Does using multiple monitors cause the iMac to run hotter? I have noticed my iMac (Retina 4K, 21.5-inch, Late 2015) tends to run hot &amp; noisy when watching some simple videos. I have tried whatever light duty diagnostics I can manage, such as activity monitor and the built in diagnostic tool, but nothing seems to be apparent.
The only thing I can think of is that my iMac is connected to two external monitors: one is a semi-retired older iMac in target display mode, and the other is a Phillips monitor.
Is it possible that supporting external monitors causes the iMac to run hotter?
It could...  I would suggest getting a can of compressed air and blowing out the fans.  If you haven't done this recently, it could be the cause of the extra heat.  When blowing out the fans DO NOT LET THE FANS SPIN!!!  I have killed a laptop while doing that so be very careful when blowing out the fans.