The heat comes from the coolant.

When engine works, it generate a lot of heat. 60-70% of the energy is wasted on generating useless heat. The coolant carries the heat away from the engine block and exchange with the atmosphere. When you turn on the heater, part of the coolant is directed to a heating core and the heat (which was going to send to the atmosphere) got sent to you.
So, to answer your question, no, you are not using extra energy by turning on the heater.

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• 回複：Thank you very much -tellUlater- ♂ (0 bytes) () 01/23/2009 postreply 00:54:03