As my two other threads indicate I am looking to replace my old insert. Today I pulled off the surround and found something surprising almost shocking. When whoever installed it they removed the back of the firebox and the smoke shelf to make it fit. The manuals for both the Napoleon and the Osburn state that they are to be installed into a code compliant masonry fireplace. I would say that this is not a code complaint fireplace anymore. I decided to call a local mason to see if he would look at it and he told me that it should be fine since the fireplace is on the exterior. From what I can see what is behind the insert is cinder block and beyond that would be the brick that covers the outside of the fireplace. He did not think an insert would get hot enough to crack the cinder block. Feeling around the lintel it is steel going up 8-10 inches and on the sides around the lintel are stuffed with some sort of dense white insulation (hopefully not asbestos) This fireplace was added to the house in the late 1960's or early 1970's. Any advice? I sent an email to Osburn to see if they have any advice on this. The only thing I can think of is they are worried about interior fireplaces heating up wood framing on the other side of the firebox. ***Update*** I got a reply back from Osburn, they said that the rear of the insert will not get super hot just as the mason said and being an exterior wall it would probably be ok however he said for insurance and liability purposes I would have to have a certified dealer look at it, fair enough. The other mason I called told me to call back tonight. If he says the same thing I will not worry about it. I am thinking of installing a block off plate and leaving the surround off to get more heat out into the house. I would tile the entire old firebox before doing this though so it would look nice as well as be functional. Does that sound like a bad idea?