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Positive or negative pressure in your case?

XZeroII

XZeroII

Lifer
Would it be better to have a positive or negative pressure in your case to achive maximum cooling? As an example, 2 fans pulling air in and 1 fan pushing air out? or 1 fan pushing air in and 2 fans pushing air out? Or maybe try to have even pressure? What do you think?
 
Even pressure is the best, but hard to achieve. For the best case cooling, negative pressure is better than positive, in other words, more air blowing out than in.
 
I agree, slightly negative or even pressure would be the best... positive pressure is useless, since the hot exhaust air has nowhere to go
 
Really depends on how much air you are pushing through the case to begin with. I mean if you are pushing 200CFM through the case per minute with a slight positive air pressure it would not matter. So comments like "positive pressure is useless, since the hot exhaust air has nowhere to go" entirely depend on the established flow rate through your case.

I push a lot of air through my case and prefer a slight positive pressure. It keeps the dust out and all the air entering my case is then filtered. Whereas a negative pressure would end up pulling dust through your drives (ie. burner, cd-rom, zip, floppy etc.).
 
What you don't want to do is over power PSU fan and pull hot air in throught the PSU ...

But Try to get even flow ..

Get a good case like the Antecs with 4 fan holes two in front and two Out hole in back ..

You dont want to pull hot air coming out of PSU back into box ..

In Front / Out Back
 
Have to add my $.02 here... I prefer more intake than exhaust. A slight positive pressure is not a bad thing, as it keeps the system from drawing air in through other openings in the case, like drive bays etc... Along with that air you get dust. Dust sucked through your CD ROM or floppy drive is not really a good thing. I much prefer to over intake through a filtered fan, and keep things a bit cleaner.
 
Mine is about as even as I can get it. I enlarged the front intakes to help airflow, and I have a Panaflo L1A 80mm in my PS blowing and the same in the front, sucking. 🙂
 
2 Cool,
I have to agree I do have postive pressure on mine 🙂
3x 80mm and a 92mm in and 2x 80 and PSU out ..

I guess I am not even hehehe
 
1 68cfm 120mm intake
1 30cfm 92mm intake
1 25cfm 80mm exhaust
1 50cfm 92mm exhaust
1 25cfm exhaust

Intake = 98 cfm
Exhaust = 100 cfm

Wow I am good. I didnt even plan for it to be that close. I just used whatever was available.

Anyway, my theory is that it doesnt matter if your case is slightly positive or slightly negative; as long as its more or less equal, its all good. Now if you have double the intake than exhaust, or vice versa, then you have a problem. But as long as they are fairly equal, I'd say yiu're in good shape.
 
Well even is optimal, but blah to that....

pos vs neg.... i pick pos

why?

Because with negative pressure, every tiny crack there is in yuoru case, air is sucked in.... ie between cdrom drives and crap like that....

why is that bad?!?!
DUST.

You end up wiht dust in all these little damn spots.

Now if you have POS pressure, then you can put filters over all the intake fans, and your case gets alot less dusty!

Most of the dust is stoped by teh filters and doesn't sneak in thse little damn cracks, instead filted air is pushed out them.
 


<< I agree, slightly negative or even pressure would be the best... positive pressure is useless, since the hot exhaust air has nowhere to go >>



I've got lots of air going out.....well not sure actually, right now i have my case off since i'm in the middle of tweakng my new upgrade....but i will have lots more, since i ordered a 120mm delta :-D
 
Always have a little more in than out. I do have a couple of 80mm blowing the hot air out above the PAL8045 with the 50cfm sunon on top.
 
OK, I understand and agree about the negative pressure and dust, point well taken. However, his question was what is better for MAXIMUM COOLING. Positive pressure in the case will cause your temps to be higher, maybe not much higher, but higher nonetheless. I certainly would agree that if your temps aren't a problem, then try going with a slightly positive pressure. It will keep the inside of your case much cleaner... 😉
 
in most general situations, it really wouldnt matter. However in a computer case, the CPU/Heatsink sits right in front of the exaust fan. having a more negative pressure will be more efficient for the CPU since it will suck the hot air immediately as it comes off the heatsink instead of letting it mix with the rest of the air inside the case.

If the CPU was mounted near the intake like some AT chasis, perhaps having more positive might be better.

Overall, AMD even states that having a front intake is not necessary, and it can even circulate hot air instead of bringing cool air inside.
 
it really depends on your setup.

negative pressure gets very dusty but it cools just as well.

i used to have 2 120mm side panel fans and 1 120mm top blowhole fan in addition to my 80mm front intake and 80mm rear exaust.

i removed the 2 120mm side panel fans but of course had to leave the grilles in place.
no increase in temps at all! its now quieter, but dustier :disgust:
 
Well, I wonder if high pressure inside your case (higher density) would help overclock, to a certain degree. Wouldn't the higher density air be able to absorb more heat from the HSF?

Just a thought.

 


<< ...... Overall, AMD even states that having a front intake is not necessary, and it can even circulate hot air instead of bringing cool air inside. >>



Not meaning to argue but real world experience has shown that air intake helps in cooling.

As far as I can see this thread is misunderstood.

Positive or negative is in my experience a theoretical value applied to PC case cooling when a unknown vaule can not be determined.
It is just a simple way to arrive at 'good' airflow.
Trust me.....I have tried to calculate airflow. It just ain't easy considering the characteristics of an enclosure.

XZeroII,
It has already been said and is good advice...Thanks to Sundog

Establish the needed airflow and go from there.
Hereis some good info on calculating airflow, pressure, and noise.

Brent
 
a negative pressure system would be much less effective if you didnt have a hole/grille (in the side panel over the cpu) for a place to draw in fresh air. that way you would have 3 (or more) exaust fans "pulling" air in right over the cpu.

making the front lower fan an exaust fan doesnt usually work well too. either leave it empty or make it an intake fan.
 
I have 3 120mm case fans 1)bottom front (intake) 2) side panel right above cpu (intake) 3) top of case (exhaust)
I also have 3 80mm fans 1) right below power supply (exhaust) 2) mounted on bottom of power supply blowing in 3) psu fan
anyway to get to the point (besides the fact I don't care how loud my system is) I had negative pressure before I added the 120mm in the side panel. My temps decreased by about 5c on my cpu once I installed the 3rd 120mm. Of course I know it's because it's right above the cpu but I'm sure it would have helped anywhere I put it on the side panel.
 
heya dazed,

well thats kinda my point - did you have the 120mm hole in your side panel before you installed the 120mm fan?
in other words - did you try runnning with the 120mm hole in the side panel but w/o a fan there?

you might be surprised - and not actually need a fan there (just the hole) :Q
 
Thanks for all the great advice. I've gotten some really nice information. I've decided to play with it and try a slight negative pressure and see what happens. Temps are a bit of a concern for me, so I'm gonna see what kind of effect this has on my temps.
 
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