The MacBook Pro 16" has a problem.

If you connect certain GPU models (specifically the 5300M/5500M) to external monitors with certain resolutions, many users report that their MacBook gets really hot and the fans spin up really loudly.

It is documented in this nearly 200 page MacRumors thread: https://forums.macrumors.com/threads/16-is-hot-noisy-with-an-external-monitor.2211747/

And this Hacker News thread: https://news.ycombinator.com/item?id=22265235

Specifically, many users report extremely loud fans when connected to 2560x1440p60 monitors.

The solution to this problem, however, is easy.

Before, when connected to a 1440p monitor, my MacBook Pro 16 inch reports 18–20W of power draw from the GPU (Radeon High Side).

It doesn’t take long for all this extra power to heat up the laptop and cause the fans to spin up, even if the MacBook is idle with nothing else running!

But if you force enable HiDPI mode for your external monitor, this is what happens:

What exactly is HiDPI mode? Well, it’s basically forcing macOS to internally render at 2x resolution. So in the case of a 2560x1440p monitor, macOS is internally rendering at 5120x2880p. You can tell, since the screenshot of the power draw monitoring utility (iStat Menus) is twice as sharp in the second example.

Now the MacBook is drawing a much more reasonable 5–6W and stays silent during normal operation, as it should! Now it feels like a Pro machine!

Seeing as how it makes no sense that rendering at 2x resolution cause 1/3 of the power draw, this is most likely a GPU driver bug on Apple or AMD’s end, and a temporary solution could be force enabling HiDPI mode for 1440p monitors in the next release of macOS Big Sur.

Note, these power draw settings only work if you keep the MacBook lid closed.

You can force enable HiDPI mode yourself by following the instructions in this GitHub repo: https://github.com/xzhih/one-key-hidpi

When using this script, make sure the MacBook lid is closed.

My script run looked like

% bash -c "$(curl -fsSL https://raw.githubusercontent.com/xzhih/one-key-hidpi/master/hidpi.sh)"

_    _   _____   _____    _____    _____ 
 | |  | | |_   _| |  __ \  |  __ \  |_   _|
 | |__| |   | |   | |  | | | |__) |   | |  
 |  __  |   | |   | |  | | |  ___/    | |  
 | |  | |  _| |_  | |__| | | |       _| |_ 
 |_|  |_| |_____| |_____/  |_|      |_____|

============================================

(1) Enable HIDPI
(2) Enable HIDPI (with EDID)
(3) Disable HIDPI

Enter your choice [1~3]: 1

-------------------------------------
|********** Display Icon ***********|
-------------------------------------

(1) iMac
(2) MacBook
(3) MacBook Pro
(4) LG Display
(5) Pro Display XDR
(6) Do not change

Enter your choice [1~6]: 3

------------------------------------------
|********** resolution config ***********|
------------------------------------------
(1) 1920x1080 Display
(2) 1920x1080 Display (use 1424x802, fix underscaled after sleep)
(3) 1920x1200 Display
(4) 2560x1440 Display
(5) 3000x2000 Display
(6) Manual input resolution

Enter your choice: 4
Enabled, please reboot.
Rebooting the logo for the first time will become huge, then it will not be

Please note, your MacBook fans may be loud on the initial restart, but will quickly settle down and be silent on every subsequent restart. And once again, this fix only works when the MacBook lid is closed.

So welcome to having a silent MacBook when plugged into a monitor now! As it should be!

Interestingly enough, setting the scaled resolution to 1080p also seems to have a similar result, but 1080p on a 1440p monitor looks terrible.

Found this article helpful? Feel free to buy me a coffee :)