CPU Fan airflow Direction

[rdege]

My question relates to heatsinks, where the fan is parallel to the cpu (not tower heatsinks). I was always under the impression that the cpu fan should pull the hot air from the heatsink, and push it into the case, allowing the case fans to exhaust the hot air. However, last night, while I was working on a friend's computer, I noticed that the cpu fan was setup so that the fan pulled air from the case, and pushed it towards the heatsink. I started googling around, and noticed that this approach was a common suggestion on various forums, and now I'm wondering which is the better method. So here are my questions:

1) What is the preferred method direction for airflow?

2) Is the direction of airflow contingent upon the type of heatsink that is used? (traditional, where it's heatsink -> fins -> fan, or heatpipe, where it's heatsink -> heatpipe -> fins -> fan)

3) Is their a significant difference in CPU temp if the fan is pushing or pulling?

-Rob

[DIREWOLF75]

1) What is the preferred method direction for airflow?

Depends on the case and HSF too much to say for certain.

Most cases have a general airflow from the front to the back, sometimes also from the side or towards the top or bottom, so that´s what you have to fit the cpu HSF into, preferably causing as little disturbances or unmoving hotspots as possible.

With a classic HS, it´s usually simple, the fan should just blow at the HS, and if you have a side duct providing it with cooler air from outside the case, so much the better.
With a HS where the fan is on the side or above/below, it should generally be mounted to push air upwards or backwards relative to the case.

2) Is the direction of airflow contingent upon the type of heatsink that is used?

Yes. Nowadays, most that have optional ways to mount the fan will include instructions on what mounting is preferable, some also show what is ok and what mounting direction should not be used.

3) Is their a significant difference in CPU temp if the fan is pushing or pulling?

With any sort of HSF where the air isn´t restricted in where it flows, having the fan pushing air at it is nearly always much better. If the HS itself uses ducting, a sucking fan can sometimes work as well, and very rarely, better than a pushing one.

[rdege]

Thanks for the reply. I went home and checked out a stock intel HSF (from a 2012 core i3), and an AMD HSF (from a 2007 Athlon64), and both pushed air back onto the heatsink. I was shocked! I don't know why, for so many years, I was under the impression that pulling the hot air from the heatsink was the best method.

[Sauron_Daz]

Its just a counterflow system, like in many heat exchangers.

[Hammer_Time]

( sorry, couldn't resist, will go back to standing in the corner now... )

[DIREWOLF75]

( sorry, couldn't resist, will go back to standing in the corner now... )

That´s actually not such a bad depiction of how my friends old K6-2 system looked for a while when the usual cooling had broken and he hadn´t found the right way to fix it yet.

[Sauron_Daz]

( sorry, couldn't resist, will go back to standing in the corner now... )