[mythtv-users] Fans and cooling

David Brodbeck gull at gull.us
Tue Aug 28 18:28:57 UTC 2007

On Aug 28, 2007, at 10:40 AM, Jay R. Ashworth wrote:
> In general, fans should blow *onto* the components they're cooling, as
> power supply fans do (they cool *the power supply*).

I don't think I've ever seen a PC power supply that worked that way.

The ones I've seen have an exhaust fan that pulls air *out* of the  
power supply.  The idea seems to be to create a slight negative  
pressure that will pull air through the computer case (and the power  
supply internals.)  Modern machines generally have additional case  
fans that blow air into the front of the case, but it used to be the  
power supply fan sucking air through the front panel vents was the  
only way hard disks got any airflow.  This is why it was generally  
considered a bad idea to run a computer with the cover off.

I agree, though, with your general point.  If you're trying to cool a  
particular component, it's most effective to pull air from outside  
and blow it onto that device.

This doesn't come up much in home installations, but when you put a  
lot of machines next to each other, it also starts to become pretty  
important that they all move air in the same direction.  I had one  
Dell tower that had a CPU fan that sucked air in through a vent on  
the back panel.  Unfortunately, this meant the CPU got cooled by the  
hot air exhausted by all the other machines' power supplies!

In general I'm not impressed by the airflow design of most PCs.  It  
seems to be a brute force approach with little engineering effort  
behind it.  It's interesting to take apart an old IBM PS/2 and look  
at how carefully they channeled the air to make sure it flowed over  
all the internal components before eventually being exhausted by the  
power supply.

More information about the mythtv-users mailing list