Vent Opening / Height Question

[McGooster]

Hey everyone, I am almost finished with mortaring dome and have started thinking about my chimney design but want to make sure I have this right before I start. Right now I am building a 36" ID Oven and I have the vent transitioning from the outer arch to a 10x10" area where I will mount a Durvavent 6" Anchor Plate for a SS 6" opening Chimney Pipe. My question is: Is there a specific height that the brick vent area needs to be, before the pipe? Right now from bottom of where arch starts transitioning to vent -- to where the mounting plate would be is 7.5". Is that ok? Or do I need to add a few layers of brick to increase this?

Also random question. I have been using HeatStop50 mortar for my oven. On the outer Arch + Vent transition, should I use the same mortar or standard "S" type structural mortar?

Thanks again for any insight here.

[mongota]

I don't think you need to add more courses of brick to raise the chimney anchor plate. I think your drawing looks fine as is. I added a single course of brick (on edge) to transition from the curved top of the arch to a flat surface on which to mount the anchor plate.

I'd continue using HeatStop on your arch. If it's firebrick that will see flames or high-temps, use HeatStop or equivalent.

[david s]

Just as a fireplace requires a decent hood for the smoke to collect before exiting into the flue pipe or chimney, so does an oven. Until the oven and pipe have heated up somewhat the draw is quite poor and some smoke is likely to escape out the front. Because the system is a cross draft one, rather than an updraft, the draw needs to be sufficient to draw the flame and smoke sideways before exiting. This makes all the more reason to have a generous collection area above the oven mouth. Additionally a smooth rather than a stepped form is more efficient to provide a smooth flow.

Regarding the Heatstop, use whatever you have, but as most builders have found homebrew adequate for their domes and the fact that the gallery sees much lower temperatures, in normal operation it won’t even see any flame impingement, the homebrew is a suitable solution.

[McGooster]

Thank you mongota and David for your input. Super helpful. I'm going to add a layer or two, to the hood just to ensure it has a decent space to collect the smoke.