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Lets talk about case cooling

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Rick James

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Joined
Jan 5, 2009
Location
Tempe, Az
Now i'm trying to get my fans to blow at optimal angles. Now the general consensus for the best cooling is to bring the air in from the bottom and shoot it out of the top correct? Problem is my PSU is on the bottom and is sucking air out SO the best thing for me to do is have the top mount 200MM fan bringing air in so that it will draw down towards the PSU correct?
 
And the case you are using is....?



Regardless of the case, it is normal to do intake in the front, exhaust in the back. Most people suggest (including myself) to have more intake then exhaust. Remember that your PSU is not going to move enough air to force you to change your other fan's orientation.
 
What are we talking about here... Antec 900/1200? I wouldn't change the way the fans push air in that case, there's a lot of in/out flow and having the PSU on the bottom keeps it out of the warmest part of the case and allows good flow out the back/top to get the hottest air in the case out as fast as possible. No good will come from fighting hot air that naturally rises and trying to exhaust all the hot air out of the psu(which can't handle the added air intake load).
 
And the case you are using is....?



Regardless of the case, it is normal to do intake in the front, exhaust in the back. Most people suggest (including myself) to have more intake then exhaust. Remember that your PSU is not going to move enough air to force you to change your other fan's orientation.

positive case pressure?

I personally like to run negative case pressure (more exhaust than intakes)... do in all my computers

It makes it easier to map out the flow of air over components and whatnot.

I think the best example is my server... 1 120mm fan @ 5v exhaust at the back and the psu's 80mm fan... Those 2 fans cool everything else as i have blocked off intake spots to just the bottom side and the front in front of the hd works like a charm.
 
positive case pressure?

I personally like to run negative case pressure (more exhaust than intakes)... do in all my computers

It makes it easier to map out the flow of air over components and whatnot.

I think the best example is my server... 1 120mm fan @ 5v exhaust at the back and the psu's 80mm fan... Those 2 fans cool everything else as i have blocked off intake spots to just the bottom side and the front in front of the hd works like a charm.

Biggest problem with negative case pressure is crap getting sucked in. If its too much every crack in your case becomes a vacuum.
 
I personally like to run negative case pressure (more exhaust than intakes)... do in all my computers

It makes it easier to map out the flow of air over components and whatnot.
That also pulls in dust into all the tiny little holes. Temperatures should decrease with positive pressure.
 
Plan and simple....

Intake through the front
Exhaust through the back

Intake through the bottom
Exhaust through the top
 
And the case you are using is....?



Regardless of the case, it is normal to do intake in the front, exhaust in the back. Most people suggest (including myself) to have more intake then exhaust. Remember that your PSU is not going to move enough air to force you to change your other fan's orientation.


Stuff I've read has suggested benefits of positive pressure, and supposedly one of them is less dust, though I can't see how.

That also pulls in dust into all the tiny little holes. Temperatures should decrease with positive pressure.

Way to go, I didn't read the whole thread. What you said makes perfect sense and now I understand why positive pressure works. All those tiny holes blow instead of suck, thus only dust comes in through the intake fans, and if you have filters, problem solved.
 
Stuff I've read has suggested benefits of positive pressure, and supposedly one of them is less dust, though I can't see how.
I won't claim to know for sure, but I think it is because there is more movement inside the case and that movement or positive pressure doesn't let the dust settle. At least that is all I can think of.
 
I won't claim to know for sure, but I think it is because there is more movement inside the case and that movement or positive pressure doesn't let the dust settle. At least that is all I can think of.

I edited my post with a response that seems to make sense. With a negative case pressure, you have a vacuum, and all those inlets that normally wouldn't move air start taking in air. Since the majority of high quality modern PC cases integrate some sort of filtration system at intake points, the problem would be greatly reduced, sure, you'll still want to clean your PC regularly, but the filters should take on most of the dust with a positive case pressure situation.

Also, the cooling is improved due to the nature of heats effect on air. It expands. The expansion causes the air to more readily move through the fans. Positive case pressure setups bring in more cool air, which is then expanded due to heat produced by your components, you have even more internal pressure. All this adds to the dust reduction properties of positive case pressure, as well.

Since the air is so tightly packed it more readily needs a method for escaping, moving through pores is a posibillity, but energy follows the path of least resistance, and well, hot air follows the same principal, doesn't it? Compressed air escapes through the compressed air can nozzle, not the bottom of the can which is sealed. The case I want has 1 exhaust fan, and 3 intake fans, with 2 fans inside helping to keep the momentum up after having been slowed down by the front fan systems filtration system.

PC-A70B by lian li. dual psu, simple looking, positive case pressure. :D

PC-A70BW_01.jpg


I use their picture because they seem to be the only one that carries the windowed version.

Testing in my armor showed that the fan placement that the lian li uses just past the hard drive cage improved my video card tempurature by almost 10 degrees celsius.
 
I have a Cooler Master sniper guys. I have..

1 200mm on the front blowing in
1 120mm on the bottom blowing in
2 120mm's on the door blowing in
1 120mm at the rear blowing out
1 200mm on top blowing out

Sound good? :)

Thanks again
 
Yes. that would bring more air than it would push out. Are your intakes mostly filtered?
 
I won't claim to know for sure, but I think it is because there is more movement inside the case and that movement or positive pressure doesn't let the dust settle. At least that is all I can think of.

this would be correct positive case pressure keeps the air "moving" .... but not in a way one would like... with positive case pressure you get lil hot spots of just circulating air due to the big amounts of turblance.
 
this would be correct positive case pressure keeps the air "moving" .... but not in a way one would like... with positive case pressure you get lil hot spots of just circulating air due to the big amounts of turblance.
Unless you have proper fan placement...this can keep going all day, lets just agree to disagree on preference for case pressure.
 
Unless you have proper fan placement...this can keep going all day, lets just agree to disagree on preference for case pressure.

I'll argue the point for you:

Look at the case I posted before. All the PC slots are vented, thus, any "pocketed air" would be forced out due to the pressure. Also, consider that most video cards nowadays are rear ventilated. Due to a pressure build up, these also would be able to pull in more air. Positive case pressure, in theory, improves the CFM of any exhaust fan because it doesn't have to pull the air at all, it just increases the momentum.
 
I'll argue the point for you:

Look at the case I posted before. All the PC slots are vented, thus, any "pocketed air" would be forced out due to the pressure. Also, consider that most video cards nowadays are rear ventilated. Due to a pressure build up, these also would be able to pull in more air. Positive case pressure, in theory, improves the CFM of any exhaust fan because it doesn't have to pull the air at all, it just increases the momentum.
You should be arguing with him, not me, lol. I agree with what you are saying.
 
That also pulls in dust into all the tiny little holes. Temperatures should decrease with positive pressure.

Positive case pressure PROPERLY DESIGNED is okay. Just adding a bunch of fans will lead to dead spots.

Negative case pressure will require more cleaning but should reduce temps (which is why you see so many PCs running for years with only one exhaust fan and no intakes)

Balance is what is usually deemed best and provides the coolest of temps.

It is really all up to the design of the case however.

If you are stuck with less exhaust points than intake points... you can use higher CFM fans as exhaust to try and bring it closer to balance....



Another thing to consider, positive case pressure leads to higher noise, and if too high will shorten the life of the fans.
 
Ok, you officially confused me. Going to break this down so it makes sense when I respond.

Positive case pressure PROPERLY DESIGNED is okay. Just adding a bunch of fans will lead to dead spots.
Agreed.

Negative case pressure will require more cleaning but should reduce temps (which is why you see so many PCs running for years with only one exhaust fan and no intakes)
I know there was a thread here that explained the physics behind positive case pressure vs negative pressure. Positive *should* have lower temps. Computers that have one exhaust fan run a long time because they don't put out a lot of heat, not because of the fan configuration.

Another thing to consider, positive case pressure leads to higher noise, and if too high will shorten the life of the fans.
You lost me. Higher noise = less lifetime?
 
Positive case pressure PROPERLY DESIGNED is okay. Just adding a bunch of fans will lead to dead spots.

Negative case pressure will require more cleaning but should reduce temps (which is why you see so many PCs running for years with only one exhaust fan and no intakes)

Balance is what is usually deemed best and provides the coolest of temps.

It is really all up to the design of the case however.

If you are stuck with less exhaust points than intake points... you can use higher CFM fans as exhaust to try and bring it closer to balance....



Another thing to consider, positive case pressure leads to higher noise, and if too high will shorten the life of the fans.

No it doesn't? Fans operate regardless of the pressure inside the case. It's not like we're forcing more air in than the fans could force into that space. And a fan would run at the speed it was set to run at regardless of interior pressure.

The only logic in your statement might suggest that positive case flow situations don't cool the computer as well, and will cause the computer to run warmer, and fans ran off the motherboard's fan controller will run at a higher speed. In theory, it's the other way around, negative case flow situations have to have the exhaust fans working harder. In a positive situation, more case fans at lower speed overpowering the exhaust fan means none of the fans work hard at all.
 
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