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Negative vs Positive air pressure?

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April 8, 2014 12:21:08 PM

Hello,
I am thinking about purchasing some new fans for my Corsair Carbide 300r case in order to keep it cool as I have heard that the cooler the case is, the longer the PC will last. I have decided to get the Corsair AF and SP fans but I am unsure of whether to have negative, neutral or positive air pressure in the case. I have heard that negative air pressure is good as it keeps the PC cool but sucks in dust and that positive is also good as it keeps dust out but it does not provide as much cooling? The case I have has an 140mm front intake fan and an 120mm back exhaust and I was looking at putting an 120mm front intake fan with the other 140mm one and also adding an 140mm exhaust fan at the top of the case.

Any thoughts?
Thanks

Best solution

April 8, 2014 12:31:09 PM

Positive pressure - more intake than exhaust
Negative pressure - more exhaust than intake

Both of them have valuable advantages.
Positive pressure gets you less dust inside your case, but it is a bit against the laws of physics; hot air has bigger volume, so getting lots of intake fans and less exhaust fans means that the hot air is not effectively pulled out of the case and the cooling performance is worse.
Negative pressure is pretty much the opposite: better cooling performance but more dust.
Neutral pressure is of course something in between.

So I think it's up to your preferences.

Hope I helped.
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April 8, 2014 12:32:36 PM

in my experience if you have a good airflow case and propper fans there is almost no difference in temps between positive and negative pressure. in a case with poor airflow, generally you'll see a small advantage going with negative pressure.

If you live in a dry, dusty climate, it's almost required to go with positive pressure. as the dust buildup is extraordinary with negative in places like phoenix or other like places in the SW.

KrzysiekX10 said:
Positive pressure - more intake than exhaust
Negative pressure - more exhaust than intake

Both of them have valuable advantages.
Positive pressure gets you less dust inside your case, but it is a bit against the laws of physics; hot air has bigger volume, so getting lots of intake fans and less exhaust fans means that the hot air is not effectively pulled out of the case and the cooling performance is worse.
Negative pressure is pretty much the opposite: better cooling performance but more dust.
Neutral pressure is of course something in between.

So I think it's up to your preferences.

Hope I helped.

the example cited above (about positive pressure) is only true if your case lacks top ventilation. I have an antec 902... it's set up with a positive pressure. however it still has excellent ventilation due to the big 200mm fan on the top of the case. Just because i'm drawing a LOT of air into the case doesn't mean i can't be venting a LOT of air too. In my experience a case with excellent airflow trumps a case without 10 times out of 10 no matter how it's set up.
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April 8, 2014 12:35:00 PM

KrzysiekX10 said:
Positive pressure - more intake than exhaust
Negative pressure - more exhaust than intake

Both of them have valuable advantages.
Positive pressure gets you less dust inside your case, but it is a bit against the laws of physics; hot air has bigger volume, so getting lots of intake fans and less exhaust fans means that the hot air is not effectively pulled out of the case and the cooling performance is worse.
Negative pressure is pretty much the opposite: better cooling performance but more dust.
Neutral pressure is of course something in between.

So I think it's up to your preferences.

Hope I helped.


Okay thanks, I may go neutral then as my case does have fairly good airflow but it can get quite dusty due to the room it is in.

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April 8, 2014 12:37:48 PM

ingtar33 said:
in my experience if you have a good airflow case and propper fans there is almost no difference in temps between positive and negative pressure. in a case with poor airflow, generally you'll see a small advantage going with negative pressure.

If you live in a dry, dusty climate, it's almost required to go with positive pressure. as the dust buildup is extraordinary with negative in places like phoenix or other like places in the SW.


the example cited above (about positive pressure) is only true if your case lacks top ventilation. I have an antec 902... it's set up with a positive pressure. however it still has excellent ventilation due to the big 200mm fan on the top of the case. Just because i'm drawing a LOT of air into the case doesn't mean i can't be venting a LOT of air too. In my experience a case with excellent airflow trumps a case without 10 times out of 10 no matter how it's set up.


Okay thanks. I think im gonna get an 120mm fan on the front and then an 140mm fan on the top which will make the case neutral pressure wise. I live in Scotland so dusty environment isn't much of an issue. Also what do you think about the fans I have chosen?
Thanks again

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April 8, 2014 12:41:34 PM

reubenno said:
ingtar33 said:
in my experience if you have a good airflow case and propper fans there is almost no difference in temps between positive and negative pressure. in a case with poor airflow, generally you'll see a small advantage going with negative pressure.

If you live in a dry, dusty climate, it's almost required to go with positive pressure. as the dust buildup is extraordinary with negative in places like phoenix or other like places in the SW.


the example cited above (about positive pressure) is only true if your case lacks top ventilation. I have an antec 902... it's set up with a positive pressure. however it still has excellent ventilation due to the big 200mm fan on the top of the case. Just because i'm drawing a LOT of air into the case doesn't mean i can't be venting a LOT of air too. In my experience a case with excellent airflow trumps a case without 10 times out of 10 no matter how it's set up.


Okay thanks. I think im gonna get an 120mm fan on the front and then an 140mm fan on the top which will make the case neutral pressure wise. I live in Scotland so dusty environment isn't much of an issue. Also what do you think about the fans I have chosen?
Thanks again



they're solid fans... unremarkable excepting for the pretty colored rings you can put on them (that's not a knock on them... they're good fans... just not "amazing").

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April 8, 2014 1:11:44 PM

ingtar33 said:
reubenno said:
ingtar33 said:
in my experience if you have a good airflow case and propper fans there is almost no difference in temps between positive and negative pressure. in a case with poor airflow, generally you'll see a small advantage going with negative pressure.

If you live in a dry, dusty climate, it's almost required to go with positive pressure. as the dust buildup is extraordinary with negative in places like phoenix or other like places in the SW.


the example cited above (about positive pressure) is only true if your case lacks top ventilation. I have an antec 902... it's set up with a positive pressure. however it still has excellent ventilation due to the big 200mm fan on the top of the case. Just because i'm drawing a LOT of air into the case doesn't mean i can't be venting a LOT of air too. In my experience a case with excellent airflow trumps a case without 10 times out of 10 no matter how it's set up.


Okay thanks. I think im gonna get an 120mm fan on the front and then an 140mm fan on the top which will make the case neutral pressure wise. I live in Scotland so dusty environment isn't much of an issue. Also what do you think about the fans I have chosen?
Thanks again



they're solid fans... unremarkable excepting for the pretty colored rings you can put on them (that's not a knock on them... they're good fans... just not "amazing").



Okay, are there any else you would recommend for around £10 per fan?
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April 8, 2014 1:16:57 PM

at the £10 mark? probably not. if you're getting them for £10 each thats actually a good deal. i'm now a little more positive about the buy.

the only fans i might suggest instead would be more expensive (Scythe Gentle Typhoon AP-15, or pick your fav Noctua)... so for £10 it's a good buy.
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April 8, 2014 1:34:43 PM

Okay, I'll go ahead and get them then, thanks for the help!
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April 8, 2014 1:35:49 PM

Hi -
Once you get set up, be sure to check if there is any impact on the airflow across your PSU and/or graphics card. I was running my machine for some time with all the fans running at full, and then I realized that the outflow fans were overpowering the inflow fans to the point where the outflow was pulling air *backwards* through both my PSU and my graphic card.
I switched down the speed on the outflow fans, and I'm still keeping good temps but no longer forcing air through the PSU and graphics card against the natural flow.

Hope this helps.
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April 8, 2014 2:01:28 PM

Okay I'll keep that in mind, thanks very much!
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