Case Airflow: Positive or Negative

[Lemonlust]

Positive - When there is more fresh air coming into the case than being exhausted out of the case.

Negative - When there is more air being exhausted out of the case than air being taken into the case

What's better for cooling positive or negative air pressure? What are some of the pros and cons of both?

[Uggorthaholy]

It's not really possible to achieve neutral airflow.

Negative is preferred because it prevents dust buildup, IIRC.

[Skelly]

It's not really possible to achieve neutral airflow.

Negative is preferred because it prevents dust buildup, IIRC.

Other way around.. Positive pressure means the air in your case wants to escape.. Negative pressure means air wants to get in, so air will be sucked in through any openings that don't have fans on then which may or may not have filters on them.

[Deleted]

I use a possative airflow at the min because of case design, i'm using 1 120mm at front, 1 side mounted 120mm case fan and i use a single 120mm rear fan.

Both intake fans have dust filters but they still need a clean every now and again. I'd prefer a bigger case with 1/2rear 120mm fans and a roof fan and just use 1 intake fan at the front to get some fresh air in the system.

[Uggorthaholy]

Other way around.. Positive pressure means the air in your case wants to escape.. Negative pressure means air wants to get in, so air will be sucked in through any openings that don't have fans on then which may or may not have filters on them.

That's the one. I always mix them up. WTB a revote :-p

[Rixis]

i have 2x 200mm and 2x 120mm, 1 of each for intaking and exhausting, it's as close to neutral as i'm likely to get (the pairs of fans are the same and all running at the same speeds), otherwise, at this current moment, i have no temperature or dust problems, so not all that fussed

[BicycleMafioso]

Tip it over to positive. You'd rather have more air coming in than going out, else it starts leaking in everywhere, where you don't have filters.

General rule is not to overdo it either way.

[Cryless]

Positive prevents dust buildup.

[Lemonlust]

Since hot air rises should I switch my rear exhaust to intake? and let my Two 120mm top fans do the exhausting? I have a 200mm side intake and two 120mm intakes in the front.

[styopa]

If you have fans pushing air into the case, so you have higher pressure in the case ("positive" pressure), those fans are taking the air from somewhere, ie the world, ie air full of dust.

If you have fans pushing air out of the case, so you have a slightly lower pressure in the case, air is going to infiltrate the case through every crevice in the case, pulling in dust with it.

Either way, the difference is trivial.

That said, all else being equal, positive pressure is probably marginally better.
1) you can control where air is coming in; you can put filters over these specific points and make sure minimal dust is infiltrating into your case.
2) The best insulator in the world is a vacuum. Ergo, reducing the air pressure in your case moves it *marginally* toward a vacuum, ie lower efficiency in heat transfer away from your cooling vanes, etc. It's probably even below the level of being able to be measured, but my bet is that a case with lower pressure inside is going to shed head slightly less well.

In my case, however, I use negative pressure. Why? Because of airflow. Positive pressure fans blow air in a pattern into your case, causing eventually a stable pattern of air currents. This means certain areas get cooled better than others. Certainly, convection of the air will somewhat disrupt this, but generally a hot case will stabilize with certain airflow patterns. I can't afford that. Everything in my case runs hot, so I need airflow from all directions. Having negative pressure both causes airflow in from multiple directions, it is less likely to stabilize in a pattern. I get marginally better cooling with negative than positive.

[BicycleMafioso]

Since hot air rises should I switch my rear exhaust to intake? and let my Two 120mm top fans do the exhausting? I have a 200mm side intake and two 120mm intakes in the front.

But how far would the rear-intake move air before it got exhausted again? Intakes are generally preferred bottom/front, and exhaust back/top. Side can go either way. What case do you have, and what slots in it have you populated?

[DeltrusDisc]

Positive, I stand with my regular pals here as usual. Get it as close to neutral though as possible.

Here's my situation:

I have a HAF X (loltetrishatesme) with a 230mm intake on the front, bought new fans for all the other sides: 200mm out-take on side, 2 of them on front, and a 140mm out-take on back. To fix the negative airflow issue this would cause: 230mm is at 100% (still not loud at all since it is such a huge fan), all others at a low 40%.

---------- Post added 2011-09-23 at 01:14 AM ----------

If you have fans pushing air into the case, so you have higher pressure in the case ("positive" pressure), those fans are taking the air from somewhere, ie the world, ie air full of dust.

If you have fans pushing air out of the case, so you have a slightly lower pressure in the case, air is going to infiltrate the case through every crevice in the case, pulling in dust with it.

Either way, the difference is trivial.

That said, all else being equal, positive pressure is probably marginally better.
1) you can control where air is coming in; you can put filters over these specific points and make sure minimal dust is infiltrating into your case.
2) The best insulator in the world is a vacuum. Ergo, reducing the air pressure in your case moves it *marginally* toward a vacuum, ie lower efficiency in heat transfer away from your cooling vanes, etc. It's probably even below the level of being able to be measured, but my bet is that a case with lower pressure inside is going to shed head slightly less well.

In my case, however, I use negative pressure. Why? Because of airflow. Positive pressure fans blow air in a pattern into your case, causing eventually a stable pattern of air currents. This means certain areas get cooled better than others. Certainly, convection of the air will somewhat disrupt this, but generally a hot case will stabilize with certain airflow patterns. I can't afford that. Everything in my case runs hot, so I need airflow from all directions. Having negative pressure both causes airflow in from multiple directions, it is less likely to stabilize in a pattern. I get marginally better cooling with negative than positive.

This is a very very very intriguing and well-put post. I give you props.

[Lemonlust]

So it all depends on how your case and hardware is setup?

[Senicide]

more in then out get fan filters there cheap and good cases come with them

[Deafyx]

So since there is a thread started, and I have always wondered if my case could be improved, here is what I have.



I have a CM HAF-X. Intake is from the front 200 and the side 200, while the output is from the P/P from my H50 and one top 200 fan. Is this optimal for me? I could purchase another 200 fan and put it up top, but I do not know if Ill have TOO much output than intake? Oh, and the side fan runs REALLLLY slow imo, so I am not quite sure if its really doing too much.

Both intake fans of filters btw

[DeltrusDisc]

MOAR FANS!!!

Honestly, just control the different amounts. ;p Making your case less like the original is always nice, and new fans > stock fans. ;p Though it seems kind of difficult to find a fan that will go on the side and act as an intake. =/ I have one on the side, a Xigmatek, problem is it only has one side with slots for screws, so while it was miles easier to install, it only gave me one option. >_< That was out-take. I'd say put another on top and then put your two top fans at like 50% or so, with your in-take fans at 70%, Since you also have the fans for the P/P.

[Deafyx]

MOAR FANS!!!

Honestly, just control the different amounts. ;p Making your case less like the original is always nice, and new fans > stock fans. ;p Though it seems kind of difficult to find a fan that will go on the side and act as an intake. =/ I have one on the side, a Xigmatek, problem is it only has one side with slots for screws, so while it was miles easier to install, it only gave me one option. >_< That was out-take. I'd say put another on top and then put your two top fans at like 50% or so, with your in-take fans at 70%, Since you also have the fans for the P/P.

None of my fans are stock except for the one on top and the side since the side fan will sooner or later be gone for the new side panel that will be going on it. :P

[DeltrusDisc]

None of my fans are stock except for the one on top and the side since the side fan will sooner or later be gone for the new side panel that will be going on it. :P

ohhh. What kind of side-panel? And where did you get it? Link!!!

[Deafyx]

ohhh. What kind of side-panel? And where did you get it? Link!!!

This is the side panel I plan on purchasing.

Linky

[murphymurph]

The new Antec 900 series is probably the best bang for your buck, and only $99. Positive airflow is the preferred way, the 900 puts the PSU in the bottom front and discs/mobo are in the back right next to the biggest fan. The more fans and the more continuous airflow the better you are for cooling and dust reduction.

newegg.com/Product/Product.aspx?Item=N82E16811129021[