Is it better to use internal or external air circulation for heating?
3 Answers
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.
When using the heater personally, I find both the recirculation and fresh air modes have their own advantages, depending on the situation. After a cold start in winter, the recirculation mode can quickly heat up the air inside the car, warming up faster and making it more comfortable. However, if left on for too long, the air can become stuffy, and the windows tend to fog up, affecting visibility—I’ve encountered this several times where it almost became hard to see the road. So, I usually start with recirculation for a few minutes to raise the temperature, then switch to fresh air mode to introduce outside air, which helps prevent fogging and keeps the air fresh. On highways or in heavily polluted areas, I prefer using fresh air mode more often to avoid inhaling exhaust fumes, but in suburban areas with good air quality, I’m more flexible. In short, there’s no absolute good or bad—it’s about adjusting flexibly based on actual needs.
Regarding the heating circulation system, I believe the external circulation mode is more reliable, especially in terms of safety. The confined interior space can accumulate moisture during prolonged internal circulation, leading to windshield fogging - a serious issue that could potentially cause accidents. I've personally experienced dangerously reduced visibility from heavy fogging while using internal circulation during rainy conditions. Since then, I've disciplined myself to use external circulation more frequently, as the better airflow quickly eliminates fog. Admittedly, internal circulation does warm up the cabin faster in cold weather and improves fuel efficiency slightly, but one shouldn't prioritize warmth over safety. When encountering poor external air quality (like dusty traffic jams), briefly switching back to internal circulation is acceptable, but avoid prolonged use. Developing a habit of regularly alternating between modes to maintain proper ventilation is the wisest approach.
