In a house now for 6 months, just learned today I should have changed my filter twice already, whoops.
I have a zoned system - two furnaces, one in the finished attic on its side, one in the basement. As far as I can tell, there is only one filter - in the attic stairway, there's a big grille on the wall, and behind that is a filter which is connected to a duct leading to the furnace. Easy. There is nothing like this at all in the basement - the ducts don't lead to any sort of grille. Is this normal?
Including a couple of photos of the furnace in the basement, from the two sides I can access. The ducts are covered in some kind of insulation, then lead out into the home.