Ok so I am using the Cooler Masters Haf 912 Mid tower case and have a question about fans. Currently I am using 2x120MM fans in the front port which I think can support 1x200MM fan. Also I am using 1x120mm fan on the side port which supports 1x140MM fan. My question is it better to use the bigger fans in those ports. Well I am sure the side fan would be better at 140MM but how about the front? Would 1x200MM fan run better then 2x120MM fans? I think my top port also has like a 140 - 200MM fan port as well. But my h60 set up blocks the use of the entire top so currently I can use only the front. 

Let's look at this for a minute. If you had 1 200mm fan on the front that moves 75cfm, compare that to 2 120mm fans with a total area of 240mm. And say those 120mm fans move 50 cfm instead of 75 well you double that 50 cfm and your now pushing 100cfm into the case.
 
Now on the side, if you can only fit 1 fan I'd look for one that has the flow rating and noise level that you want. You may be able to find a 120mm fan that flows 60cfm but it may bet at 40db where you may possibly find a 140mm fan with the same flow rating at 32db because the bigger fan doesn't have to spin as fast for the same air flow.
 
Also I would take into consideration that the majority of fans sold for cooling are 120mm so thats where the most choices are. And the products are better. Alot of the 140mm and 200mm fans are simply 120mm fan motors with bigger fans put on them. So they tend not to last as long.

zophar


Let's look at this for a minute. If you had 1 200mm fan on the front that moves 75cfm, compare that to 2 120mm fans with a total area of 240mm. And say those 120mm fans move 50 cfm instead of 75 well you double that 50 cfm and your now pushing 100cfm into the case.

Now on the side, if you can only fit 1 fan I'd look for one that has the flow rating and noise level that you want. You may be able to find a 120mm fan that flows 60cfm but it may bet at 40db where you may possibly find a 140mm fan with the same flow rating at 32db because the bigger fan doesn't have to spin as fast for the same air flow.

Also I would take into consideration that the majority of fans sold for cooling are 120mm so thats where the most choices are. And the products are better. Alot of the 140mm and 200mm fans are simply 120mm fan motors with bigger fans put on them. So they tend not to last as long.

Thank you zophar. I understand what your saying about the 120mm 50CFM x2 and 1 200mm 75FMx1. So is the only reason people use 200mm+ fans is because thats all they can mount in that spot? Or is it just preference. 
 
I assume this works for exhaust fans as well? 

I have the HAF912 also.  I've had 2x120mm fans on the front before I changed it to 1x200mm.  Reason is because it's quieter.  The larger the diameter, the quieter it is because it runs at a lower RPM.  However it does not necessarily give you the same CFM.  I have front/side intake and top/back exhaust.  

I haven't found a 200mm or larger fan that isn't crap.  Stick with two 120mm fans in the front.  A decent pair of 120mm front fans will not even have a noticeable noise increase over a 700 RPM/19 DBA Cooler Master 200mm/230mm fan, and I say this with experience.  
 
As for the side fan, there aren't many good 140mm fans at all.  The Silverstone AP141 is probably the highest quality practical one (that is, 25mm thickness and no absurd RPM) and it is quite costly.  This particular one also has a poor CFM/noise ratio due to the integrated fan grill, which is very restrictive but aids in directing the air straightforward (something not needed on a side fan).  So in the end my recommendations are; 2x 120mm front fans, 1x 120mm side fan.

Yah I am honestly not to worried about the noise. I am more concerned with air flow. 

You can get jet-engine fans then, they're loud but pushes air like no other.

Xtrem


You can get jet-engine fans then, they're loud but pushes air like no other.

 
Ehhhh I am not worried much about noise but I do not think my family would be happy with me having jet engine fans. Plus I am sure they are pretty expensive.