The chimney in my 1941 Minnesota home runs through the middle of the home from the basement to the roof. As can be seen above, the chimney chase was never sealed. Every room it passes through above the basement is finished so the only access to sealing the chase is from the unfinished basement.
It's perfectly acceptable if the basement ceiling is the only location the chase is sealed from, isn't it?
I recently put in a high efficiency furnace that's vented through the rim joist so the chimney is currently unused. That being the case, is it ok to seal the chase with Great Stuff Fireblock spray foam ? If not, is there any sort of fireproof spray foam that's legal for this purpose? What's not shown in the picture above are the other three sides of the chimney that would be nearly impossible to seal with strips of aluminum but probably doable with spray foam.