the 3 side pipes protrude into the 3 upright sections ,not quite halfway into them , my rough calculations of flow using the 5 inch stainless flue sections ,meant 2 of them would not be enough , 3 of them would be more than the 6.25 pipe , but with the bends and turns plus protruding sections would cut back on the extra CSA . I now have all the sections up and the cowl , just to wrap it in rockwool and sheet around the pipe work , closed the stove top surface up and closed the stove door , opened the primary air and there is a slight draw already , going to try a smoke test ,or if i can get the top glass in and seal off the whole top assembly for a test fire .