The general wisdom is, all things being equal, you want more intake than exhaust .... the general wisdom goes out the window if the fan mounting for the inlets are not filtered. The 450D series is a bit unbalanced in this respect as it has (4) exhaust locations and only 3 intake locations. You don't really need any exhaust fans, most water cooling build have very few.
It's oft thought that because you have air blowing in, you need to have fans blowing out. This has no basis in engineering or thermodynamics. Evert cfm that is blown into your case will find it's way out.... if it didn't, the case would explode.
Think about your home, your office, your school..... most buildings are ventilated by exhaust fans, and use open grilles or louvers to provide make up air. You have an attic fan that pulls air out of your house near the ceiling ? Does it have a companion fan blowing air in ? The use of intake and exhaust fans is dictated by the form factor of the PC. Ideal design would be either:
- Double row of fans across top sucking air out and fresh air coming on thru grilles at bottom
- Double row of fans at bottom blowing air in and open grilles at top letting air out
We don't have that cause the form factor of most PCs has other stuff occupying that real estate.
You have (Bold installed):
[]Fan Mount Locations[/u]
Front:
(x2) 140mm
Top: (x2) 140mm
Rear:
(x1) 120mm
Bottom: (x2) 120mm
If just adding one, I'd add a 140mm to the top giving you (2) x 140mm in versus (1) x 140 + (1) x 120 out. Of course if the bottom is not filtered, it's not gonna make a whole lotta difference anyway
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Has 3C cooling advantage over Noctua AF-15
Filling the case with all possible fans would leave negative case pressure which will suck air in thru grilles and that would take dist with it..... but again, if the intakes at the bottom are not filtered, it becomes a moot point as you'll get way more dust being blown in than sucked in.