In this current project, I've built three separate arches. This will enable the owners to both close the mouth (which isolates the dome) as well as the face arch (which is in front of the flue). This does not replace the damper in the insulated metal chimney which will still function to close the chimney when the fire is out.
As will all current ovens there are two air channels on either side of the mouth. These will be closed by specially cut bricks and the second door as well.