As a builder who has built several homes with red iron frames I can tell you that I want my steel to be heated by the heat in the house, otherwise condensation can develop on the steel creating damage to the sheetrock/plaster. I had one inspector tell me that he had two homes in his jurisdiction that were "raining" inside from the condensation on the steel in the roof structure.Is there code language requiring placing insulation in a hollow steel structural tube in an exterior wall? (There will be no reduction in thermal transfer has the heat will flow around the metal shell.)
Not exactly sure if I understand your design but I would think that the steel tube would be cold in winter and hot in summer if not properly isolated. Vermiculite poured in the hollow steel tube comes to mine but it may have asbestos issues. Maybe another pour-able insulator could be used. I still believe your required to meet the building wall insulation requirement for your zone.
Can the the steel be wrapped with insulation or is that already being proposed? Spray foam?
As a practical matter I remove the insulation on the inside of steel columns after insulation inspection and before sheetrock, even with inspectors I know who allow me to leave it out the damn insulators insist on putting it in saying it violates Title 24 to leave it out.Hear the choir: http://www.eng-tips.com/viewthread.cfm?qid=403784