Sheet metal question???

First time poster.Building my first RMH to heat my garage.I am using full size fire brick for my J tube and want to insulate the heat riser.My question is,with 1.5 inches of insulation around the riser,would sheet metal be sufficient as a wrap to contain the insulation.Do I need to worry about sheet metal melting or .I was thinking about using roofing metal that is 29 gauge or something similar.As a last resort a 16 x16 clay flue liner is an option but quite spendy.Any thoughts would be helpful.

Michael, sheet metal in that spot is perfect. Tho, i'd say get some galvanised, because of the rapid cooling of the gases, steam condensates a bit, and it might rust after a while. Tho everybody has used small barrels there, with no ill effect. So it takes time to rust.

Tho, 1.5 of insulation is a bit on the shy side. 2 would be better, assuming you're using perlite.