Is there a rheem criterion 1 furnace? All I can find is info on a criterion II furnace and mine does not say criterion II. I want to change the filter, however, I don't know where the filter is. Can you tell me where the filter is located on a criterion furnace.

The name/brand has very little to do with where the filter is ,the installer had several options as to where the filter goes
For sure it most be in the air return part of the furnace/or ductwork.
In most systems where the returns are installed in the ceilings/with airhandler in the attic,they put the filter behind the return grill
If furnace is accessible in the basement,the filter is usually inside the furnace near the return duct,sometimes between the blower motor and connection of the return duct
Some are in a factory made filter holder that is between the return duct and the furnace/airhandler
Hope this helps