A heat exchanger having a housing with a bottom, an upper wall and side walls. Additionally, onto two pairs of opposite side walls, a front wall and a back wall respectively, are connected a supply and a discharge for the gas to be cooled. A mechanism is provided in the housing for separating condensate from the cooled gas. The mechanism includes a series of corrugated vertical walls upon which are provided crosswise extending ribs forming vertical gutters extending only from the bottom up to the upper wall of the housing. Additionally, holes are provided in the bottom for the discharge of the separated condensate from the gutters via a collector. The collector extends from at least under the holes to under an opening which is provided in the bottom between the mechanism for separating condensate and the back wall.