Today: Tom and Ray explain the details of "Fresh" v. "Recirculate."

Dear Car Talk

Dear Car Talk | Apr 01, 2011

Dear Tom and Ray:

Can you please tell us which vehicles recirculate all of their inside air, rather than pulling in outside air? My wife is extremely allergic to smells, so pulling outside air into the car absolutely will not do. We were told that some Acura models recirculate the air continuously from the time the engine is started. Such recirculation would benefit us. On the other hand, we understand that the Lincoln MKZ has a switch that must be activated to recirculate the air; otherwise, it will pull in outside air. It is very important to us that no outside air get into the car's interior, due to my wife's sensitive condition. Can you please name any particular makes and models that might keep out truck exhaust, road tar, bus fumes, etc.? This presents a serious health issue for us, and we sincerely appreciate your advice. -- Roy


TOM: Gee, Roy, I'm not aware of any vehicles that completely shut out the outside air. Unless they're made by NASA.

RAY: Right. Without any outside air at all, you'd eventually suffocate in the car. And carmakers would never do that to their customers.

TOM: Heavens, no. Think of all the lost repair income!

RAY: Most cars have two settings for air that you can select from: Fresh (outside air) and Recirculate (inside air). Usually, there's a switch or button that allows you to choose one or the other.

TOM: But even the Recirculate setting allows some amount of outside air to come in (I would guess it's 10 percent), for the respiratory reasons stated above. So using the Recirculate setting certainly would cut down on the outside odors, but it wouldn't eliminate them completely.

RAY: Almost all cars also have cabin air filters that can stop certain allergens and dust particles. But the molecules that carry smells are too small to be stopped by such filters.

TOM: The only solution, if you really can't breathe ANY outside air, is to provide your own tanked air, like astronauts or scuba divers do.

RAY: But then you'd need a car with large front foot wells so that when your wife wears her scuba gear, she'll be able to sit comfortably in her fins.

TOM: Seriously, Roy, I don't know of any car that will completely block out all outside air. If your wife can handle some outside air, then any car with a Recirculate setting (and that's almost every car) should help. But if that's not good enough, then a doctor may be of more help than a couple of lousy mechanics. We wish you the best of luck!

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