CM 120mm Fan not living up to spec's ?

After reviewing the forum's FAQ (GUIDE: Air-cooling for CPUs, GPUs, and just about everyone of you ) I purchased 2 CoolerMaster 120mm LED fan's (CM Spec's Link) for my new case. I hooked them up and they didn't seem to be pushing thru anywhere near the specified 42.73 CFM as per the spec's...
So I hooked one up to my CM CoolDrive 4 (Fan Controller), and sure enough it was maxing out at 1100~1140RPM (close to the RPM spec's of 1220)...

So to further test this issue, I hooked up a EverCool EC9225M12S 92mm fan (40.9CFM spec's) and placed it next to the CM fan and put my hand behind them both and the Evercool was pushing way more air.

I allways assumed bigger is better, but I could be wrong, why is a 92mm fan out preformaing the 120mm, even thou the 120mm has better Manufactorer spec's?
Why might this be?
I've tested the fan using both the Fan Controller and Conecting it directly to the PSU via a 4-pin Molex.

Please Help,
Thanks,
-BassKozz

The 92mm fan will feel like it is moving more air because the air is much more focused. I own a few of the CM fans and they are within spec.

It hardly feels like it's moving any air at all. Is this normal... is there anyway I can test the CFM ?

youre moving almost the same amount of air through a significantly larger opening. the amount of force the air is going to be pulled out through the 120mm is going to be far less than the 92mm.

the 120mm has more cubic inches than the 92mm, therefore pushing more cubic feet of air per minute than the 92mm fan. because of that it can spin at a lower RPM to push out the same amt of air as the 92mm. therefore the pressure the air is being pushed out is far less than the 92mm.

TSS Modder said:

youre moving almost the same amount of air through a significantly larger opening. the amount of force the air is going to be pulled out through the 120mm is going to be far less than the 92mm.

the 120mm has more cubic inches than the 92mm, therefore pushing more cubic feet of air per minute than the 92mm fan. because of that it can spin at a lower RPM to push out the same amt of air as the 92mm. therefore the pressure the air is being pushed out is far less than the 92mm.

Click to expand...

ok, makes sence...
Which is a better size fan to use to cool HD's? 120mm or 92mm?
Is more "pressure air" better?

I think the 120 is better, it's hits more surface area. and is very quiet.

as for your fan, it is possible the fan could be a defect and not be spinning up enough or could have a deformed fan blade, you should be able to feel some air being pushed.



cooling hard drives don't really take too much, i have one spinning at only 800-900rpm's and it's keeping my raptor cool to the touch. i'd say stay with the 120mm