The “recirculate” feature in your car’s HVAC system helps retain clean, temperature-controlled cabin air. When recirculate is turned off, the car will only inhale outside air. When switched on, it tells the vehicle not to breathe outside air but to recycle the existing cabin air instead. Typically, the recirculate button is next to the AC on/off button. It looks like a car icon with a bold arrow curved around inside.

On or off, the vehicle takes air and heats it via byproduct engine warmth or cools it via the air conditioning system. Knowing when to use recirculate can help you maintain the ideal cabin temp and protect you from cruddy exterior pollutants.

When it’s really hot outside

In high temperatures, recirculating prevents your car from bringing in really warm outside air and working extra hard to repeatedly cool it. Overall, it helps the AC system easily maintain optimal cabin air temperature on hot days.

An exception to this rule of thumb is If your car is parked in hot weather and the cabin feels like an inferno when you’re ready to get in. In this case, make sure that recirculate is off. You’d only be recirculating crazy hot air. Roll down the windows and run the HVAC system for a few minutes until the AC starts blowing cold. Once all the hot air is released, roll the windows up and switch the system to recirculate. 

When you’re surrounded by pollutants

If you’re in a smoggy, smokey, or dusty environment, recirculate can help maintain a cleaner cabin. Air is filtered through the cabin air filter and kept at an even temp. If recirculate is turned off in dirty environments, the car will continuously inhale foul air, dirtying your cabin air filter faster. Moreover, these filters can’t block everything from entering the cabin.

Some people turn on recirculate if they’re stuck in traffic, regardless of the season. This stops the vehicle from ingesting as many exhaust fumes from other vehicles.

Make sure to switch it off after heavy use

Some say that relying heavily on recirculate can cause a stuffy cabin or even moldy HVAC components. If you’re concerned about this, you can simply execute what my family calls an “air change.” While you’re driving, roll down all the windows and let in fresh air. This is especially handy on long road trips. You can also turn off recirculate a minute or two before you’re done driving.

Generally, recirculate is most helpful in the warmer months. It can be kept off during colder times unless you’re actively defrosting your windows. In that case, recirculation is often used to ensure dry air defogs the glass.