Single Wall Boiler Vent - Combustibles Clearance

[molo]

I am building a basement window cover. There is a boiler vented with 3" Stainless Steel vent pipe through the basement window opening. I would like to incorporate a 2" rigid foam Dow board into the new cover.

Does anyone know the required clearance between the vent pipe and the foam board?

Thank You,
Bill

[hj]

6" is the standard for single wall vent pipe.