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Air Cooling - Changing Fan To Pressurize Case?

Tags:
  • Heatsinks
  • Cooling
  • Fan
  • Cases
  • Overclocking
Last response: in Overclocking
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May 25, 2012 2:49:46 PM

Hi -

I'm not overclocking, but this looks like the thread for cooling questions. Hope I'm in the right spot.

I'm thinking about turning one of my case exhaust fans around backwards to pressurize the case rather than exhaust.

I recently discovered that when I turn the top exhaust fan to full, it is strong enough to pull air backwards through the power supply. It seems like this would put an exceptional strain on the power supply fan, which is trying to exhaust, and then having air forced in the opposite direction. Oh, yeah, and then I checked my graphics card, and the top fan on max forces air backwards through it as well.

My setup is a bit older, but still very functional for my family. It's a homebuilt system:
Core i7 920 at 2.67 GHz Socket 1366 - no overclocking, stock Intel heatsink and fan
EVGA graphics card - NVidia GTX 275
PSU - Corsiar HX 1000W with a 120mm exhaust fan.
6GB RAM
Windows Vista 64
Antec 902 case
- Top - 200mm exhaust fan
- Rear - 120 mm exhaust fan
- Side - 120 mm intake fan
- Front - two, 120 mm intake fans

To clarify, the reverse-air flow condition occurs when the top exhaust fan is running at high, the rear exhaust fan is running at low, and the three intake fans are all running at maximum. When I adjust the top fan so that there is no forced reverse-flow over the PSU, the CPU can run as hot as 75 degrees Centigrade, if I've been pushing it hard. I'm not getting any BSODs. I keep the dust filters clean.

I am looking for the simplest solution, and so re-mounting the rear fan as an intake seems to be the easiest approach. I guess I'll need to put a dust filter of some kind over it, now that I'm thinking about it more.

Is there anything else I should consider or think about?

My only concern is that the exhaust from the PSU and graphics card could be pulled as intake by the re-mounted rear fan. Should I be concerned about this?

Thanks!
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a c 140 K Overclocking
May 25, 2012 3:18:14 PM

Exactly what is the problem you are trying to fix?

Older i7-920 chips did run a bit hot, particularly when overclocked.
So long as you are not getting any failures, or reduction in multiplier, nothing really needs to be done.

Take the time to verify that the stock cooler is mounted properly. Look at the back of the motherboard and verify that all 4 pushpins are completely through and locked. A slightly off mount can cause your problem.

If you want to improve things, I think you would be best advised to replace the Intel stock cooler.
Look at something like the cm hiper212 which is only $20. It will run cooler and quieter.

Your psu is very strong, and a bit of overkill. That is not bad, but since it will be loafing all the time, the psu fan will not need to run, or at least it will not need to spin up to high rpm. The job of the psu fan is to protect the psu, not to provide any case cooling. When you speed up the top fan, the psu sees sufficient airflow so there is no need to run the fan. That is not bad.

The purpose of case fans is to get hot air generated inside the case out of the case. Your case is doing this very well as designed.
Reversing the rear fan is more likely to screw things up. Try it if you want; it is not hard to change it back.
Running case fans at top speed will increase noise, and is not usually necessary.
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a b K Overclocking
May 25, 2012 5:00:59 PM

I run a 920 overclocked system (4ghz). My thoughts have always been to exhaust slightly more air than you supply. This provides a natural state for the heated case air to exit the system. It also creates the accumulation of dust on the outside of the case filters. It is my opinion and experience after many years of system building that for air cooling a slight negative case pressure is the way to go.
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June 6, 2012 7:57:53 PM

Best answer selected by GorfTheFrog.
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June 6, 2012 8:15:07 PM

Many thanks to for all the replies, but I appreciate geofelt's initial challenge, "Exactly what is the problem you are trying to fix?" along with his thoughtful comments.

I guess w/ no BSODs and adequate performance, maybe I don't really have a problem! :) 

I was working on two assumptions: cooler is better, and reverse air flow across my PSU and graphics card were bad (b/c of the stress on the fans, don't want to burn out the motors.)

So ... if I just don't crank up the exhaust fans, and as long as I don't get any BSODs, maybe I should just not be concerned about it.

But because I probably can't help but tinker, I'm likely to re-mount the rear exhaust fan and see if that makes a difference. Everyone here seems to agree that the Intel stock cooler is just barely not useless, so I might replace that as well. Thanks for the reference on the Cooler Master Hyper 212, but my motherboard is vertical, and some folks have posted that the 212 is a bit heavy and may warp the motherboard. Not sure about this.

Thanks again!
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