What Your Car’s Air Recirculation Button Does—And Why You Should Be Using It

The many symbols on a car dashboard practically form a hieroglyphic language of their own—and thankfully, the air conditioning button, “A/C,” is one of the more self-evident ones. The same can’t be said for the air recirculation button, which is the button bearing a picture of a tiny car with a curved arrow inside it. But if you’re diving for the A/C button on a hot day, you shouldn’t ignore this lesser-known feature.

What Does the Air Recirculation Button Do?

The air recirculation button, as its name implies, recirculates the air already inside your car rather than pulling in the outside air. As Travel + Leisure reports, this is particularly useful when your air conditioning is on, because it’s way easier for the system to recirculate already cooled air than continually have to cool down new batches of hot air. Not only will this help your vehicle “get as cold as possible as quickly as possible,” as Eden Tyres and Servicing explains, but it’ll also allow the A/C to do its job using less energy—and that means you’ll burn through gas at a slower rate.

Depending on where you are, the outside air might have issues beyond its temperature. It could be full of pollution, exhaust fumes, or pollen and other allergens. Maybe you’re driving past a chicken farm or a wastewater treatment plant, and the outdoor air just really stinks. In short, the air recirculation button can help keep your car as cold, clean, and fuel-efficient as possible.

When Not to Use the Air Recirculation Button

If you’re cranking the heat during cold weather, on the other hand, you should usually skip the air recirculation button, as running the same moist air repeatedly through your vehicle is a recipe for foggy windows. Plus, the heating system warms up the air mostly using heat already generated by the engine, so it’s not guzzling gas in the same way the A/C does.

And it’s best not to use the recirculation button for a considerable length of time. Newer cars are increasingly sealed, so using the air recirculation button can increase the carbon dioxide levels in the car to uncomfortable levels fairly quickly. Some cars have CO2 sensors or the ability to open the recirculation door periodically, but neither is universal. Heejung Jung of UC Riverside’s Marlan and Rosemary Bourns College of Engineering suggests that if you’re going to use recirculation for more than a few minutes, you should increase the ventilation fan speed because, while sealed, air cabin systems aren’t airtight—so increasing fan speed gives a bit more ventilation.

[h/t Travel + Leisure]

This story has been updated with additional information about how long the air circulation button should be used.