Fan ratio's and CFM?

Ok, I am pretty sure I want the cm 692 case and I have been picking out the fans for them.
Obiviously the 692 has plenty of intake which out dues even the HAF series. What isn't so hot is that
the exhaust is two top fans and a rear, and here is my question.

The 692 allows me to either get 2x 140 or 2x 120mm, and I can't find any 140mm fan thats over 80cfm, but the fans I
want the CM RED LED 120mm 90CFM @ 2000rpm doesn't come in a 140mm size.
So does 2x 140mm at less cfm's do better exhausting than 2x 120mm's running at 90cfm, about double the cfms??

I thought about it, and I even considered the slipstream from scythe cause they were running at 110cfm, and at that
rate I would even top off the HAF-X as far as top exhaust.

In my head even at 40-50cfm's the 140 are 2cm's wider all around so they can take more air at one time, rather than
the 120mm sucking the air like a funnel. I almost think it would be an even match but the 140's aren't shiz without
any air suction.
5 answers Last reply
More about ratio
  1. I think what you're missing is that cfm is a measure of volume.

    Fan 1 is rated at 50 cfm
    Fan 2 is rated at 100 cfm

    Whether Fan 1 is 80mm or 240mm, it will never push more air than Fan 2.

    50 cfm is how much air Fan 1 can exhaust or intake. The end.

    The only numbers that truly matter for fans is cfm and db (if you care about the noise level). Size just limits where they'll fit (though it does factor into what the final cfm rating is).
  2. Personally i prefer quiet fans so i'm more interested in the decibel rating.
    Cfm's don't concern me too much.
    As you probably already know these are the 140mm CM fans for the 690 series no red led
  3. So if I get this correctly, it doesn't matter if I had 2x 200mm or 2x 120mm if they were both rated at 110cfm,ok.
    I don't care about noise, thats what fan controllers are for, there for people who want to get hardcore air flow at loud
    noises but use the controller to adjust when idoling, so cheap people like

    Anyways, so I guess the only thing I would like in the cm 690-2 is a psu cover like in the HAF-X, which I know I can rig something up. I have considered just using two pieces of thin wood and making a L shape, so an identical piece like in the HAF-X.

    I have enough money for the HAF-X, I just think it is kinda hugemongus, and probably not for me, cause I don't plan on
    3-4 gpus. I liked the HAF-X cause of all the big fans but after your explamation I can get a 690-2 freezing.

    So 690-2 w/side panel + all fan slots= 190ish give or take and the HAF-X and 1 200mm fan its around 250(cause of shipping its an extra 25)
    So i could either save money, or get a fan controller and spend the same amount as what I would!!!!

    I was wondering if exhaust and intake cfm's should match up? like if I had 480cfm total intake, but only like 300cfm exhaust, should I make that a lot more even?? Or does it matter?
  4. Ideally, you have more intake than exhaust. This should provide positive pressure, which will help to keep the case a little more clean. The amount that intake is greater than exhaust shouldn't matter too much, unless you notice heat starting to get out of control.
  5. Well my plan is to take the top 140mm that comes with it and put it in the front, cause the theme is red.
    Then I am going to put two red cm 120mm up top, two on the hyper 212+, and two on bottom.
    Then the fan that comes with the 212+ I am going to rig it either to the two holes left on the top part of the harddrive cage.
    and if not, I will postion the taken out side HD cage and use it some how.

    Then I am going to get the side panel for the case, so I will get an additional 120mm red.
    Then two 80mm's one for the bracket and one for behind the mobo.

    and finally I am going to use the stock rear fan, and possibly upgrade later. Cause the red led from cm is better than
    there average fans, because it tops out at 90cfm at 2000rpm's.
    Plus the fan is pretty quiet, its like 26db at 90cfm if I remember right.

    I added up all the cfm, and the 692 would tear the HAF-X apart, only because you can fit more fans in the same amount of space, that are pretty much equal cfm.
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