Question about intake and exhaust fans

[Luis Felipe Rodrigues]

Hello, currently I have a Corsair H80i (which has 2 fans, one in each side of the radiator) and 1 other fan as exhausts, plus 3 intake fans (1 on the front, 2 on the side), and I'm about to buy new fans because the old ones are getting too loud. I put 3 intake fans initially because the H80i has 2 fans and I counted it as 2 exhausts (even though both use the same "exit"), making it 3 exhaust fans total, so I added 3 intake fans to have the same amount of intake and exhaust fans. The new fans I'm gonna get are Noctua NF-S12A FLX, I want this model because it's silent, but since they're expensive I'd like to know, is it really necessary to have 3 intake fans with the H80i + another exhaust fan setup? Because if having only 2 intakes is enough, I'll only have to buy 3 fans instead of 4, and that would make a big difference since Noctuas are very expensive in my country (I live in Brazil), but at the same time my country is very hot and I'm not sure if lowering the amount of intake fans is a good idea. Any help is appreciated.

 

[raisonjohn]

Count the 2 radiator fans as 1 fan only. Fans in a series (like that in your H80i) will produce the same amount of airflow (but increase in static pressure); fans side-by-side will produce more airflow (but same static pressure).

Also, it's not the number of fans that determines if you have a balanced/positive/negative airflow, it's the fan design itself and how much CFM (airflow) can it intake/exhaust given a certain RPM (speed).

 

[Luis Felipe Rodrigues]

Thanks for the explanation, I didn't know about the side by side vs series thing. I still don't know if I should have 2 or 3 intakes though, which do you think is better? The Noctua fans I'm gonna buy have 63,27 CFM at 1200 RPM, and I use the H80i in quiet mode, which makes both fans spin at around 1300 RPM, not sure about the CFM on it though.

 

[raisonjohn]

It's really a case-to-case basis as there are a lot of variables in determining the sweet-spot for the number of fans to be installed in a given chassis (and given environment).

More often than not, a 2x intake + 2x exhaust is enough and adding any fans to that will most likely result in very minimal change in temperature. Of course, the advantage of adding more fans is to lower the noise levels by producing the same amount of airflow at a much slower rpm.

Since you are on a tight budget, I suggest you just get 2 Noctua's for your intakes and observe the temps. Try to play around with the other fans you have and see if adding another intake would have dramatic effects on your temps.

Here's a nice test video using different fan quantities/configurations in a typical PC case (although this is using an air CPU cooler) and their corresponding temperature readings: https://www.youtube.com/watch?v=8OmkmluAYAQ

0 Case Fans (Air Cooler Only) = CPU: 71C | GPU: 92C
1 Rear (Exhaust) Fan = CPU: 64C | GPU: 85C
1 Top (Exhaust) Fan = CPU: 65C | GPU: 83C
1 Front (Intake) Fan = CPU: 67C | GPU: 80C
1 Front (Intake) Fan + 1 Rear (Exhaust) Fan = CPU: 60C | GPU: 79C
2 Front (Intake) Fans + 1 Rear (Exhaust) Fan = CPU: 58C | GPU: 77C
2 Front (Intake) Fans + 1 Rear (Exhaust) Fan + 1 Top (Exhaust) Fan = CPU: 55C | GPU: 76C
2 Front (Intake) Fans + 1 Rear (Exhaust) Fan + 2 Top (Exhaust) Fans = CPU: 55C | GPU: 76C <-- Adding 1 top fan = no effect as above

 

[Luis Felipe Rodrigues]

Thanks, I think I'll put 2 intakes for now then.