Getting ready to put in my VC 1990 and have questions about the support box. I have the Duravent 6DP-CS11 box not installed yet and the Duravent triple wall that goes above that out the roof (pictures below). I would like to use 6" double wall pipe from the VC stove to the ceiling then the box accepts the triple wall already on the other side. It seems like the box will only accept single wall on the inside ceiling side. What am I missing here? Is there an adapter that I need? I do not have the double wall pipe ( only have a few pieces of Ameri-tech DCC and can't find anymore). I will probably go with double wall duravent. I am mainly using double wall for clearance purposes