This unit is not meant to be used with B-vent pipe. Because it is a direct vent unit, it must pull its air from an outside source. The FMI direct vent piping is designed to perform that task. While B-vent pipe could theoretically be used to vent the exhaust from the unit, I am concerned about how the plumber would attach it to the unit properly and how the unit would breathe, as it would be pulling air from an enclosed wall cavity.
Also, the unit will not meet code if B-vent is used and could be considered a fire hazard.
Collin C. - NFI Master Hearth Professional
on December 18, 2012