I am getting ready to order all my chimney materials and a few questions. First I am installing an econoburn and am installing a barometric damper. My install is simply out the back of the boiler then a tee or 90 then the barometric damper then straight up through the roof then continue straight up out side the building up another 20 feet or so. So it's just out the boiler then 90 then straight up. Since a good portion of the venting will be outside I will be using the double wall SS UL103 piping( the expensive stuff) My question is this, all the barometric dampers I have seen are just single wall black pipe. So is single wall BD ok? If so then my plan is to come off the back of the boiler with plan black stove pipe with a black stove pipe tee then the BD then transition to the double wall SS. This will leave me with no more than about 3 feet of plain black stove pipe. I am trying to keep the flue temps up, and don't know if this is an issue or not.