Iam redoing my stove pipe using Security Secure-Temp double wall pipe (matches the class A). From the ceiling box down I need a 45, 18" straight, 45, 30" straight and stove adapter. They don't make a 18" or 30" straight so I want to use a 12" straight and 3-9" adjustable for the 18" run and a 24" straight with another 3-9" adjustable straight then the stove adapter. This going into a nc13. Is it ok to use two adjustable pipes? Just want to make sure before I order.