How to insulate high temp ducting? 1

[rstevens]

I was wondering if someone could direct me to a standard or perhaps send some info my way on the following application:
Installation of a high temperature duct through an exterior wall made of sheet metal cladding.
The duct is 650mm in diameter (OD).
Estimated maximum temp is 400°C.
Sheet metal wall is single sided, has insulation layer w/ reflective surface on inside surface of panel.
The duct centreline is 7.8m above the floor level.

What I need to know is the convention for insulating the duct from the sheet metal such that it does not conduct heat to the wall.

Thanks!

 

[dicksewerrat]

Put a casing through the wall 4-6 inches larger than your duct. Use High temp insulation to seperate the two pipes. The actual size of the outer casing will depend on the R value of the insulation you choose. What is stopping the heat transfer to the air inside the building?