Advice on Push/Pull Radiator Config Using Mismatched Fans

I've started a new higher end gaming build and have decided to try an AIO for the first time.

The AIO is the NZXT Kraken X62 that comes with 2 NZXT 140mm fans, and the case is a Fractal Design Define S2. The case comes with 3 x 140 fans (Fractal Design Dynamic X2 GP-14) - 1 rear exhaust and 2 intakes in the front. Originally I was going to mount the radiator on the top, but thinking a front mount might be more efficient getting fresh cool air straight to the radiator.

Rather than throw the existing case fans in a draw I'm thinking I might as well pair them with the NZXT fans for a push pull config, with the case fans doing the pushing and the NZXT fans doing the pulling.

I know it's not optimal to have mismatched fans but the interwebs seems to say it's general OK as long as you have your more powerful fans doing the pulling, The potential problem however is the case fans are a 3 pin 1000rpm and the Kraken fans are 4 pin PWM 500-1500 RPM, so when not under load the case fans will be spinning faster but under load the Kraken fans should kick in.

Is there any potential major problem with this set up, matching PWM and non-PWM fans on a radiator, particularly when not under load? If it's not going to bring any additional benefit, make too much noise or worse cause damage to the fans then I may as well just not include the case fans, but I'd hate to see them go unused.

Comments

  • high static pressure fans in push, low static pressure fans in pull

  • No major problem with the setup. There will be a benefit coming from push pull. Even better still, you can stop the kraken fans when not under load as the case fans will provide enough air flow over the radiator.

    One thing to consider would be that you'll be blowing warm air past the radiator into the case, potentially heating up the GPU.

    You could switch the fans around so that the kraken fans are pushing and the case fans pulling out and exhausting. You'll have to move the filters to the intake fans.

    Or keep the radiator as a top mount in push-pull if they'll fit as hot air from the GPU rises.

  • Here's some basic thermodynamics principles I've discovered over the years:

    • It's better to have positive case pressure than negative. That means any leaks though case seams etc will tend to blow dust away rather than suck it up
    • Cold items first in the flow, hot last. Same as a car radiator (or any other heat exchanger coil) - you want to keep a linear temperature gradient from the start to the end of the airflow section. That is - don't suck air straight onto your CPU, as it'll then blow over everything else on the way out and thus keep everything hot.
    • Even if you pump 10x the amount of air through, if your CPU or GPU cooler isn't adequately directing the heat up the fins, then more air won't really help. Obviously your AIO is going to be ideal compared to an air cooler.

    Finally:
    - It's only air… You're not dealing with space-grade tolerances or harsh conditions that are life threatening. Have a play around and see what works for your setup! You can always relocate everything so you've got nothing to lose by trying different layouts.

    • Cold items first in the flow, hot last

      There's only two things that matter: GPU and CPU and placing things in front of them restricts airflow …

      Obviously your AIO is going to be ideal compared to an air cooler.

      Not really if it's a large case. Custom loop is better.

  • Pretty sure those are the same fans I have and don't bother using them with radiator, just adds noise.

    They're only good for non-restricted airflow through case and nothing special at that. There's two types of fans: airflow and static pressure and you need good static pressure to force air through radiator or heatsink fins.

    There are a few fans that do both good airflow with high static pressure AND they're quiet, such as some Noctua fans but do not take marketing's word for it.

    I recommend avoiding AIO coolers though because the Noctua DH-15, provided you can fit it in your case, is 2 degrees off the Kraken X62 for performance (which is pretty much the best AIO cooler). And no AIO has better noise vs performance than the DH-15. And it's usual price is $120.

    Also CAM is just … why did NZXT do that? Make great hardware and then make CAM …

    Anyway as far as radiator placement obviously getting heat out is best but it only affects temps by 5 or six degress (without a GPU) having CPU radiator at the front intake.

  • I did originally think of having the radiator on top, but that means i'm getting hot air from the GPU coming up through the radiator. In the end it's one of the other , cool air to GPU first or CPU first, and the other will get warmer air.

    The push/pull in the front was also to generate positive pressure, with the just the single exhaust in the back. I do agree on the suggestion that it might be better to keep the temperature increase linear, in which case it would make sense to have the radiator up top. To keep positive pressure I'll pick up an extra fan for the intake and have 3x 140mm fans bringing air in. 2 of the 3x 140mm fans exhausting will be pushing through the radiator so should see enough resistance that good positive pressure is maintained.

    Re custom loop yes that would be ideal, but a little cost prohibitive right now - maybe next build.

    Re Noctua DH-15 - did consider this, and actually agree this is technically a more efficient option for noise vs performance but I've done a few air cooled builds already and to be honest just want to try something new for the experience and fun hence going with AIO.

  • Well this video was quite insightful. (Results at 12:08 - just hit pause there)

    Interesting the GPU has minimal impact from a front radiator, while CPU was up almost 10 degrees higher when radiator is on top with am open GPU. Blower style GPU put less temp on the CPU, but the CPU still runs a bit hotter.

  • I would mount the X62 up top & use the fans that came with it
    Leave the other 3 fans where they are, that would be the ideal set up
    Don't do push pull, you won't get that much extra out of it

    When you pull all your hair out trying to get the X62 software working, I hope you did not just buy it for the lights, you can use Core Temp to monitor your X62. Or send back the X62, like I did, and get a be Quiet! CPU cooler & use Core Temp with it; my drinking has gone done since I got rid of the X62. It is a nice cooler but is let down by the software

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