Case-fans, confused about CFM.

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pigstriker

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So my rear 120mm fan broke and I need a new one, but I've never had to shop for a fan before so it's a little confusing. Based on what I've read so far, I need a high airflow fan, but I'm really confused about the CFM units. I read on a reddit thread that Nocuta S12 and Corsair AF120/140 are good high airflow fans, but why are their CFM's so low? If they're supposed to be one of the best high airflow fans, how come there are cheaper fans with higher CFM's? Does high CFM not necessarily mean high air flow?


Here's my case: http://imgur.com/NQ56MXe
 
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synphul
It depends on your budget which will somewhat narrow your choices potentially. From there it depends on your case and what size fans you can fit there, is it 120mm only, is 140mm an option etc. Cfm (cubic feet of air per minute) is a measurement usually taken in free/open air tests meaning no restrictions like fan grills or filters.

Noise is a consideration, some fans move similar air at lower db than others. Some have the same db (sound pressure level) but in different tones, high pitched noises can seem louder than lower pitched tones so seem quieter. A whistle at 30dba is going to be more intrusive usually than bass at 30dba.

Some fans have better more reliable bearings than others, cheap fans tend to use cheap bearings that...
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madmatt30

madmatt30

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The 2 fans models you mention strike a good balance between airflow, speed & noise.

Yes you can get cheaper fans with higher airflow that run at 2000rpm but you will pay for that in respect to decibel noise level.

The AF 120 is a great fan for exhaust use & reasonably priced.

Also on a budget level consider the arctic cooling f12 series
 
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pigstriker

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Is this true? Do I really not need to overspend if it's just an exhaust fan?
 
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synphul

synphul

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It depends on your budget which will somewhat narrow your choices potentially. From there it depends on your case and what size fans you can fit there, is it 120mm only, is 140mm an option etc. Cfm (cubic feet of air per minute) is a measurement usually taken in free/open air tests meaning no restrictions like fan grills or filters.

Noise is a consideration, some fans move similar air at lower db than others. Some have the same db (sound pressure level) but in different tones, high pitched noises can seem louder than lower pitched tones so seem quieter. A whistle at 30dba is going to be more intrusive usually than bass at 30dba.

Some fans have better more reliable bearings than others, cheap fans tend to use cheap bearings that either causes the fan to slow down or wobble, wears out, can create grinding noises in a relatively short period of time compared to nicer bearings.

High cfm fans with low static pressure (think 'muscle' when moving air) can bog down in a hurry vs a fan with higher static pressure. A rear exhaust fan is one of the least restrictive fan positions on a pc case but cases all have fan grills on the back to prevent sticking fingers in the blades. A fan rated at 60cfm may only blow around 50-55cfm out the back of a pc case because there's 'some' restriction there.

If all you're looking for is a cheap exhaust fan, single speed, maybe something like one of these.
http://pcpartpicker.com/product/sdZQzy/cooler-master-case-fan-r4l2r20acgp

If you want one that's pwm (variable speed 4pin) maybe one of these.
http://pcpartpicker.com/product/DPZQzy/cooler-master-case-fan-r4bmbs20pkr0
http://pcpartpicker.com/product/KzQypg/arctic-cooling-case-fan-afaco120pcgba01

All of those are around $10 or less.
 
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