The air cooling scheme must be adaptable to the particular case and in this case some of the general assumptions won't apply here. A single rear exhaust fan pushing thru large open grille is moving orders of magnitude more air than thru the tiny holes on the top of the case.
1. We have two forces acting here ... The major one is that air or liquid moving in an open system will follow the path of least resistance. Test:
a) Take a soda straw and see how much air you can blow thru it and how hard you gotta blow to make that happen. You'll notice that straw fits thru the rear case grille.
b) Now take a 5 swizzle sticks, typically used in mixed cocktails and blow air thru that. You'll notice that it's opening is comparable to the openings on the top vent
Which is easier ? Now let's look at that top vent and what do we see under it ? It's an air intake filter which adds more resistance.
2. Of course, we all learned in 8th grade earth science that hot air rises. But we also sat in grandmas kitchen with that ceiling fan and the air was definitely not rising.... it kept blowing my napkin off the table. Hot air rising never did that.
25C air has a specific weight of 8.166 lbs / cuft
30C air has a specific weight of 8.104
That's 0.075% lighter ... which means it's a miniscule force pushing upwards. So just like grandmas kitchen, when that fan is spinning it's not going to be a battle, the fan wins. So while I'd say yes, take advantage of that teeny uplift force if you can, the impact of forcing air thu the tinier holes is far greater. If ya wanna test it ?
a) use a fog machine... leave just the intake fans on and see where more air comes out ... the big giant holes on the rear of the case or the tiny pencil point holes on the top of the Enthoo Pro
b) Lay a napkin on top of the case with before installing the top fans off and see what happens... it barely moves. Now hang it over the rear of the case, it flops in the breeze.
So with just intake fans operating, we have a battle between "hot air rising" and "air following the path of least resistance", ... and the 2nd one wins, handily.
3. The issue I have seen with the Pro with "adding 1 intake and + 2 exhaust is that intake fans are limited by intake dust filters which, even when clean, can cut as much as 1/3 of the air flow. With 3 in and 2 out, you can have pretty much even flow; when adding 2 + 1 (now 3 exhaust + 2 intake), you definitely should expect negative case pressure.
On the other hand .... exhaust fans on the top are not very effective pushing thru the small holed grille and inlet filter. Imagine affixing a piece of pegboard on the exhaust side a 24 x 24 window fan ... while on the intake side, there is also a considerable reduction, we have a lot of air trying to fit thru little tiny holes resulting in a lot of "blow back". You will usually notice that exhaust fan grilles usually have larger openings.
Lets not forget you also have the GPU also pushing some air out so you wind up sucking air in thru the rear case grille .... and what's coming in with it ? 1) hot air exhausted by the GFX card and PSU and 2) dust. This is immediately evident with fog machine testing... having the fog exhaust at the rear of the case, it takes just seconds before you see clouds inside your case. I have tested it with the Enthoo Pro, Enthoo Luxe and Enthoo Primo when using top exhaust
4. If you read the installation instructions on say a H100i, it is very clearly stated that "for best performance, fans shall should be intakes". This is consistent with what every custom loop does. Phanteks figures most folks will follow long established WC wisdom and CLC manufacturers written instructions so that's why there's an air filter. If I was designing those for air exhaust I'd use this:
http://mnpctech.com/case-mods-gaming-pc-liquid-modding-custom-computer-mnpctech-overclock-cooling-fan-grills/modders-mesh-honeycomb.html
After adding 3 fans, we'd have (2) 140 mm intakes and (2) 140mm exhausts
Front: 1 x 200m (included)
Top: 3 x 140mm ... (2) new exhausts go here **
Rear: 1 x 140mm (included)
Bottom: 1 x 140mm .... (1) new intake goes here
** If you want to remove the air **intake** filter that is mounted in the top of the case ... requires unbending and re-benbing steel tabs so don't wanna do it often
We now have 3 exhausts and 2 intakes ... and tho 1 intake is bigger (+33% cfm), it also spins a lot slower and has lower SP.
Intake = (100% + 100% + 133%) x 75% due to filter restriction = 175%
Exhaust = (100% + 100%) = 200%
Again, fog testing that air is being sucked in thru case grilles in this condition.
From a cooling perspective, it doesn't matter whether a fan is going in or out... it's all about air turnover. If you have 5 fans moving 50 cfm (250 cfm) you how many times is will the air in this case turn over ?
21.06" x 9.25" x 21.65" = 2.4 cu.ft. say (85% empty space) ~ 2.1 cuft
With 250 cfm being pushed thru it ... that's 119 air changes per minute or 2 per second. When the entire case contents being turned over twice every second, the amount of air that would be gained / lost taking advantage of hot air rising is insignificant....0.075% change would be 119.08 versus 118.92
Your car engine gets cooled by taking air in thru the front and exhausting it out the bottom, they don't think much about hot air rising as the cover it with a solid hood. And what about the radiator ? Do the use fresh cooler outside air as intake in and exhaust hot air right on the engine ... or do they take the engine hot air and blow it out thru thru the radiator ?
Whether a fan is intake or exhaust really depends on where it is....
a) Bottom .. always in
b) Front ... always in
c) Sides ... always in
d) Back ... always out
e) Top ... while out is the automatic "logical* answer, it simply doesn't work here w/ the Pro and that's why Phanteks gives you an air intake filter. The case simply isn't suited for it.
-You can't have 3 out and 2 in without sucking most of hot air exhaust from PSU and GPU right back into the case.
-The top has an air **inlet** filter for a reason
-When you build positive pressure within the case air just doesn't leave thru the tiny top openings ... instead it follows the path of least resistance and exits thru the large grille in the rear
On other builds like the 500R ..... the way this case is designed, top exhaust is an automatic
Front: (x2) 120mm intake
Top: (x2) 120/140mm exhaust
Rear: (x1) 120/140mm exhaust
Bottom: (x1) 120/140mm intake
Side: (x2) 120/140mm intake
5 intakes - (2) front (2) side (1) Bottom
3 exhaust - (2) top (1) rear
In the Pro, and gain we don't know what's in here.... I'd use
Front: 1 x 200m (included)
Top: 3 x 140mm ... empty, anything her can exhaust via "hot air rises
Rear: 1 x 140mm (included)
Bottom: 1 x 140mm .... (1) new intake goes here
That (100 + 100 + 135) should more than cover the heat generated by CPU, MoBo and say a AIB 1070 at stock settings
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