I am currently affected by the US West smoke, so I bought some good filters for my furnace. I also bought extra filters and taped them in my ceilings where the air from the HVAC comes, for some extra filtering. I heard that I'm supposed to put my HVAC system to "fan on" (not heating nor cooling) so the air keeps passing through the filter and its quality improves. On the other hand, I also heard that if my system has "external air intake" I should turn it off completely.
The problem is that I don't know how to verify if I have external air intake. I watched some youtube videos and couldn't find anything similar to what I saw there. I looked for on/off switches everywhere and couldn't find any, except for one described below.
I took a picture of my furnace. I am not sure, but it seems to me the air flows in the direction of the arrow I painted in the picture, because the filters are right below the arrow and dust is on the up side. I also drew a black circle on the right side of the picture. There is a hole in the cover and it says "open" and "close", but given the size of that tube and where it is attached, I am not sure whether it is for external air intake or whether it is to fully close the heating system.
I should also note that all this is inside the garage, and the garage now has a much stronger smoke smell than the rest of my house, so I'm not sure if it my system is also taking air from my garage (instead of air from outside).
And a last detail, the filters don't really rightly fit my system, so air definitely goes through the side forming a path of least resistance. That is why I also taped some filters inside my house where the air comes.
What would be your guesses? Where should I be looking for things?
Thanks in advance.