Which would be better?

[Thor86]

Well?

 

[CheesePoofs]

120mm. Its bigger, so there's more air. Plus 120mm fans are quieter.

 

[Fallen Kell]

Well, not all 120mm fans are quieter, it is only if you have them setup that way But yes, I agree go 120mm if you have the option, why else get the XP-120 if not for using a 120mm fan

 

[Regulator07]

go xp120 with 120mm panaflo, got that on my setup and i have the fan spinning at only 1100 rpm and cpu does not go over 42C full load, if the fan is at max 2500rpm, cpu does not break 40 C, so depending on you case you can lower the fan speed, the xp120 is awesome

 

[cchhrriiss1982]

xp120 with 120mm fan no question. I have it with a 120mm Evercool fan running at 1500rpm and it is nearly silent. Even turning up the rpms doesn't increase cooling, just noise. That is the beauty of 120mm fans over smaller ones, greater airflow means better cooling and lower rpms means quieter.

 

[ribbon13]

Just some info that may or may not be relevant.



At a given CFM (airflow) level, an 80mm fan will be significantly louder than a 120mm fan because of the surface area of the fan. Because the fins on the 120mm fan cover a much larger area, they do not need to turn as fast as the fins on an 80mm fan to supply the same amount of air. Because of this, the noise generated by a 120mm fan, for a given CFM level, will be much less.

HOWEVER, there is a tradeoff.
At a given CFM level, while the 120mm fan will be quieter than the 80mm fan, the 80mm fan will have HIGHER static pressure. In other words, the air that is being pushed from the 80mm fan will be moving faster. This has it's own advantages. For instance, CPU cooling. When choosing a fan to cool a CPU static pressure is important. This is because it's a measure of how fast the air is moving past the fins of the heatsink. In most cases, using a 92mm or 80mm fan of the SAME cfm level as a 120mm fan will give BETTER cooling performance for CPUs.
But that's only for CPUs.

When dealing with case fans we do not care about static pressure generated by the fan only the total amount of air moved. Since 120mm fans can move more air, more quietly than an 80mm fan, these are the fans of choice for pressure insensitive applications.

The quality of the PSU will determine how efficient it is with heat production. Ideally, one 120mm fan should be plenty. But there are so many other factors to consider that vary from situation to situation. Is the PSU near to the CPU? Is the intake on the PSU facing the CPU, thereby drawing more heated air? Where are the heat producing components actually located in the PSU in relation to the fan? How good is the overall case cooling, or is the PSU going to be acting like a needed exhaust for your system?

As to whether a PSU should be considered like a case fan or a CPU fan, I would say more like a case fan. PSUs don't generate nearly as much heat as a CPU, and generally can tolerate much higher temperatures. But, since you are actively cooling components on the inside of the PSU, static pressure does play a part. Just not as big a part as with CPU fans.