Insulation for double wall vent pipe

[tikitime]

I have a boiler exhaust vent that I am trying to figure out the minimum required insulation thickness for. The vent is a stainless steel double wall pipe with a 1" air gap.

I am trying to select the fiberglass insulation thickness to keep the surface temperature below 130 degrees F for personnel safety. However, the air gap between the pipe is trowing me off. The 3E Plus program does not allow you to model a double wall pipe. Can anyone provide some insight?

Thanks!

 

[unclesyd]

We have a lot of double wall pipe vents that use 3" snap on insulation or 3" clam shell calcium silicate both with SS weather covering. These vents are steam heated with 25 lb steam and are considered man safe. I think we use 140F as the cutoff point.