The most commonly given negative effect of negative air pressure. Speaking generically ... the much greater concern is the temperature of the air carrying it in. The factors here are:
1. Case Placement - Is your PC installed in a desk 'cubby', under your desk ? In a corner of a desk in a room corner ? .... On a desk against a wall ? ... is there a baseboard heater behind your desk ? Are their ceiling or other fans within the room ? Your PC case is really just a small version of your room ... just as air temps vary by location with in a case, the vary within a room. Given the typical case placement in one or more of the conditions described above, the air in this area is normally subject to little changeover because of the semi enclosed position of the air space.
2. Heat Recycling - Looking at your link, if a negative pressure situation arises, the path of least resistance for that intake air deficit will be the large open areas on the rear grille and vented slot covers. With little air movement, let's examine any hear sources in this space:
a) is the a baseboard heater on the wall under the rear of the case ?
b) Is your PSU exhausting it's heat at the rear of the case ?
c) Is your GPU(s) exhausting air into that space ?
Do you want the source of your cooling air to be *preheated* by any of those things ?
3. Intake and exhaust fans are created equal but don't function that way. Let's say that your (6) fan mounts have identical fands and are utilized as (3) imtake and (3) exhaust. Do you have balanced air flow ? Your intake air will be impacted by the inlet air filters. Clean they can restrict air 10-15% ... clogged with dust, they can go to 30% or more. Let's pick 20%. And each fan = 1 Equivalent Fan (EF)
3 Exhausts x 100% air flow =3.00 EF
3 Intakes x 80% air flow = 2.40 EF
So you have the equivalent of 0.60 fans coming inn that rear grille / slot covers....
Other factors affect fan placement ... some of these may contradict the others.
4. Water Cooling - i can not understand the logic of having rad fans as exhaust ... back in the day, there were 2 rules of water cooling :
Rule No. 1 - Never mix metals in a water cooling loop... 95% of AIOs break this rule.
Rule No 2 - Rad fans always blow in, no exceptions ... 95% of AIO users break this rule
a) Yes we all learned in 8th grade earth science that hot air rises ... The effect is minimal and there's no giant fan in the sky like we have in a PC case.
b) This is simple thermodynamics. What is cooler ... ambient air or interior case air ? The amount of cooling provided is proportional to Delta T.
Ambient air = 23C / Case Air = 28C / Coolant = 33C
Intake Air Cooling Delta T = 33 - 23 = 10C
Interior Air Cooling Delta T = 28 - 23 = 5C
At these temps, using ambient air is twice as effective ... and since interior case air is always warmer than autise air, blowing in will always be more effective
If you want the coolest CPU temps, you M U S T use the coolest available air source ... thermodynamics ... it's called a law for a reason. And that's why AIO manufacturers tell their customers to install this way.
Unfortunately, with only a rear mount available for a 120mm AIO you are essentially limited to a air exhaust situation.
5. Mounting location - As hinted above, regardless of the above... fan mount locations will most often be the primary determinator of how the fan will be used.
Rear - Here, you will almost always have to do exhaust ... even if it's an AIO.
Front - Again, these are the locations most often equipped with flters and with a open source of air from an unenclosed space, it will almost always be intake.
Bottom - As above
Side - Can go other way subject to location, having an air intake blowing air between XF'd or SLI'd GFX card always helped eliminate the up to 10C difference in temps between top and bottom cards.
Top - Here's the big tossup.... if there's a radiator up there, then the decision is made. The deciding factor here will be the air balance .... If you can have these fans blow out and still maintain positive air pressure with a bit of dust on the filters, you can install this way. If you can't. you are not "getting the heat out of the case" , you are recycling it.
6. Getting the heat out of the case - few people consider the effect of the open grilles on cooling the system. Have a attic fan in your house ? Ever work in a restaurant kitchen ? Did the buildings ever collapse ? They do not collapse because there are available intake sources. In order to remove heat from an enclosed space one needs both an intake air inlet and exhaust air outlet. The air mover can be at either location with no impact. Take a bedroom ... after a hot day, one can place a fan in a window to cool the room down. What happens when you ....
a) place and exhaust fan in a window .... nothing
b) place and intake fan in a window .... nothing
c ) place and exhaust fan in a window and open another window .... the fan will move XY cfm of hot air into the room and replace it with XY cfm cool outside air
d) place and intake fan in a window and open another window .... the fan will move XY cfm of cool outside air into the room and push the hot inside air out of the room
The impact on the room air is temp is the same ... exactly the same
The same thing inside the PC ....
When we put intake fans on the top of the case with a radiator, it pulls in cooler ambient air into the case and push the hot exhaust from the rad and all the heat radiated from the other components out of the case thru the rear case grille. When you put exhaust fans on the top of the case with a radiator, you can't cool the CPU as well as you are using warmer air and you are sucking in air preheated by PSU and GFX card exhaust.
If we are worried about the radiator exhaust impacting other components ... the exhaust heated by the 75 - 120 watts from the typical CPU ? But not worried about the impact on other componenets preheated by 650 watt PSU aor up to 250 watt GFX card ? It must be recognized that a typical mid tower with 6 fans will turn over the entire case air 1.5 - 2 times a second ... The air coming out of a radiator is at worst gong to be 2-3C above ambient ... What component is going to be negatively affected by that temp ? When you exhaust the AIO, you are preheating the air that cools the 75 - 120 watt CPU with about most of the heat from your 250 watt GFX card that was exhausted into the case, but you are also sucking any that went out thru the exterior vent back into the case. You have a small amount of heat from the rad being pushed out of the case by the radiator intake fans thru the rear grill at least 1.5 times a second ... there is no heat buildup.
If you has a 240 / 280mm on the top I would ask .... do you want to use air preheated by your 165 watt GFX card a, 30 watt MoBo, and 20 watts of miscelleaneous compoinents ?
So where do you do from here ?
Front: 3 x 120 or 3 x 140 mm
Top: 2 x 120 mm or 2 x 140 mm
Rear: 1 x 120 mm
If you keep the existing AIO, if using all 120s, I'd expect that youd have a bit worse than the 3.00 EF Exhast / 2.40 EF coming in situation as the AIO likely has an extreme speed fan which will push more air than the others. I would:
Use (3) 140s in the front as intakes ... They should push about 20% more air than 120s of the same model and rpm (3 x 0.80 x 1.20 = 2.88 EF)
The rear AIO as exhaust ...
The top I would leave empty. You don't have large heat load (@ 280 watts) ... The (3) intakes will definitely mainttain enough positive case pressue to force air thru both the rear and top grilles.
but I like the coolness of the blue over an overpowering red or flashing rainbow coloured rgb
