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Thread: Which way up to mount this PSU?

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    Which way up to mount this PSU?

    Every system I've built in the past has had the PSU at the top of the case so the PSU fan has blown down into the system.

    My latest case has the PSU mount at the bottom of the case with a grill on the base, however the PSU can be mounted facing up or down. At the moment I've mounted it upside down so that fan blows upwards into the system but which is the better orientation?

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    Re: Which way up to mount this PSU?

    The larger (e.g. 120mm) fan in the PSU is an intake fan, not an exhaust fan - PSUs usually exhaust hot air out of the back of the PSU, rather than take external cool air and blow it through the PSU into the case.

    Assuming that your new case has a cutout/mesh on the bottom of the case where the PSU is mounted, you have two options:

    1. PSU fan facing up (sucks air from case, through the PSU, and out the back)
    2. PSU fan facing down (sucks air from outside, through PSU, and out the back)

    Option 1 uses the PSU intake fan to contribute more to the overall cooling of the case - however, it does mean that the PSU will be using hotter air from inside the case to cool itself, which in extreme cases might mean the PSU runs with less thermal efficiency, so it may draw a little more power from the wall outlet, or it may have to run its own cooling fans at higher speeds to compensate.

    Option 2 isolates the PSU cooling and airflow from the rest of the case, as it uses cool air directly from outside.

    If your case does not have a cutout/vent at the bottom where the PSU is mounted, you will need to install it with the fan facing upwards.

    What case and PSU do you have, and what's the overall airflow in your case like (e.g. how many intake and exhaust fans, and where are they located?

    Overall it's probably best to go for option 2 as long as your case has a cutout where the PSU is mounted.

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    zaphox (06-01-2012)

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    Re: Which way up to mount this PSU?

    timread has summed it up very clearly

    PSU fans don't blow air into the system they draw it out.

    The difference in air temperature in most lower mounter psu cases isn't that big as the two main sources of heat inside a pc are the graphics card and cpu which are both above the psu in a lower psu case so the majority of the heat will get vented out off the back and top of the case.
    Although it will depend on the case and graphics card as you can get a hot spot forming below the graphics card.

    Another question to ask is does your case have a filter on the vent in the bottom below the psu?

    Another question to ask is how long are the psu cables? Mounting the psu with the fan up tends to put the cables on the left side which means you need a couple of extra inches in length.

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    zaphox (06-01-2012)

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    Re: Which way up to mount this PSU?

    Thanks for those comments - very helpful.

    I can't remember if the lower vent has a filter or not, although I see where you're going with that - dust. I think if there is a filter fitted I will switch to having the fan intake air from underneath - otherwise I'll leave it as it since, as you pointed out, there wouldn't be much hot air at the bottom of the case.

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