The Only Non-Vented Thimble!
All other UL-103 Pressure Stacks require ventilation in their roof thimble assemblies.
As DWKL is the first ONLY fiber insulated pipe produced in North America, we decided to also fiber insulate our thimbles. This means the assembly does not require air ventilation for zero clearance to combustibles at the roof.
Jeremias sees this has an added safety feature as we know owners do not want this continuous air ventilation losses (and how they address that after installation).