Is it better to use internal or external air circulation for heating?

[GarrettFitz]

First turn on the internal circulation for heating until the car temperature rises, then switch to external circulation. Below are the specific introductions to internal and external air circulation in cars: 1. External circulation: External circulation refers to drawing air from outside the car, directing it to the air conditioning system for heating or cooling, and then blowing it out from the vents. External circulation essentially supplements fresh air to improve the air quality inside the car. It should be used for defrosting in winter or defogging in summer, as the air drawn from outside contains higher oxygen levels and is drier, making it more effective for defrosting or defogging. 2. Internal circulation: Internal circulation draws air from inside the car, creating an airflow cycle within the vehicle. The main function of internal circulation is to promptly and effectively prevent external dust and harmful gases from entering the car. It heats up the car faster in winter and cools it down quicker when the air conditioning is on in summer. It can also be used during smoggy days. Internal circulation cycles the air inside the car, helping to maintain the interior temperature more effectively.