You say you have the triple wall pipe for your stove, so I'm guessing it's used. A reputable dealer would have alerted you to the need for the appropriate pass-throughs to complete your
project. If your pipe is in fact used, inspect each section for any damage...any damage whatsoever. Even the smallest dents deform and reduce the interior clearances inside the pipe, which can affect the heat transfer to surrounding combustible materials. Inspect the innermost liner of the pipe, looking for ripples, dents or perforation of any kind...especially separated joints. Use appropriate connectors and terminators and NEVER mix brands or make-shift parts in one chimney system. Proper installation with appropriate parts are the only thing between your solid-fuel heating system and healthy living. Don't scrimp.