Case pressure: Positive or Negative

[Archangel1994]

Good day to you LTT community!

 

So I've decided on getting a Fractal Design Arc Midi R2 for my birthday and looking at it gave me a question. Seeing as how it can have 3 top and 1 rear for exhaust and 2 front 1 side for intake that would make negative pressure. When I look around for what the best pressure is I see either mixed results or people saying positive but not really explaining why so I would like a good answer now WITH A GOOD EXPLANATION! Which would be better for the Arc Midi R2 and why when it contains the parts I have listed in my sig (I5-2400, G1 gaming GTX 970, etc)

 

-Archangel

[AlwaysFSX]

Positive! You want to shove as much air as you can in instead of forcing the fans to pull air from where they can.

[Manny Calavera]

Positive pressure makes dust not go in small cracks.

[Totalschaden1997]

Positive! If there is negative pressure dust will be sucked in through non-filtered gaps/holes

[spwath]

Naw, it will be fine, you never want to occupy the front most 2 top slots.

[Archangel1994]

What's the difference in terms of performance?

[brownninja97]

I believe its better to have more intakes then exhausts, i have  3 intakes on my Z9 and two exhausts, it seems to work well.

[Lotus]

Positive will help with dust, while negative doesn't. Go positive if you care about dust.

[Si3Rra_7]

Negative is cooler , but it's dustier

Positive is less cool , but way less dust

[ForsakenLive]

Most systems we have rely on negative air pressure, notebooks and pre-built systems will almost always go with negative air pressure. Both will maintain the same temperature, the air that got inside the case and heated needs to get out asap, but it's useless getting a ton of exhaust if there is no real way to get more fresh air in, as the pressure needed will increase with the resistance.

Why do we want positive air pressure? If you have more intakes than exhaust you know for sure where does the air come from, and you can easily filter it. If you don't have filters or use very restrictive filters or you just don't bother cleaning them, positive air pressure is totally useless; this is exactly why notebooks and pre-builts use negative air pressure, at least they know the system will be able to keep running.

As other guys said, if you have a negative air pressure the fans won't be able to get enough air outside, so it will use every little hole, gap and crack there is to get more air until the path has more resistance than the static pressure the blades offer (making the fan not move air).

Finally, the amount of fans doesn't determine pressure, CFM mixed with static pressure does. Having 2 fans that intake against 3 that exhaust can be positive as long as the intake is getting more air (faster/better/bigger fans).

What's better for your system in terms of performance? As I said before, both are the same if they are properly balanced, it depends a lot on your fan configuration. In your case (Arc Midi R2), getting 2 powerful 140mm fans on the front (mind some extra noise) and using a rear and 2 top fans seems to be the easiest way to go, but you could also populate the bottom as intake.

[BaSkA]

This is really controversial and sometimes it has so many variables apart from what case you're using... I really recommend reading this thread as it helped me a lot and changed my mind on somethings I believed.

 

So, usually, negative pressure you have better temperatures as the hot air gets out from the case faster, as long as you have enough supply of fresh air. However, any cracks/gaps/holes on your case will be sucking air (read dust because there are no filters for cracks) in to try to compensate for the pressure inside the case.

 

Positive pressure, on the other hand, takes more time to exhaust the hot air from the case, having slightly better temperatures for short usage time and getting hotter on longer use. I'm not saying 10ºC difference, just about 2~3ºC usually. If not made properly, sometimes the intakes can be disrupting each other making hot bubbles in the GPU/CPU areas. However, it's the opposite of negative pressure regarding cracks as they will always be exhausting air, instead of sucking, to try to compensate for the pressure inside the case.

 

Either way, always have your intakes filtered. It's a good trade off for a slightly worse fan performance.

 

Now, to make the best choice, there's nothing better than experimenting. If you live at a dusty place, positive is probably the best idea. If you live at a hot place, without AC, negative might be the way to go. In either way, experimenting with fan layouts and pressure is the best thing to do.

Also, when I say negative/positive pressure, I mean a slight difference in CFM, not something HUGE. The best is to have "normal pressure" but it's rather difficult.

 

The setup I'll be doing on my rig is to have (slightly) positive pressure while on idle and, when the system is under load, a fan will spin faster so I have negative when I need the "best" temperatures. I'll copy this from a fellow forum member and the results seem to be really good.

 

 

P.S.: I do not have a way to prove this numbers/facts, it's just the opinion/knowledge I acquired after experimenting a bit with my old case and reading a lot of texts about this.

[RushTfe32]

This is really controversial and sometimes it has so many variables apart from what case you're using... I really recommend reading this thread as it helped me a lot and changed my mind on somethings I believed.

So, usually, negative pressure you have better temperatures as the hot air gets out from the case faster, as long as you have enough supply of fresh air. However, any cracks/gaps/holes on your case will be sucking air (read dust because there are no filters for cracks) in to try to compensate for the pressure inside the case.

Positive pressure, on the other hand, takes more time to exhaust the hot air from the case, having slightly better temperatures for short usage time and getting hotter on longer use. I'm not saying 10ºC difference, just about 2~3ºC usually. If not made properly, sometimes the intakes can be disrupting each other making hot bubbles in the GPU/CPU areas. However, it's the opposite of negative pressure regarding cracks as they will always be exhausting air, instead of sucking, to try to compensate for the pressure inside the case.

Either way, always have your intakes filtered. It's a good trade off for a slightly worse fan performance.

Now, to make the best choice, there's nothing better than experimenting. If you live at a dusty place, positive is probably the best idea. If you live at a hot place, without AC, negative might be the way to go. In either way, experimenting with fan layouts and pressure is the best thing to do.

Also, when I say negative/positive pressure, I mean a slight difference in CFM, not something HUGE. The best is to have "normal pressure" but it's rather difficult.

The setup I'll be doing on my rig is to have (slightly) positive pressure while on idle and, when the system is under load, a fan will spin faster so I have negative when I need the "best" temperatures. I'll copy this from a fellow forum member and the results seem to be really good.

P.S.: I do not have a way to prove this numbers/facts, it's just the opinion/knowledge I acquired after experimenting a bit with my old case and reading a lot of texts about this.

This.

Totally agree with you, not a better way to explain it.

I don't like positive, because I live in a very hot place, I need hot air to go away very quick from my computer. Air bubbles under my gpu could be a disaster. If you are using a negative, it's important to have very good fans as exhaust, highest static pressure. And higher cfm as you can buy. But static pressure is very important in order to do a good air flow inside your case.