My Jeep has both front seats heated, with both a "HIGH" and a "LOW" setting. As well as steering wheel heat. I can't believe how fast the wheel gets hot. Granted we don't get very cold weather here, but within 3 or 4 minutes I have to turn it off. And the wheel is very thick and large in diameter, and is wrapped with leather.
I can't imagine how many amps it's drawing when all that crap is up and running. Not to mention the rear window defroster, along with the fan blowing on it's highest setting. (It has like 6 speeds), and sounds like a J-79 on, "HIGH". I don't know what the alternator puts out, but it has to be A LOT.