I am confused about my air filter size and placement.
The A/C unit is in the attic. The air inlet door/vent is downstairs near the thermostat. Behind the door/vent, is basically a cutout opening. It is about 20x40 in size, but looks like it was cutout with a blade. I can stick my head in there and look upward. It is basically a giant insulated chamber leading to a duct that goes into the inlet side of the A/C unit. The unit has a sticker that says the filters are located elsewhere ( or not in the unit itself) and that the correct size should be used. It doesn't say much else.
I am assuming the filters go behind the door/vent downstairs, over the 20x40 cutout. I have been putting two 20x20x1 filters, one stacked above the other, taped together.
What size filters should I be using, and is there possibly something missing that holds the filters?