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CPU Heatsink Fan Blowing Directly onto Case Exhaust Fan

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  • Heatsinks
  • Cases
  • Fan
  • Overclocking
Last response: in Overclocking
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September 16, 2009 2:15:52 PM

Hi,

I'm upgrading my PC and have an interesting cooling situation that doesn't seem to follow the usual standards (front bottom intake, rear top exhaust). I've got a Silverstone TJ09 case, and since the power supply sits at the bottom of the case I've got the fans on the top blowing air into the case to move air from top to bottom and exhaust out the PS. For my new CPU I'm putting in, I'm installing the Noctua NH-U12P SE1366 heatsink. It comes with two fans for a push-pull configuration, and I'm wondering what the effects of having two fans close together would be (so that I can determine how to orient it). Basically, if I place it horizontally the push fan sits very close to the case's rear exhaust fan. Does the heatsink fan blowing air directly onto the exhaust fan negatively impact the air flow there? Alternatively I could install it vertically with the fans blowing air downward over the GPU and towards the PS, and I would just remove the case's top intake fan that sits directly above the heatsink.

I'd appreciate any help with the two fan's at close proximity situation, and I'd also be open to any alternative setups I may not have thought of here if those would work better. Thanks!

Edit; I've been told a couple times to switch my top fans to exhaust instead of intake, however that would leave me one intake fan in the 'front' of the case to the two top exhaust fans, rear exhaust fan, and power supply exhaust fans. I was hoping to even things out a bit.

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a b K Overclocking
September 16, 2009 7:03:45 PM

Go with what others have said - the top fan needs to exhaust. Hot air rises, you are fighting a losing fight there using it as a intake. Maybe adding some side fans or another front fan may help. Maybe you could upgrade the front fan to a higher CFM fan.

I have my cpu cooler's fan less than 2 inches from my rear exhaust fan, it works well in my experience.

Personally, I wouldn't route more hot air through the PSU.
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September 16, 2009 8:34:21 PM

I agree with festerovic, you want to follow the convention of hot air rising, also having the CPU cooler blow directly into an exhaust fan is actually a very good idea as it allows the heat generated from the CPU to vacate the case almost immediately which helps other parts remain cooler. You should add some more intake, but you should follow the standard convention as it works much better. Part of the advantage of placing the Powersupply on the bottom is that it doesn't pull in extra hot air, so I don't recommend cancelling it out.
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September 17, 2009 7:26:14 AM

Got it. Unfortunately there's only one mount on the front and none on the sides for other intake, however I was reading elsewhere that having both the front and rear fans working as intake and both top fans as exhaust works pretty well. I could then rotate the heatsink fans to blow directly up.
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a b K Overclocking
September 17, 2009 3:05:38 PM

Get a high cfm fan for the front then. Somebody could recommend one, I always use the ones that come in the case (not picky).
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a b K Overclocking
September 17, 2009 6:30:20 PM

#1 is 66db...omg.

But it is 246cfm...memorex commercial. :) 
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a b K Overclocking
September 17, 2009 11:45:08 PM

I have my CPU fan blowing directly out an exhaust as well.
However, I found with both fans on, the 140mm exhaust fan would slow down, and that the increase in airflow was neglagible.

I ended up disconnecting the 140mm exhaust, and the 92mm CPU fan works on it's own, without any difference. I do have other exhaust fans though, just didn't find running two fans closely in series to be worthwhile.

Less noise > tiny increase in airflow.

Obviously varies per application, you can tell if the pair flows more when both on or not.

Agree with others, top is exhaust due to heat rising, pushing down could cause hot pockets to build up in areas where air is not forced.
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September 18, 2009 9:04:06 AM

Unfortunately I can't seem to open those links here, but I think the final setup is going to be rear and top two exhaust fans, power supply pulling in air from the case exterior as opposed to inside the PC, and buying a newer intake fan in the front. The new intake fan only pulls in double the cfm that each of the exhaust ones do, but that's the best I could get set up with my current noise considerations. With rear and top exhaust it shouldn't make a huge difference whether or not the heatsink is oriented vertically or horizontally, and I can manually test whether removing one of the top fans makes any temperature difference.
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a b K Overclocking
September 18, 2009 2:45:53 PM

pagemaster500 said:
Unfortunately I can't seem to open those links here, but I think the final setup is going to be rear and top two exhaust fans, power supply pulling in air from the case exterior as opposed to inside the PC, and buying a newer intake fan in the front. The new intake fan only pulls in double the cfm that each of the exhaust ones do, but that's the best I could get set up with my current noise considerations. With rear and top exhaust it shouldn't make a huge difference whether or not the heatsink is oriented vertically or horizontally, and I can manually test whether removing one of the top fans makes any temperature difference.

How exactly are you planning on getting your PSU to be intake instead of exhaust? Do you plan on taking it apart? I wouldn't do that. Too many things could go wrong.

Top exhaust is great, since hot air rises. I'd say maybe the front and back as intake since you have dual exhaust on the top, but also you should play around with it. Try different configurations and see what gives you the best temps.
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September 18, 2009 6:34:16 PM

jedimasterben said:
How exactly are you planning on getting your PSU to be intake instead of exhaust? Do you plan on taking it apart? I wouldn't do that. Too many things could go wrong.

Top exhaust is great, since hot air rises. I'd say maybe the front and back as intake since you have dual exhaust on the top, but also you should play around with it. Try different configurations and see what gives you the best temps.


I probably should have specified a little more on the PS. My case is a Silverstone TJ09 which has a grille on the bottom for air intake for the power supply. The power supply isn't acting as an intake for the system, it's just taking in air from outside as opposed to inside the case. I definitely will be messing around with different configurations, however I just wanted to figure out viable options before ordering parts that may have been unnecessary. Thanks for all the advice!
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