B vent insulation and firestop woes

I have a recently installed B vent that runs through a vertical space inside of our house that used to be a brick chimney that vents our furnace and HWH from the basement to the roof(we took down the original crumbling chimney). The B vent runs up along an exterior stud wall which was not insulated. There were no firestops installed around the B vent at each floor level. We didn't cut through any floors since it was kind of a vertical shaft space. There are spaces above the ceilings of adjacent rooms that open into the"shaft" area. I am worried about these holes. I need to close these up, don't I? Since openings (I think there are 2 or 3 about 24" x 24") are not accessible (I can just see them) any thoughts on how to close them? Can I use that Great Stuff foam insulation? Does the wall around a B vent need to be a fire rated wall in a house? What is the purpose of the firestop? If I have a direct shaft up, is this legal or do I need to install fire stop at each floor of the shaft? Needless to say, the contractor didn't know what he was doing and the work was not inspected. We may open the wall this summer to correct these issues. I just read on here about insulation to use around a B vent. Sounds like rock wool. Our house is cold and I am worried about condensation forming on the uninsulated exterior wall with warm B vent just inside. Any thoughts on this would be apprciated. Robin
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Yes.

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too wordy of a question ha?
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