42" Build Flue Question

[foxten]

I'm building a pizza oven in a covered porch and I'd like to vent the oven through my roof. What size insulated pipe should I use?

[JRPizza]

Foxten, are you following any plans or are you freestyling? The Forno Bravo Pompeii plans call for a 8" id pipe for ovens larger than 40". I used an 8" double wall pipe for my 39" oven that penetrated my shelter roof.

[foxten]

Just now seeing this. Thanks for the reply! I did see the section. I've actually made an adjustment and am making a 40" oven, so I'll be using the 6" double walled pipe. In the PDF, FB says to form a tapered flue to attach the Duratech Anchor Plate to, but I saw a video on youtube, where the guy just puts the anchor plate directly above the opening. He's putting a good 6" diameter anchor plate above a ~4" x 9" 6
rectangle. Is this OK?

[JRPizza]

You are better off providing a smooth(ish) transition for the chimney vs an abrupt change in cross section. The advice I give all new builders is to find a couple of builds here on the forum to emulate. I picked UtahBeehiver s and Gulf s builds to copy, and although my build looks nothing like theirs (mine is utilitarian vs theirs being works of art) I learned so much by trying to follow theirs. I don't think you will find any that do not strive for a smooth transition, being it built with bricks or a cast vent.