Can not find where the filter for this furnace is. It is a gas Rheem Criterion II. Have watched YouTube videos but none look like mine. Thermostat keeps saying filter needs replacement.
Is it a down-flow or up-flow. Do you have vents/registers in each room on the floor or high on the wall/ceiling? If they are on the floor, you have a down-flow, and need to locate the intake side in your ceiling. In some homes, this is located near the thermostat. You will have a grate in the ceiling, behind that is most likely where the filter is/should be. If it is up-flow, you should have a filter in the lower part of the furnace itself. This looks like a down-flow, therefore you should have a grate or intake vent in the ceiling somewhere. It is possible that the previous owner took it out and never replaced it.