Your car's engine is a heat engine; it converts the thermal energy from burning fuel into energy to move your car and power its
systems. On a cold winter day, you needn't feel guilty about cranking up the heat in your car; running the heater doesn't cost any additional energy beyond the small amount needed to run the fan. Explain why this is so.
The efficiency of the heat engine is less than 100%. The heat engine converts the thermal energy from the burning of fuel to the mechanival energy. Thus, some of the energy gets lost as waste heat.
Hence, this waste heat is used up to heat up the interior of the car and person feels warmer in the car.
Thus, the waste heat generated in the engine is used for the heating of the car interior.
