Firebox back wall removed

[MareOH]

I currently have insert in masonry fireplace. I was looking to upgrade it. After removing faceplate to get measurements I noticed back firebox wall had been removed. Is this safe on outside brick wall? Or should I have this rebuilt?

 

[begreen]

Can you post a picture or two showing what was removed?

 

[MareOH]

Yes. A little history the home had a chimney fire. Not exactly sure when but I do see a Crack in dry wall on second floor above where fireplace (and now insert is)

 

[begreen]

Looks ok to me, bholler can you verify? With the exposed brick being exterior, it should be 2 bricks thick. To reduce heat loss from the insert to the exterior, consider fabricating a blockoff plate and insulation between the back of the insert and the fireplace wall.