efficiency of cpu/gpu heatsinks. Without adequate airflow your case becomes an oven and those heatsinks become less effective upto ineffective at cooling and pc thermally shuts down. You don't need gale force winds inside, it's better to just have a good, constant flow in/out.
 
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