Abstract: A turbulator comprising a strip of metal formed into a generally zig-zag longitudinal extending element for insertion into a fire tube of a furnace which so deflects gases passing through the tube as to break up laminar flow and thus improve heat transfer. The apices at the junctures of the legs of the element, which contact the interior wall of the fire tube, are rounded both longitudinally and laterally of the length of the strip to insure non-scratch contact with the interior wall during insertion and retraction whereby to prolong the life of the tube by eliminating zones sensitive to corrosion.