The present invention relates to a ventilation duct (200) intended to the air conditioning air from a rearing building, defined by at least one wall (p1, p2) isolated from a thermal point of view, and designed to be adjacent to said vessel, so that said sheath can be placed around at least one outlet orifice (bs) of hot air coming from said building, produced by the presence of animals to the inside of the - latter and around an input (ad) of the admission of fresh air in the building, the air flow duct (200) including a heat exchanger (210) intended to be transferred to the incoming air flow, a portion of the calories contained in the flow of air leaving. According to the invention, the heat exchanger (210) is formed of a metal wall (pm) disposed inside said casing and at a short distance from said wall insulated (p1, p2) so as to delimit a passage (ps), between an input (and) carried out through said wall insulated and an air outlet (st) arranged to be positioned in the screw - to - respect to the input (ad) for admitting air into the building, an outlet conduit (cs) passing through an end wall (px) of the air flow duct (200) for the passage of the flow of outgoing air having yielded of the calories to the metal wall (pm)). The incoming air flow is preheated by the heat taken from the flow of air leaving. The consumption of energy for heating the building in the winter period is markedly reduced. The simple structure of this sheath is economical to manufacture ventilation. It can easily be adapted on an existing building.
