rigidly secured to the baffle 24 and extend upwardly therefrom outwardly of the intermediate coil 14 at their upper ends the straps 25 are formed to provide inwardly projecting hook portions 26 that have hooking engagement with the upper end of the intermediate coil 14 to support the baffle 24 in underlying engagement with the lower ends of the coils 14 and 15 in the embodiment illustrated the baffle 24 is in the nature of expanded metal such as stainless steel and is circular in outline so as to be only slightly less in diameter than the inner diameter of the outer coil 13 at one portion of its marginal edge the baffle is notched to receive the vertically extending portion 19 of the fluid conduit 12 the baffle 24 may if desired be made from mesh screen or of perforated metal sheet so as to permit flow of gases of combustion therethrough a second baffle 27 is disposed at the upper end of the outermost coil 13 and in axial alignment with the coils 13 15 and baffle 24 the second baffle 27 is imperforate and is preferably made from suitable material such as stainless steel as shown the baffle 27 is of smaller diameter than that of.