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Thread: CPU heatsink fan - suck or blow?

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    Taz
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    CPU heatsink fan - suck or blow?

    I'm going to fit a 92mm fan onto my XP-90 heatsink shortly and I'm not sure whether there's a 'proper' orientation that should be used? Should the fan suck the hot air from the CPU and blow it out upwards or should it blow cooler air down into the CPU? Or doesn't it matter?

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    Real Ultimate Power! Grey M@a's Avatar
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    I have that sink and it's definately a blow orientation otherwise the heatpipes wot do their job

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    Taz
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    Quote Originally Posted by Grey M@a
    I have that sink and it's definately a blow orientation otherwise the heatpipes wot do their job
    Cheers, mate. The reason I asked what may have appeared to be a daft question is the following page from an excellent review:

    http://www.silentpcreview.com/article194-page2.html

    Quote: "Thermalright assures us that cooling is the same with the fan blowing up or down"

    I have two 120mm fans in my case and if I mounted the HS fan so that it sucked air then the hot air would enter the airstream of the two main case fans.

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    Now with added sobriety Rave's Avatar
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    Experiment then. Put it on blow, load up the processor with Prime95 and then take the temp after 15-20 minutes. Then set it to suck and do the same. Go with whatever works best. My money's on blow though.

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    Taz
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    You're right Rave (as usual!). If you look at the review (link in one of my posts above) - the third page of that review shows temperature readings with both orientations. The fan blowing down on the CPU produces slightly lower temperatures, which I guess makes sense.

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    Now with added sobriety Rave's Avatar
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    It still might be worth experimenting though since it'll take all of two minutes. You never know whether an airflow idiosyncracy in your case might swing the balance- it seems their testing is done on a bare testbench. Either way I suspect there won't be much in it.

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    noob question how do u change the fan
    from suck to blow?

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    Turn it upside down

    Unscrew it and make sure that the sticker side is facing down for a blow or for a suck sticker side up. The air always the way the sticker is facing!

    Chris

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    ..."It's Mega-Maid! She's gone from suck to blow!"...
    Classic Spaceballs line...

    S.

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    The problem with it sucking is that there's a negative pressure in the heatsink, and the middle of the heatsink gets about zero airflow. At least with it blowing there's some pressure there, and some airflow downwards towards the middle of the heatsink, although there's still a "deadzone" because of the fan's hub.
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    blow normally is best
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    Taz
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    Blow it is then! Thanks for all the advice.

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    HEXUS.timelord. Zak33's Avatar
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    *cough*

    subtle hint.....sometimes a fan works best if its held further from the heatsink...on little feet or spacers.

    The centre of a fan is all motor...the baldes are on the outside. There is a dead area in the centre....but at a short distance it swirls together.

    I have had 3 different heatsinks that worked better with the fan further away.

    I made thew feet with little bits of plastic....just glued them on....if they didnt work I snapped them off.

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    Some times with a 92mm heatsink you my want to think of funneling the air from a 120mm fan into the heatsink. That’s a great way to get more cooling for your buck, and get rid of any “deadzones” you may have otherwise. You can find a couple really great articles on the subject here.
    Tweak3D’s cooling guide
    Spode’s ducting/cooling guide
    (If I remember correctly they also has some info on why it may sometimes be better to err.. withdraw air than to.. expel air)

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    Senior Amoeba iranu's Avatar
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    Quote Originally Posted by Raggy
    Some times with a 92mm heatsink you my want to think of funneling the air from a 120mm fan into the heatsink. That’s a great way to get more cooling for your buck, and get rid of any “deadzones” you may have otherwise.
    I have a ducted 120mm fan at the rear of my case that sits right over the NB and cpu heatsink which was working as a normal rear case fan i.e. expelling hot air.

    CPU temps were @ 50°C on an overclocked 2500 @ 3200 speeds.

    I turned the fan around so it blows cold air onto the mobo and voila

    CPU temps are now 39°C idle, 43°C load.

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    Also by blowing down you get better airflow over your mofsets (if there close to ure CPU)
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