# PSU Fan: Exhaust or intake



## Phu

I have an Aspire Chameleon 550W PSU which has a 120mm intake fan blowing down upon my CPU.  I was thinking about opening up the PSU (I am fully aware of the safety issues) and simply flipping the fan, essentially making it an exhaust.  From what I can gather most people recommend using fans at the back of the computer for exhaust anyway and the aspire has got to be a bad source of dust when used as an intake.  Has anyone ever tried this?  By the way, I use a Zalman 7700 120mm CPU heatsink and I am not having overheating issues at all.


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## heinzbitte

So what you are saying is that your power supply takes air from the outside of the case and blows it in?? Wouldn't that blow hot air into the case?


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## 691175002

The ATX (or whatever) spec says that the psu should blow air in over the cpu to help cool it.  In theory it souds good but they didn't think about the heat the psu would generate.  Now most new psu's blow air out of the case because in some cases the air blowing "to help cool the cpu" was actually making it hotter.

What you have done should be fine and may help too.


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## Praetor

> I have an Aspire Chameleon 550W PSU which has a 120mm intake fan blowing down upon my CPU. I was thinking about opening up the PSU (I am fully aware of the safety issues) and simply flipping the fan, essentially making it an exhaust. From what I can gather most people recommend using fans at the back of the computer for exhaust anyway and the aspire has got to be a bad source of dust when used as an intake


PSUs arent supposed to do that... are you sure the PSU has an intake fan?



> The ATX (or whatever) spec says that the psu should blow air in over the cpu to help cool it


1. What page?
2. How do fanless ATX compliant PSUs do this?



			
				ATX Specification said:
			
		

> The ATX Specification allows for numerous (and often confusing) possibilities for power
> supply fan location, direction, speed, and venting. The designer’s choice of a power supply
> cooling solution depends in part on the targeted end-use system application(s). At a
> minimum, the power supply design must ensure its own reliable and safe operation.
> 
> Fan location/direction. In general, exhausting air from the system chassis enclosure via a
> power supply fan at the rear panel is the preferred, most common, and most widely
> applicable system-level airflow solution. Other solutions are permitted, including fans on
> the topside of figure 5 and the Wire harness side of figure 4 or 5. Some system/chassis
> designers may choose to use other solutions to meet specific system cooling requirements.





			
				ATX Specification said:
			
		

> The ATX Specification offers two options for venting between the power supply and the
> system interior:
> • The venting shown in Figure 8 provides the most effective channeled airflow for the
> power supply itself, with little regard for directly cooling any system components. This
> venting method is nearly always used in conjunction with a fan that exhausts out the
> rear of the power supply.
> 
> • The venting shown in Figure 9 allows designers to more directly couple the power
> supply airflow to system components such as the processor or motherboard core,
> potentially cooling all critical components with a single fan. Both the power supply fan
> location and direction may vary in this case. The trade-off is usually one of reduced
> system cost versus narrower design applicability.


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## 691175002

Well I don't know... I just read it somewhere a while back and put it here.  Either way from reviews none of the "silent psu's" can conform to the atx spec and one even blew up (so much for not emmiting any startling noises of smokerofl)(that would be from the custom pc december 2004 issue).


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