Should You Use External or Internal Air Circulation for Air Conditioning in Winter?

[McEzra]

Winter air conditioning should use external air circulation. The choice between external and internal air circulation when driving with the air conditioning on depends on the situation, as explained below: 1. External air circulation mode uses a fan to draw outside air into the car, meaning the air passage between the outside and inside of the car is open. The air blown by the fan comes from outside, and even if the fan is off, airflow is still drawn into the car while driving, replenishing fresh air inside. 2. Internal air circulation mode closes the airflow passage between the inside and outside of the car. Without the fan, there is no airflow circulation, and when the fan is on, the airflow drawn in comes only from inside the car, creating internal airflow circulation. Internal circulation mainly prevents external dust and harmful gases from entering the car effectively and also helps maintain warmth. 3. Internal circulation is mostly used in traffic jams, while external circulation is preferred on highways. The use of internal and external circulation should be combined with air conditioning and heating. External circulation allows you to breathe fresh air from outside. 4. Turning on the air conditioning is to lower the temperature inside the car, so external circulation should not be used at this time. You can occasionally switch to external circulation to let in some fresh air.

[Melissa]

It really depends on the situation. In winter, both internal and external air circulation have their advantages when using the car's heating system. If the car interior is freezing cold when I first get in, I'll turn on internal circulation for a few minutes to let the warm air circulate quickly and warm up faster. Once the temperature rises, I switch to external circulation to bring in fresh outside air. Otherwise, keeping it sealed for too long can easily cause the windshield to fog up, affecting visibility while driving and making breathing uncomfortable. Especially when stuck in traffic behind trucks, the exhaust fumes can give you a headache - internal circulation helps block those odors. On highways, I mostly use external circulation for ventilation since the high speed keeps dust from blowing in anyway. The key is not to stick to just one mode all the time.

[ChloeAnn]

The most frustrating thing about using the heater is window fogging. I learned this the hard way during a long drive when foggy windows made it nearly impossible to see the road. Through trial and error, I figured out the solution: using recirculation mode for quick warm-up when starting the car, but switching to fresh air mode after about 15 minutes to dehumidify and expel interior moisture. I once tried directing warm air at the windshield, but ended up with freezing feet and mediocre results. Now I've developed a habit of running fresh air mode for 3-5 minutes before switching - the cabin air becomes noticeably fresher. During rainy days or with multiple passengers exhaling moisture, I maintain fresh air mode throughout the trip to ensure clear visibility.

[MacRose]

In winter, I mainly consider two things when using the air conditioning: fuel efficiency and peace of mind. For short trips, using the recirculation mode is definitely the way to go—it heats up the cabin quickly and doesn’t consume extra fuel. However, for drives longer than half an hour, you need to be cautious. Recirculation can lead to higher carbon dioxide levels, making you drowsy, and safety comes first. I specifically bought a car air purifier with PM2.5 filtration to use with the fresh air mode. Snowy days are the most troublesome—if you use fresh air mode and snowflakes get sucked in, the air filter can freeze, and repairs can cost hundreds. So, I only use fresh air mode for extended periods in dry weather, and in snowy or rainy conditions, I rely on recirculation along with the defogging function.

[VanColeman]

Last week, while stuck in traffic taking the kids to school, I noticed a phenomenon: when the air recirculation was on, the backseat passengers kept complaining about feeling stuffy, but switching to fresh air mode perked everyone up. Later, I looked it up and learned that oxygen levels can drop in an enclosed space. Now my routine is: turn on recirculation for three minutes after a cold start to warm up, then immediately switch to fresh air mode for ventilation once the temperature stabilizes. It's especially important to ensure good airflow when elderly or children are in the car - even cracking a window slightly helps more than keeping it completely sealed. However, during severe smog, I have to compromise and use recirculation since health comes first. The cabin air filter needs monthly checks too - if it's clogged, fresh air mode won't work properly.

[DelLilah]

As a northerner, I've long figured out how to deal with foggy car windows in winter. The key is controlling temperature differences: turning on the external air circulation brings warm air from the engine compartment into the cabin, acting as free heating. But in extreme cold below -20°C, switching to internal circulation is necessary to retain warmth. My go-to method is turning on the rearview mirror heating function while using the air conditioning, which works best with external circulation for dehumidification. Another trick is using AUTO mode to let the system automatically switch between circulation modes—much more convenient than manual adjustments. On highways, directing the air vents toward the windows prevents fogging every time.