Hello, Anyone know if his furnace has a filter and how to replace it? or the size for that matter? It has a compartment in the front and it isn't there. Model # is 117110ESUR. It's about 20-30 years old. Works great but want to maintenance filter. Can anyone help? Unit is screwed tight on four sides. SHould I get a screw driver and start dissasembling? Helllppp.....!!! Regards........Sara