In your last picture is their a "door" that opens by the orange dot? This where a filter goes on some units.
If there is no filter in your heater then you need the one in the vent. Size sounds correct for a filter. Probably easer to replace.
I had a heater that had the filter outside of the heater but where the return duck work entered the heater. The heater had no place for a filter.
I would say one filter for return air and one filter for outside air coming into the house.
|