Chimney liner insulation and efficiency

steve_173

I’m going to have my clay lined chimney lined with a 316L stainless liner (~30’, 8” ovalized). This is part of a gas conversion. The liner will take a hot water tank and two boilers, all natural gas.

I can’t get a straight story on whether insulation is needed or even desirable for better efficiency. If it is more efficient, by about how much?

Vermiculite is cheaper than a blanket wrap but I don’t like the idea of the stuff unintentionally coming out or being impossible to get out in the future. The wrap seems like a better long term option. Any thoughts one way or the other?