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I am thinking of purchasing another Mac mini - I already have an older one - and I am planning to keep them on top of each other as I have limited space on my desk.

I was wondering if it is safe? I am concerned about ventilation. If this is not a good practice then is there any solution that would allow me to keep my new Mac minis on top of each other on my desk?

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    I wouldn't put them exactly on top of each other, but if you have some rubber post (or anything non-conductive), which you could place between the macs on each corner, you should be good to go. – X_841 Jan 22 at 12:20
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    It's not clear from the question, but are you planning on using them both at the same time? – Mast Jan 23 at 22:00
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    Yes, one would be a work machine and the other is just for hosting Plex server and serving my Apple TV – gyurisc Jan 24 at 6:10
  • @X_841 Why would something conductive be a problem? – Oskar Skog Jan 25 at 19:40
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In How to position your Mac mini, Apple, perhaps being overcautious, say not to:

Don't put anything on top of your Mac mini or stack Mac minis on top of each other either. If your Mac mini is configured with AirPort or Bluetooth, you could hamper the signal strength since the antennas are located in the top of the computer.

If you only connect with Ethernet the connectivity issues are moot and even if you do use a Bluetooth keyboard or Wi-Fi you may well find it it works well enough for your situation.

Although not mentioned in the support article the Mac mini dissipates a large amount of heat through the case and insufficient ventilation will cause an increased temperature particularly in the lower mini if the hot air is trapped and can not escape.

It will certainly not harm anything to test stacking them as they will shut down if they get dangerously hot. Prior to a temperature related shutdown however you may find reduced CPU performance as there is less thermal head-room to Turbo the CPU clock, and it may also possibly shorten the lifetime of components due to running near the upper end of their safe temperature range for extended periods.

So while it can't hurt to try you should watch the temperatures. As @IconDemon mentions in their answer with sufficient ventilation this will not be an issue. As they mentioned in their answer ventilation may be improved by putting rubber feet or other spacers to increase the size of the air gap between them.

If you try it and find it is causing a problem either with heat (and thus fan noise) or connectivity, you could perhaps put them both on their sides with a gap between. As mentioned in the support doc above and in this question Is it safe to run a Mac Mini (i5) on its side? you can safely do this.

This vertical configuration would allow air heated by the cases to easily rise and escape rather than be trapped under the mini above.

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    It will not harm to try as they will eventually shut down if they get too hot. Reduced CPU performance will happen before that because of less thermal head-room to Turbo the CPU clock, and also possibly shortening the lifetime of components from running near the upper end of their safe temperature range for extended periods. So it can hurt to try, in more subtle ways than just shutdown from thermal emergency! – Peter Cordes Jan 22 at 23:46
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    The statement you quoted says nothing about thermal issues. Instead it says that putting things (presumably metal things) on top of the mac mini will interfere with Wifi and Bluetooth. So instead of placing them on the side (which would still interfere with Wifi and Bluetooth) the correct solution would probably be that it's OK to stack them on top of each other if you use wired networking and don't use bluetooth – slebetman Jan 23 at 4:08
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    @PeterCordes & slebetman I've updated answer based on your comments. – lx07 Jan 23 at 11:28
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    If you do have thermal issues, you could simply try putting some spacers in between. – user253751 Jan 23 at 11:43
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    @user253751 - yes as mentioned in other answers this is probably so - I'll update answer to include it. My main point here (small though it is) is that if you test stacking them horizontally and have an issue then putting them vertically is another option. – lx07 Jan 23 at 11:52
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I use an IKEA 7-inch trivet underneath my Mac mini to improve ventilation. That might help between stacked Mac minis :

IKEA LÄMPLIG Pot stand

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    Something like this would be better if it weren't made of metal. – user1751825 Jan 24 at 0:25
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    This is an awesome idea. We just need to keep looking for something non-metalic – gyurisc Jan 24 at 6:17
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    @user1751825 Why is metal bad? It's perfect to conduct heat away. The Mini's plastic base is in contact anyway, and the trivet has plastic feet, if you were to stack them, so there's no scratch risk. – benwiggy Jan 24 at 14:34
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    I would imagine that metal could interfere with the wireless radio transmission. I could be wrong though. – user1751825 Jan 26 at 18:38
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    Ah. Perhaps several stacked together might. I'll do some tests with and eithout, ans see if there's a difference. (I use Ethernet.) – benwiggy Jan 26 at 21:17
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I wish I had a picture for absolute proof, but at one point we stacked up 5 Mac minis for several years running two FirstClass email servers, an OD server, and two file servers. They were in a well air-conditioned systems room with superlative ventilation.

To improve the air-flow between the Mac minis, I did stick 1/2" rubber feet at each corner of the chassis.

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    I had four mac minis stacked up as testing devices at work until I got a parallels license and virtualized my testing environment. Didn't encounter any issues with them stacked as well. Just to corroborate Icon's answer. I didn't even bother spacing them out but if you're using them for more than testing definitely a good idea. – Robby1212 Jan 23 at 17:06
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It depends on the workloads you subject it to. Except for extreme scenarios, you should be fine. Create a little clearance between the units and allow room for convection, don't put them in a cupboard.

If you are building a render farm out of new Mac mini's (don't), you're probably using them in a professional capacity. And you're probably planning to phase them out after 3-5 years. These are the kinds of scenarios where heat may be problematic.

If you plan to regularly max out the CPU and/or GPU of the unit (rendering, transcoding, gaming, heavy server loads), then two effects come into play:

  1. Thermal Throttling: Suboptimal performance, the CPU reduces its clock speed if it gets hotter.

The degree to which occurs depends on the design of the Mac mini's cooling solution. Some reviews indicate that the current model throttles during benchmarks and highly CPU-intensive workloads. Others indicate that it's not much of an issue.

  1. Reduced Lifespan: A Mac mini may die a little sooner if it is running hot continuously.

As stated by @lx07, the Mac mini will shut down if it gets too hot. However, this thermal protection only prevents the computer from burning out. Well before that point, the increase in temperature is likely to reduce both lifespan and reliability of electrical components.

Apple designs the thermal solution accordingly and buys sufficiently high-quality components that this should not generally be an issue. The fan in a MacBook Pro often does not kick in before it reaches 70c/158f. This is deliberate.

Do note that HDDs are more susceptible to heat. HDDs produce more heat than SSDs and are (in theory) more severely affected than other components because they rely on specific mechanical tolerances. BackBlaze keeps their drives very cool: mostly below 30c/86f. I'd expect the effect to be exacerbated above 50c/122f, but I can't find a good source. Drops and vibration are likely bigger contributors to HDD failure.

  • I would do any drastic with them really. One is just a work machine and the other would be just running different servers like Plex. One would be mainly used in work hours and the other is in the evening :) – gyurisc Jan 24 at 6:15
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Lots of great answers already but I have recently tried this and while heating etc., were not a problem, bluetooth connectivity was. It is hard to imagine not using bluetooth for something so be aware that covering the mini with something metallic and hence shielding can cause problems. I reshuffled my stack with the mini on top of two hard drives, with an Apple CD/DVD reader on the very top (Apple requires these drives to be connected directly to the computer). As long as I position the Apple CD/DVD reader just so, I get good bluetooth again. (-:

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