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Negative vs Positive pressure

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#1
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#2
positive air pressure = more intake power than exhaust
negative air pressure = more exhaust power than intake

its not a huge deal either way, honestly you're looking at most at a 5c difference, if that. well within margins of error and varying ambient temps.

though if you plan to go positive, make sure you have filters at every intake slot or else you'll just be ending up with more dust.

also you'll hear a lot of "hot air rises" being thrown around but trust me, it's already been debunked and not true in a forced air path situation.
 
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#3
I'm on the process of properly cooling my case and this topic has come up for me. I was reading about positive vs negative air pressure and wanted you guys opinions. Read a good thread at tom's hardware: http://www.tomshardware.com/forum/238184-31-case-airflow-positive-negative-pressure
Not sure which way to go
My two cents; this is a stupid debate.

A fan is rated to move a certain volume of air, at a given temperature and density, over a certain period of time. The temperature and density are rarely defined, and flow interference is never really touched on. As air is extremely compressible, neither of these options actually makes much sense.


Thought experiment time. You have a case with no outlet, and one or more inlets; what exactly have you made? They call this a compressor. It takes air of known temperature and density, but then jacks both of them up to fit more molecules into the containment vessel.

Likewise, you could have everything flowing out of the case. This is a vacuum tube. Energy transfer here sucks (you lose conductive heating), but the vacuum is a superb thermal energy transfer barrier. This is how some long lasting food products and beverage containers prevent heating.

So, the take away here is to have approximately even input and output. The air will tend to flow, rather than compress. People argue that less dust is collected in positive pressure configurations, but there is no real evidence out there, beyond anecdotes.
 
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#4
I'm thinking in my case with 3 120mm's on the bottom and some on the side, positive is the way too go. Both theories make sense thou
 
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#5
So you recommend whatever works best
 

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#6
There is one thing worth noting. If you have filters on your case and you expect them to be effective, if you have more exhaust power than intake power, you're going to pull in air (and dust) from every hole in the case and as the filters fill up with dust, it will only get worse and worse. I personally prefer filters full of dust as opposed to heat sinks, so it's worth a consideration from a cleaning perspective. I don't like having to clean out the entire case when I can just clean out 4 filters instead.
 
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#7
So you recommend whatever works best
...

My recommendation is to think of the air as a particle flow, not as some static system. The air has to have a definitive path, minimal obstructions, and there has to be reasonable orientation. Pull air from the bottom of the case, and output it either upwards or backward.

In regards to what works, I'd pull air in with the three on the underside. I'd mount the two side fans to output air. I'd leave the back of the case open, but make sure that the power supply exhausted air out the back. If the CPU cooler was oriented such that the air flow direction matched the output on the side of the case, you'd be able to direct flow inside the case.

This is all predicated on using the case in your system specifications. I don't have any experience with the case, so please take any advice I give with a grain of salt.
 
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#8
Honestly speaking. I don't give a damn. I just ensure that my case doesn't have a random hole from where air is leaking out.
 
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#9
Ive found positive case pressure works well when I have had a large cpu cooler with an anemic fan on it, for example my old Coolermaster V8.

Usually temps seem to be the best when I put a ton of fans on every spot possible. I tried blocking a few fan holes on the Antec 300 case to see if it improved air throughput but temperatures were much better with every fan hole being used (except the dumb back side of the motherboard hole). Graphics cards especially like direct airflow, if you add a side panel fan, it will help a lot.
 
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#10
i think its just taste since both of them flow the same air, but many cases maker use positive air (many intake fans)
but i like positive air since the air flow may straight to your hardware than negative air. but any that you do dony forget use air filter to minimize the dust
 
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#11
I like my parts to stay clean and the case to look clean. Positive pressure with filters achieves this. The downside is the cooling is not as efficient. This is a fact
I have 6 fans going in one out
 
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#12
I like my parts to stay clean and the case to look clean. Positive pressure with filters achieves this. The downside is the cooling is not as efficient. This is a fact
I have 6 fans going in one out
sometimes too much fans is not good = giving you much noise, but for some people its ok
and each rig may need different setup, like SLI/crossfire need more airflow for their cards
 
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#13
sometimes too much fans is not good = giving you much noise, but for some people its ok
and each rig may need different setup, like SLI/crossfire need more airflow for their cards
They are all turned down. Its not very loud at all. I actually could take a few out not that Im not running crossfire
 

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#14
I'm thinking in my case with 3 120mm's on the bottom and some on the side, positive is the way too go. Both theories make sense thou
I wouldnt put in fans on your side panels, they tend to disrupt the air flow going from front to back/top.
 

ogharaei

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#15
Positive air pressure won't let as much dust settle inside your case.
 
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#16
I have 4 fans pushing air through 240mm and 280mm radiators. That's all. 0 fans sucking air into the case. I assure you that this is the best way to make your pc look like a dust hoover as there is no easy way to force dust to go through filters.
 
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#17
Always looked for positive pressure, it keeps the cat fur out.
Also if you've a strong negative pressure it can lead to cooling issues with the PSU as its fan struggles against the natural inwards airflow created by negative pressure.
 
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#18
I wouldnt put in fans on your side panels, they tend to disrupt the air flow going from front to back/top.
That's kinda what I was thinking
 
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#19
To me it's more about creating an airflow that allows critical components to be properly ventilated with cool air and hot air to be exhausted out of the case, the ATX spec is really good at this, suck cool air from the front and bottom of the case and arrange all the fans in the back and top of the case so they exhaust the hot air that will accumulate in these areas by convection, all of my builds follow this principle and I hardly have issues with overheating in any of them.
 
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#20
^ this.
i usually let fans to take cool air to help the active cooling system like radiator and my blower-type GPU to get cool air instead of heated air from within the case.
my setup is heavily unbalanced with 2 low speed fans and 2 medium speed fans as intake and only 1 low speed fan as exhaust in the back but i never experienced overheating except cooling this haswell is such a pita without delidding :slap:
 
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#21
So I added my three tricool fans to the bottom today and have them on the high setting. The noise they make doesn't bother, but better yet, they are working great. I OCed my cpu back to 4.4 and it's holding stable. I have my GPU at 1300/1650 and it's holding stable. Made a world of difference. I want to get a AIO cooler for my card now to see if I can pull off 14, 15 or maybe 1600 @ core.
 

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#22
So I added my three tricool fans to the bottom today and have them on the high setting. The noise they make doesn't bother, but better yet, they are working great. I OCed my cpu back to 4.4 and it's holding stable. I have my GPU at 1300/1650 and it's holding stable. Made a world of difference. I want to get a AIO cooler for my card now to see if I can pull off 14, 15 or maybe 1600 @ core.
Youll need ln2 to do anything over 1400mhz usually, though custom water cooling could get you maybe near 1500.