High-level heating uses more fuel.

We recently received a misconception that the car heater would need more petrol/diesel. As you look at the heater in the car not as the heating of a house can imagine is that not correct! The heating in the car works thanks to the waste heat from the engine. The engine block gets (very) warm while driving and has to be cooled by air. The hot air is either released directly into the environment or – if the heating is switched on – part of it into the passenger compartment. That’s why the heater doesn’t use a drop of petrol anymore. (Theoretically, however, the fan can use a little more electricity/fuel at high level)

The situation is different in the summer with the air conditioning! Their compressor is connected directly between the engine and alternator and, depending on the model, can draw a lot of power from the engine. (In the case of weak engines, you even notice a weak start when the air conditioning is switched on.) In contrast to heating, an air conditioning system therefore consumes additional fuel!