This support provides proper clearance while supporting the weight of SuperVent Chimney. Use this piece in flat ceiling support installations. Install it between ceiling joists using headers to create a framework. Be sure the finishing plate is flush with the underside of the ceiling and the assembly is level and plumb. Nail or screw the Decorator Ceiling Support to your framing through the 12 predrilled holes in the Support. Use 6d or 2in nails or screws not included. When properly installed the Decorator Ceiling Support will hold up to 50ft of chimney. For SuperVent class-A chimney only. Inside diameter 8 inches.