To prevent a heat exchanging efficiency from being deteriorated by preventing the increase of the thickness of a condensate sticking to a fin.
The offset type fin is used as an outer fin 132 in which many segments 132a are discretely arranged with prescribed spaces δ in the flowing direction of combustion gas. Thus, since the film of the condensate can be finely parted by the spaces δ, the condensate sticking to the fin 132 does not entirely spread in the outer fin 132 and falls (separates) from the outer fin 132 at the parted parts (spaces δ). Accordingly, when the increase of the thickness of the film of the condensate can be prevented, the increase of thermal resistance by the condensate can be suppressed. The deterioration of the heat exchanging efficiency and the early corrosion of the outer fin 132 can be prevented.
OKOCHI SHIGEKI
MAEDA AKIHIRO
