IMac – Does using multiple monitors cause the iMac to run hotter

This is an excerpt of Appple's Application Kit Release Note for Lion regarding fills screen apps & multiple desktops.

Multiple Monitors and Full Screen (New since early 2011 seed)

We have made some simplifying assumptions for Lion Full Screen behavior on multiple monitors. Multiple monitors are treated as a single unit by Spaces, and therefore are also treated as a single unit in Full Screen. This means that all monitors will be dedicated to windows belonging to the full screen application, and there can be only one primary full screen window visible at a time. A secondary monitor is useful for inspector windows.

Secondly, because the menu bar is located on the main monitor, the primary full screen window will be located on the main monitor as well. This allows the menu bar, floating toolbar, and full screen window to maintain their interrelationship on the same monitor.

full document can be found here: http://developer.apple.com/library/mac/#releasenotes/Cocoa/AppKit.html

According to this document it isn't possible.

Well, yes, driving two monitors requires more work from a GPU. But is 80 C normal, long-term-wise? I think not. You can get yourself badly burned at 80 deg, so why would this be good for a computer part, especially over 2 or 3 years? :-/

I remember I had a problem with a Mac Pro years ago. All the RAM slots were occupied, and iStat reported 70+ temperatures in these slots, even though the fans were doing their job. But I had a lot of crashes and kernel panics. Then I thought that such temperatures could not be helping. Then I installed a little helper app that enables you to set the minimum speed for any fan in you system. I just set the fans to 1200 rpms instead of the default 800, and everything began behaving smoothly from that point. Putting my hand to the back of the computer I could really feel the difference in temperature. And the modules' temperature went from 70-80 C to 35-45 C in about 5-10 minutes!!

Of course the fan noises was slightly more annoying, but I was willing to sacrifice a bit of my sanity for a stable computer. :-)

The app was named smcFanControl (http://www.eidac.de/). Works with Lion as of v 2.3. And free. There are of course other apps that would do the same, but this one has worked flawlessly for many years.

I think that Apple is setting it's temperature threshold limits a little too low, all for the sake of silence of operation...