While replacing the filter on my Rheem 90 plus upflow furnace, a piece of what appears to be insulation (aprox. 18in by 12in) fell off of the right inside housing of the furnace. A picture of it can be seen on page two (bottom right below the line to the Draft Inducer) here:
Does anyone know what the purpose of this piece is and if it is necessary? The piece that unglued is really dirty so I would probably have to find a new one.