I am having a mason re-stone fireplace but there is an issue with the old steel heatilator.
Old steel heatilator has 2 vents on each side of chamber, one low, one high. Brick is in the middle of these 2 voids that are right on the outer wall of the fire box. I am assuming the vents are lower 'in', upper 'out' for convection of heated air that flowed next to firebox.

There never was a noticable heat "outflow" from the vents. Can I have a mason 'brick' along the outside of the firebox and eliminate the voids (filling them in) . . the voids that had the intention to flow radiated/convected heat?

The previous stonework was built "away" from the wall(vents). the vents were hidden - but were not covered - by a partially free-standing stone work.

I want to restone the exterior, did not want the job of removing the firebox, but am uncertain if I can have the mason just stone-over these vent openings without creating a firestop from the outer shell. (hopefully picture attached helps). Thanks, Jim