A heat exchanger for a solid-oxide fuel cell assembly. A plurality of parallel tubes conveys fuel cell stack exhaust gas from a first manifold means to a second manifold means. The tubes are highly corrugated to increase the wall area and decrease the wall thickness. The tubes are disposed in a jacket through which is passed incoming air to be heated. The tubes may be linear between two manifolds, or they may be curved such that the first and second manifold functions are accommodated within a single component.