# Cases and Positive Pressure



## Izliecies (Nov 2, 2009)

Hello there again, I want to talk with guys about positive pressure in cases. I have some questions and maybe someone else will find this topic interesting too 

So I saw this video: http://www.youtube.com/watch?v=Qe-2ZqmSGug&NR=1
Then went to their page: http://www.silverstonetek.com/tech/wh_positive.php?area=usa

Positive pressure is all about keeping the dust out from your PC as you can I see in the video I provided. I think that that is quiet impressing - I liked the part when that guy blew the dust into case and it was blown out right away.

Question 1: As we know, heat rises, but if we want to keep our cases free from dust, SilverStone advises to make the top fan an intake fan. I think that this could be perfect in watercooled systems as the heat (AFAIK) is transported somewhere else. Is that so?

Question 2: What if I add side panel fans?

Also post your ideas or whatever comes in your minds.

I hope for an interesting conversation.


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## MRCL (Nov 2, 2009)

Let me tell you my story. I (used to) have a Silverstone Forstress case. 180mm front and top intake fans, one 120mm back exhaust. Now, being the smartass I am, I said to myself: Heat rises, so Imma gonna make that top fan exhaust rather than intake. So I actually had negative air pressure in the case then. BUT: Out of curiosity, I changed the top fan back to intake, making the whole thing positive pressure again. And blammo. Temps dropped considerably. It is dependant on the case, but personally I try to establish a positive pressure in all my cases (well, one atm ). 

The advantages are simple:
- More fresh air coming in
- Less dust will be sucked in
- Not really an advantage, but the rear exhaust fan wouldn't actually be needed, as the air presses itself out of the case, so far my understanding

Now, with side panel fans, you will add more airflow into the case, which would be good, but it can also mess up the flow direction, causing the air to stay longer in the case, which heats up everything again.


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## Sasqui (Nov 2, 2009)

My opinion... doesn't matter, as long as you have good airflow in the right places.  That will vary from case to case.  Dust will get in no matter what you do.


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## erocker (Nov 2, 2009)

Positive pressure, negative pressure dust will build up, there's no way around it. Hot air rises, top fans should be exhaust. In a traditional airflow sense, front and side fans are intakes, top and rear fans are exhaust.


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## Izliecies (Nov 2, 2009)

Thanks for your input!

How about dust filters on the intake fans? Are they needed when the pressure is positive?
What fans do you have in your Cosmos S right now?


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## erocker (Nov 2, 2009)

Dust filters kill airflow and is counterproductive to having a fan. It's best to blow the dust out of your case with compressed air every month or so.


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## MRCL (Nov 2, 2009)

Izliecies said:


> Thanks for your input!
> 
> How about dust filters on the intake fans? Are they needed when the pressure is positive?
> What fans do you have in your Cosmos S right now?



Well.. all fans are 120mm. There are two at the front pushing in with a rad sandwiched in, and six at the top exhautsing with a rad sandwiched in , one exhaust and one pointed at the northbridge. The case is open at the moment, and with winter coming along, temps are pretty nice. However in the hot summer days its a bad layout.


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## choppy (Nov 2, 2009)

hmm , id like to know too, ive just bought an antec 300 which i havent opened up yet. i was just going to make the top fan an exhaust fan ..... but form what ive seen...it should be an intake?  what role does the side fan play then?


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## Izliecies (Nov 2, 2009)

So I guess I will just have to try for myself, people have totally opposite opinions here


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## choppy (Nov 2, 2009)

well see. i thought air needed to be 'pulled' through the case, the 120mm pulls it in , and the top/side/back fans pull it through and out of the case, therefore causing air to 'flow' . i mean in theory it sounds about right?


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## zenlaserman (Nov 2, 2009)

I've always found negative pressure with top-mounted exhaust fans to be the most efficient at cooling hardware in a case.  You'll get fresh air from more points on the case, which usually means more complete cooling.  Of course it also tends to draw in more dust, especially if you do the big no-no of putting your PC directly on carpet (raise it up at least 3 inches!).

To each their own tho.


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## MKmods (Nov 2, 2009)

Thanks Izliecies for that link.

To me personally making airflows path as simple/straight/short as possible is superior.

I never focus on pos or neg, just getting air in, past the heatsinks and out.


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## Bundy (Nov 2, 2009)

I have a different approach. I have 4-5 fans pushing filtered air into the case but only two pulling out. I use twice as many blowing in because the filters knock the intake flow down a lot. The overall case pressure is still slightly positive so that the dust is kept out and all I need to do is clean filters every few weeks.

I have another case that runs negative pressure. It continually fills the USB ports (any any other hole) up with dust. My feeling therefore is that slightly positive pressure is best, too much positive or negative pressure means your fans are working less efficiently.


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## Velvet Wafer (Nov 3, 2009)

*cough*Benchcase.*cough*


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## choppy (Nov 3, 2009)

okay, i cant believe im about to say this....well as i was putting some new ram into my pc, i thought of this thread and and decided to make my side fan an intake fan instead of exhaust. 

my temps? theyve actually dropped by a good 5-6 degrees. my cpu idles about 38-39, whereas before it was like 45-46


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## [Ion] (Nov 3, 2009)

choppy said:


> okay, i cant believe im about to say this....well as i was putting some new ram into my pc, i thought of this thread and and decided to make my side fan an intake fan instead of exhaust.
> 
> my temps? theyve actually dropped by a good 5-6 degrees. my cpu idles about 38-39, whereas before it was like 45-46



Yep, this is what I generally do.  Front, side and bottom for intake (the case has to be raised up though), and top/back for exhaust.  Gives me the best temperatures with minimal dust


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## Zedicus (Nov 3, 2009)

o man not again.

your never going to get positive or negative pressure built up in a case by using case fans.
EVER.

you want to maximize your airflow and make it as smooth and efficient as possible.  

filters are great, if you account for them.

fans that are very close together, like 1 right above or next to the other, are not doubling the claimed output.  2 37cfm fans right next to each other is not 74cfm.  

having more fans in or out is not important, balancing the flow is, which is why when some of you turned a fan around and dropped 5 degrees all you did was 1. smooth out the flow characteristics. and 2 equalize in and out cfm. 

too much airflow in and too much pulling air out will both drastically reduce efficiency.   you want the air to sweep through your case like a river, in in the front bottom, out on the top back.  if you have massive videocards spewing heat they should rear exhaust, but that needs to be accounted for with other fans.  like a side case fan over the video cards.then you will end up with 2 airflow channels that dont mix.  

you only want a side case fan over the cpu if you are separate channeling it also.

top fans are not important unless some other airflow streem is too far out of sink intake or outlet side.


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## Disparia (Nov 3, 2009)

Was a good move for my little girl's system. (Rear 120mm is blowing in)

House is too dusty to not use filters, but luckily that fan provided good airflow when using a mesh filter.


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## vega22 (Nov 3, 2009)

im a top and rear out, front side and bottom in kind of guy too


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## RaPiDo987 (Nov 3, 2009)

*my set up..*

This is my air flow set up...



Feedback?


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## Bundy (Nov 3, 2009)

That looks quite good. Where does your dust collect? I think that if it's mainly on the filters, you have the ratio spot on, if not, look for another spot to put a filtered intake fan (side?).


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## pantherx12 (Nov 3, 2009)

marsey99 said:


> im a top and rear out, front side and bottom in kind of guy too




To me that sounded filthy


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## choppy (Nov 4, 2009)

okay call me stupid, but what can i use to raise a case 3 inches , thats free and can still make it look normal / good ?


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## Velvet Wafer (Nov 4, 2009)

choppy said:


> okay call me stupid, but what can i use to raise a case 3 inches , thats free and can still make it look normal / good ?



sanded,laquered pieces of wood


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## sneekypeet (Nov 4, 2009)

Good answer, i have also been known to use spare 2X4, bricks, books, boxes....get out the tape measure and start looking for pairs of something


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## choppy (Nov 4, 2009)

Velvet Wafer said:


> sanded,laquered pieces of wood



i can do sanded wood... but isnt lacquer flammable ?


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## sneekypeet (Nov 4, 2009)

choppy said:


> i can do sanded wood... but isnt lacquer flammable ?



If you have a fire under your chassis, the laquer isnt the issue


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## Nailezs (Nov 4, 2009)

rofl that was good


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## Velvet Wafer (Nov 4, 2009)

sneekypeet said:


> If you have a fire under your chassis, the laquer isnt the issue



make it really smooth (up to 500 grit),and laquer it in the same color that the case is.
ready no fire to start


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## douglatins (Nov 18, 2009)

That doesnt make sense to me, I previosly had 2 120mm fans in my 2nd comp both at 1200RPM, the filter got disgusting dirty so i remove the front fan and replace the back for a more powerful 2000RPM fan, now the air that comes out is way cooler. Though i didnt opened to see the dust.

This positive thing only removes the dust coming from the holes in the case, but they will still get inside through the filters, because no filter prevent 100% of dust


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## kocoman (Nov 21, 2009)

Is it possible to add a air pressure monitor to the computer?


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