Should the Car's Heating System Use Internal or External Air Circulation?
2 Answers
It is recommended to alternate between internal and external air circulation when using the car's heating system to maintain better air quality inside the vehicle. Here are the relevant details: 1. The function of external circulation is to connect the air inside and outside the car, thereby replenishing fresh air. When external circulation is turned on, the air inside and outside the car is connected. As the vehicle moves, airflow will automatically draw outside air into the car due to wind pressure. 2. Internal circulation closes the airflow passage between the inside and outside of the car, and the blower circulates the air inside the cabin. Since the oxygen level inside the car is limited, it is generally advisable to use external circulation to maintain airflow between the inside and outside of the car. However, in certain special situations, internal circulation must be used, as failing to do so could pose fatal risks.
I've been driving in the north for over a decade and have extensive experience with winter heating. When you first start the car and the engine coolant hasn't warmed up yet, turning on recirculation mode can quickly warm up the cabin by repeatedly heating the same air. But once the temperature rises, it's better to switch to fresh air mode to let in outside air—otherwise, the windows tend to fog up, and the air gets stuffy. During traffic jams or smoggy days, I always use recirculation to prevent exhaust fumes from entering. It's the same principle as home air conditioning: after heating and insulation, proper ventilation is still necessary. The key is to monitor window fogging and physical comfort—switch to fresh air immediately if fog appears, and use fresh air mode in good weather to maintain airflow. Flexibly alternating between these two modes keeps you both warm and safe.
