In general, does air recirculated in the cabin (i.e. when the re-circulate button is engaged on the dash) pass again through the cabin air filter?

I know that the cabin air filter filters outside air before it enters the passenger space, but is it also used in closed re-circulation?

Specifically: I have a 2006 Honda Civic which only has 1 filter. Am I re-filtering the air as I'm running it on re-circulate mode?

While I'd like to think the air is getting continually filtered, I also don't think it's a good idea to pass cabin air back over all the leaves and pollen and crap the filter took out in the first place, probably makes things worse.

The filter I changed was in the glove box and it had leaves and twigs and all kinds of stuff in it, so I know it is filtering outside air. It seems counter-intuitive to send inside air back over all the garbage in the filter.

  • 3
    Great question! Something I hadn't even considered :o) Commented Mar 1, 2016 at 20:03

1 Answer 1


Cabin air filters will usually filter the air on either setting if located on the cabin side of the firewall. But even in recirculation mode, outside air will make its way in. Just be sure to replace it as frequently as your manual suggests. However, filters located under the hood at the air intake will not filter recirculated air.

Edit: I decided to look for confirmation and found this:


I can also add links to confirm that a little bit of outside air will still make its way in on recirculation mode if it's necessary.

  • Do you have any diagrams showing this? Commented Mar 1, 2016 at 21:43
  • It makes sense that even when re-circulating the system would have some fresh air intake, which would obviously go through the filter. Commented Mar 1, 2016 at 22:31
  • So, would terminology, i.e. in the service manual, suggest more precisely what's going on? For the record, I just used the term "cabin air filter" off the top of my head so you knew which I was talking about, not really sure if that's the technical term for how it is used in the Civic. Commented Mar 1, 2016 at 22:33
  • Some cars have varying or adjustable levels of outside/inside intake air, but to blanketly state that 'the recirculation setting will still allow some outside air in anyway so you don't suffocate' is wrong. My dodge ram completely closes off the outside air vent, and I'm sure most other cars do the same. It would take many hours if not days to suffocate inside a car, even if it were completely air tight (which...they aren't).
    – Nick G
    Commented Mar 2, 2016 at 18:35
  • @Paulster2- Can't seem to locate a diagram of the ventilation system with a filter included unless it's one under the hood, which will only filter outside air. But filters located in the cabin, either behind or under the glove compartment, will filter both because it's located inside the firewall. Commented Mar 2, 2016 at 20:01

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