# CPU fan airflow direction?

**URL:** <https://boards.straightdope.com/t/cpu-fan-airflow-direction/249010>\
**Category:** Factual Questions\
**Created:** [June 6, 2004, 11:54pm UTC](https://boards.straightdope.com/t/cpu-fan-airflow-direction/249010 "2004-06-06T23:54:09Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![rabbit](https://avatars.discourse-cdn.com/v4/letter/r/919ad9/32.png) [@rabbit](https://boards.straightdope.com/u/rabbit)\
**Post date:** [June 6, 2004, 11:54pm UTC](https://boards.straightdope.com/t/cpu-fan-airflow-direction/249010/1 "2004-06-06T23:54:09Z")

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Is it better for the CPU fan to blow down onto the heat sink or to pull air through the heat sink? (That is, the fan blows away from the metal drawing air through the vents to do so).  
Specifically curious regarding the coolmaster type fans on older (P3) intels. (wasn’t paying attention when I pulled off the damn thing to clean it as to which way it was facing… :smack: )

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**Author:** ![Harmonix](https://avatars.discourse-cdn.com/v4/letter/h/3ec8ea/32.png) [@Harmonix](https://boards.straightdope.com/u/Harmonix)\
**Post date:** [June 7, 2004, 12:40am UTC](https://boards.straightdope.com/t/cpu-fan-airflow-direction/249010/2 "2004-06-07T00:40:42Z")

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Do an empirical test and check the temperatures both ways.

I do however believe most fans except for a few designed by alpha blew down into the heatsink.

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**Author:** ![iwakura43](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@iwakura43](https://boards.straightdope.com/u/iwakura43)\
**Post date:** [June 7, 2004, 12:44am UTC](https://boards.straightdope.com/t/cpu-fan-airflow-direction/249010/3 "2004-06-07T00:44:29Z")

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99% of the time, the fan should be blowing air **on** to the heatsink; the air should be blowing out the sides of the heatsink.

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**Author:** ![Toddly](https://avatars.discourse-cdn.com/v4/letter/t/22d042/32.png) [@Toddly](https://boards.straightdope.com/u/Toddly)\
**Post date:** [June 7, 2004, 3:27am UTC](https://boards.straightdope.com/t/cpu-fan-airflow-direction/249010/4 "2004-06-07T03:27:17Z")

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Yes, direct it to blow downward and all is cool. 🙂

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**Author:** ![rabbit](https://avatars.discourse-cdn.com/v4/letter/r/919ad9/32.png) [@rabbit](https://boards.straightdope.com/u/rabbit)\
**Post date:** [June 7, 2004, 2:37pm UTC](https://boards.straightdope.com/t/cpu-fan-airflow-direction/249010/5 "2004-06-07T14:37:25Z")

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thanks! Thought so, but just wasnt sure.