Does turning on the AC while using the heater consume more fuel?
2 Answers
Using the car heater with the AC turned off does not consume additional fuel. Function of the heater: The warm air comes from the heat generated by the engine during operation: When the engine's cooling system dissipates heat from the engine, the dissipated heat is blown into the car by a fan to form warm air; when the warm air is not in use, the fan stops running, and the warm air outlet closes, allowing the dissipated heat to be completely released into the atmosphere. Therefore, the warm air from the car is a form of waste heat recovery and does not consume gasoline. Function of the AC: Cold air is formed by pressurizing the refrigerant through the compressor, causing it to liquefy and then vaporize, absorbing a large amount of heat from the air; when the cold air is turned on, the compressor pulley drives the compressor to work, increasing the engine load and consuming a certain amount of fuel.
I specifically tested this on a long-distance drive last time. The heater itself doesn’t actually consume fuel! It uses the heat dissipated by the engine, which is essentially waste heat utilization—turning on the heater is like opening a valve for hot water pipes. However, if you have the AC button on, the compressor will activate, and that thing does consume fuel. Especially when starting the car in winter, the engine temperature is low, and the AC will force the compressor to work to quickly defog the windshield, which leads to higher fuel consumption during this period. But after defogging, turning off the AC and simply using the heater to blow on the windshield can also prevent fogging. A pro tip for saving fuel is: wait until the coolant temperature gauge reaches the midpoint before turning on the heater, and keep the AC button off for maximum fuel efficiency. For electric vehicles, the heater is indeed a power hog, as the principle is different.
