Typically, a ceiling support box or round ceiling support is used to make this sort of transition. The support serves a dual purpose in the fact that it supports the chimney above the ceiling and allows a safe transition point. An item such as the DuraPlus All-Fuel Chimney Round Ceiling Support
is a good example of a support for a flat ceiling, while a pitched ceiling is better served by an item such as the DuraPlus All-Fuel Square Cathedral Ceiling Support Box
. If you have already selected the brand of chimney pipe you wish to use, please advise and I will assist you in selecting the proper components. Each pipe brand has different attachment methods and components, so it is important to use the same brand of parts.