40 cfm fan for Exhaust? is it good

[NeonShadow]

im wondering if 40 cfm is still good as an exhaust... i only have 1 120mm exhaust(rear) and it has 71 Cfm but looks ugly.. i want to buy 3x120mm rgb fans but it has 40cfm so im thinking since i'll have 3 exhaust 1 rear 2 at the top.. then 40 cfm is good right? i have 2x140mm intake in the front 93 cfm... is this a negative or positive airflow?

 

[HEXiT]

that would be a negative air flow.
you have the 3 120's pulling out the case (+ 1x140mm out depending on your psu orientation.) but only 2 in., that would make your case a negative pressure environment. basically turning your case into a dust magnet as dust will climb in to the case through every seam and vent.

if you want to stick with the x3 120's@40cfm then get x2 70+cfm front fans..
this will turn your case into a positive pressure environment for the most part and only when the psu fan kicks in would it become a negative environment, but to a much lesser degree than your previous setup.

with this setup you should in theory have an optimum air flow setup. positive pressure at idle. and negative at load.
you get the benefits of both setups.
minimised dust due to positive pressure at idle.
and the better heat dissipation of a slightly negative pressure case at load

 

[Mikel_4]

Rear exhaust fan was meant to suck warm air generated by CPU air cooler + GPU open air cooler such as ACX or Windforce, the most important stuff in positive air pressure is moving air (rated in cubic per minute) reach, you can do simple test to see if your case is at suffice air flow.
Intake
Grab a thumb size cotton, place it in front of intake fan, run PC, the intake fan should fly the cotton all the way to rear, this should give you the idea of warm air from graphic card accumulate.
Exhaust
Place cotton on back side of graphic card, see how your top exhaust fan perform.

 

[NeonShadow]

that would be a negative air flow.
you have the 3 120's pulling out the case (+ 1x140mm out depending on your psu orientation.) but only 2 in., that would make your case a negative pressure environment. basically turning your case into a dust magnet as dust will climb in to the case through every seam and vent.

if you want to stick with the x3 120's@40cfm then get x2 70+cfm front fans..
this will turn your case into a positive pressure environment for the most part and only when the psu fan kicks in would it become a negative environment, but to a much lesser degree than your previous setup.

with this setup you should in theory have an optimum air flow setup. positive pressure at idle. and negative at load.
you get the benefits of both setups.
minimised dust due to positive pressure at idle.
and the better heat dissipation of a slightly negative pressure case at load

i think you misread my post.. i said i have TWO 140mm fans in front as an intake and both of them has 93CFM so my point in this post is actually being said that i have TWO 140mm fans with a very high CFM if i were to buy THREE 120mm but 40cfm as an exhaust.. will it be an optimal airflow? will it be positive or negative flow?

 

[HEXiT]

186/2cfm =93
120/3cfm =40

186-120= 66cfm
psu? - 66 cfm =

if your psu is externally fed then you could turn the front fans down to balance out the 66cfm deficit

 

[NeonShadow]

186/2cfm =93
120/3cfm =40

186-120= 66cfm
psu? - 66 cfm =

if your psu is externally fed then you could turn the front fans down to balance out the 66cfm deficit

my case has a psu shroud and its facing down so im not really concerned about it