would result in extremely thin ends that are prone to easy breakage the invention allows the use of standard ferrules while reducing turbulence that occurs at the inner end of the ferrule when used in this disclosure the terms u201c upstream u201d and u201c downstream u201d shall relate to the flow of a heated fluid with u201c downstream u201d referring to the direction with or away from the flow and u201c upstream u201d referring to the direction against or towards the flow referring now to fig1 a typical fire tube boiler 100 is shown with a cooling tube 110 oriented longitudinally and parallel to a central axis 120 of the fire tube boiler 100 although the fire tube boiler 100 is shown in a horizontal orientation it may also be oriented vertically or at any angle therebetween without departing from the scope of the invention generally a fire tube boiler 100 will have multiple cooling tubes 110 of which only one is shown in the drawing for clarity each end of the fire tube boiler 100 may be covered with a tube sheet 130 131 having multiple holes 132 133 sized to snugly receive the ends of the cooling tubes 110 the pair of holes in the tube sheets 130 131 through which a cooling tube 110 is inserted may be coaxially aligned to maintain the cooling tube 110 in parallel relationship with the central axis 120 the cooling tubes 110 may be spaced apart to allow a cooling fluid such as water to circulate around and between the cooling tubes 110 to remove heat from the cooling tubes 110 by means of conduction the cooling fluid thus heated may.