Each of the twenty-foot lengths of carbon steel tubing was cut into fourteen flues, each flue 16-3/8" long, using a power band saw.  Two lengths of tubing were cut at a time and allowed to drain of cutting fluid.  Flues then had their ends sanded perpendicular using a belt sander to remove cutting burrs and to insure ends are flat.  Flues were then rotated at a slight angle to the belt to apply a slight bevel to the outside edge of the flue so that there were no burrs to catch as they were pushed into the flue sheets.