Is it possible to purchase only the parts you need

Yes we make and offer the components individually. We can't say whether your local store offers them individually, however they can be ordered and purchased as single items. Remember, the parts all use the inside diameter of the chimney pipe to indicate their size. This is true even of the parts that attach on the outside of the pipe. For example, a 6" chimney pipe would use what is labeled as a 6" attic insulation shield, even though the attic shield goes around the 8" outside diameter of the pipe. If you have any questions, contact Selkirk's technical department at 800-748-0392 opt. 5.