A housing for a heat exchange apparatus including a fluid passageway partially defined by a baffle plate having an extended portion. The heat exchange apparatus further includes an array of fluid conduits extending through the fluid passageway. The housing includes a plurality of housing members each having a wall and at least one flange extending from the wall. The flanges of adjacent housing members are joined at a flange joint, and the flange joint is configured to fixedly receive the extended portion of the baffle plate. The apparatus also includes a plate member is provided within the fluid passageway and intumescent material fills a gap between the baffle plate and the plate member. Additionally, a second baffle plate is provided that defines a portion of a second fluid passageway, where a refractory gasket and a layer of intumescent material are provided between the first and second baffle plates.