Gas and Oil Home Heating Furnaces - What do you mean no filters?

We recently discovered after buying our home that there were no filters on our furnace. The main intake we bought a new covering and had a filter installed in there. I just discovered under our hallway closet another small intake which is a small rectangle. Our house is only 1200 square feet and I am confused about this small intake. Do they make small filters for these? Will I be able to put a filter in this as well or will I have to do something else?

Did you pull the cover to the blower to see if the filter goes in there ??

Before you had the filter installed on the main intake we had someone come and look at our furnace. The guy said he has never seen a furnace with no filter on it, which is what we have. He is the one who suggested installing the filter on the main intake. I guess I am just confused as to why there was no filter in the first place and why there is a second small intake under the closet? My father-in-law said it might be part of an old heating system but I still feel air going in when my heater is on. Should I even worry about it?

You want to filter all air going back to the airhandler. It's easy enough for a tech or sheet metal guy to put in a filter rack right at the furnace or you can buy some filter media like what you use for window a/c's and put it behind the return grill.

I am not sure why on the smaller.. Did the guy put a filter in for you?

is it placed in the furnace, or right next to it in the ductwork?


as why not before, Who knows.. Maybe the last home owner was lazy to change them out or forget to put one in.

Do you have A/C? Did they check the coil to make sure it was clean?