Some systems may reach high temperatures and overheating conditions while running StarCraft II. This is mainly due to the video card rendering the screens at full speed. As a workaround, there are two lines that you can add to your Documents\StarCraft II Beta\vari ables .txt file to limit this behavior.
Frameratecapglue=30
Frameratecap=60
The frameratecapglue controls the framerate at the menu screens. The frameratecap controls the framerate on all other screens. You may adjust these numbers to your liking.