8'' DuraPlus 36'' Square Ceiling Support Box - 8DP-CS36 This DuraPlus component supports up to 40' of chimney pipe with a built-in starter section. DuraPlus is a triple-wall, all-fuel chimney, used with flat, vaulted, or cathedral ceilings. Square Ceiling Support box features a sleek black finish to add pleasing aesthetics to the fully functional build. Diameter: 8"