The present invention relates generally to furnace systems and more particularly, but not by way of limitation, to a split-ring assembly for sealing a junction between a catalyst tube and a furnace. In one aspect, the present invention relates to a ring-seal assembly. The ring-seal assembly includes a housing ring coupled to an outer surface of a furnace. The housing ring is disposed around a circumference of a tube proximate a junction with the furnace. The ring seal assembly further includes a brush seal that is at least partially disposed within the housing ring. The brush seal is disposed around the circumference of the tube. A plurality of brushes extend radially inwardly from the brush seal towards the tube.