Positive pressure vs Negative pressure

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zoltar151

zoltar151

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Nov 20, 2013
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i've done some testing in both methods and i'm just looking to get the community opinion on this. i have 212 HYPER EVO cpu cooler with 2 120mm SP120 HIGH PERFORMANCE 2,350 rpm fans in push pull. i have a 69.9 CFM 120mm fan with 3.1 static pressure as an exasut directly behind the cpu cooler. i use the same fan type for 2 exhaust fans on the top. i have a GELID 75 CFM 2.66 static pressure fan as a front intake and a AF120 HIGH PERFORMANCE 62.9 CFM it has low static pressure as a bottom intake.


anyway, i've tried flipping my top fans to make positive pressure and my temps from open hardware monitor were as follows:

THESE READING WERE TAKEN AT 100% cpu load!!!

Positive pressure
Aux: 40c
Sys:54c
Cpu:54-55

Negative Pressure

Aux:41.5
Sys:55
Cpu:55

it's worth mentioning i live in a radiator heated home, on the upper floor. it's summer now so no heat needed but also no vents in the house so food for thought.

none of my other temps changed at all, i decided to go with negative pressure as i have zero dust build up and the whining from the top 2 intake fans due to resistance is just unbearable.



lemme know your fact and views out there i know this thing has been beaten to powder, but gimme your views anyway. this can only help others. :):)
 
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ssddx

ssddx

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May 27, 2009
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generally case positive pressure is considered ideal since negative pressure causes dust to get sucked into all the nooks and crannies of your pc in most houses. it is most noticeable in forced air heated housing, those with pets or animals or if there is a significant dust problem.

however, in terms of cooling performance, there is not much difference.

since you do not appear to have a dust problem (after extensive testing) and since you have other reasons for not wanting positive pressure (fan whine) i would say that negative does seem like it would work for you.
 
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zoltar151

zoltar151

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Nov 20, 2013
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wonderful :). i did have an H80i at one point, so the top exhaust was easier to back up. but by this point i definitely agree. you don't want all intakes nor do you want all exhaust. the pc comes with vents in them to there will always be some type of ventilation. some like to blow air across their components, others like to ventilate the hot air out. many forget that you need a flow system of intake and exhaust in what ever way that is for whom ever. i have found that the vent diagrams for the case you have is usually the best way to go. but again your totally right about the situation depending. i'd like to keep this thread open to see what other views people have out there. i'm not sure how to turn this into a poll thread and have others comment on it but lemme know :)
 
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zoltar151

zoltar151

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Nov 20, 2013
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i will say this about the side panel fan. it DOES make a difference in idle temps but in my experience only by 2c on my gpu as an intake and useless as an exhaust. more food for thought keep the ideas and fact coming people :)
 
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synphul

synphul

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Mar 11, 2011
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No real need for static pressure fans as exhaust, rear or top. Airflow designed fans work just as well since it's not restricted as it is blowing past hdd cages, radiators, cooling fins etc. Too much air difference either way isn't all that beneficial, the idea is to move air through the case efficiently. A case isn't sealed so no pressure/vacuum is created either way. Unless fan orientation/position is causing unusual 'pockets' of uncirculated air, it should perform well so long as the air in the case is being evacuated. Those temp differences are so little they could be purely margin of error.

Dust control may make for a preference one way or the other. Regular cleaning easily takes care of that as well so it shouldn't be an issue.
 
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zoltar151

zoltar151

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Nov 20, 2013
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for sure, i'm only using a static pressure fan aka the sickleflow as an exaust behind the evo 212 because it has a higher cfm rating than the 2 push pull fans on 212 evo. the 212 evo again is using 62 cfm, SP120 high performance pwm fans, they have 3.1 sp. i will be replacing the top fans for bitfenix spectre pro 200mm. i light the illumination and it has 148 cfm which is higher than 2 sickflows. that or ill go with the cooler master mega flow and just take the cfm hit as it makes 110cfm. all this is =/- 10% but i know the sickleflows generate close to 140 cfm on the top.
 
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zoltar151

zoltar151

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Nov 20, 2013
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if i use positive pressure i can feel air blowing out the front panel filters when i use bother sickleflows as intake on the top. using only onoe as intake on the top would still create a positive pressure so it is bad when you feel the air doing this.
 
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