iMac Fan runs fast and hard Is it common for an imac fan to kick into full swing when booting up and never idling down even after 10 minutes? It sounds like a vacuum.

Would going in to the BIOS(no idea how to do that on a mac) and resetting help solve the problem.
Not normal. I had the same problem with an iMac a few years back and had to have the logic board replaced (under warranty thankfully).

You might have a SMC (System Management Controller) problem. This article explains how to reset it: 
http://support.apple.com/kb/HT3964?viewlocale=en_US&amp;locale=en_US

You might also look at a tool like iStat Menus:
http://bjango.com/mac/istatmenus/

What I found with iStat was that my CPU was running extra hot, hence the extra fan speed.

I did end up using an app called SMC Fan Control to mitigate the problem before getting the logic board replaced.