A controlled mechanical ventilation installation of reversible dual flow thermodynamic type, including a primary circuit for the circulation of a first fluid having a first and a second loop connected to each other by a cycle-reversing four-way valve allowing to direct the first fluid in one direction or the other inside the first loop of the primary circuit, in which: - the first loop is equipped with a condenser/evaporator exchanging heat with an air blowing circuit, intended to blow air inside a building, of a first pressure reducer of the dual direction type arranged to let the first fluid pass in the two circulation directions of the first loop, of a first valve disposed between the four-way valve and the condenser/evaporator, and an evaporator/condenser exchanging heat with an air extraction circuit, intended for extracting air from the building towards the outside, disposed between the first pressure reducer and the four-way valve; - the second loop is equipped with a compressor and a heat exchanger disposed between the outlet of the compressor and the four-way valve, the heat exchanger being intended to be connected to means for heating a second fluid, in particular domestic hot water, said installation being characterized in that it further comprises: - a second valve disposed on the first loop of the primary circuit between the evaporator/condenser and the four-way valve; - a diverting branch including a first end joined to the second loop, between the exit of the heat exchanger and the four-way valve, and a second end joined to the first loop, between the first pressure reducer and the evaporator/condenser; and - a second pressure reducer disposed on the diverting branch, said second pressure reducer being arranged to let the first fluid pass only in the direction going from the first towards the second end of the diverting branch. - the first loop is equipped with a condenser/evaporator exchanging heat with an air blowing circuit, intended to blow air inside a building, of a first pressure reducer of the dual direction type arranged to let the first fluid pass in the two circulation directions of the first loop, of a first valve disposed between the four-way valve and the condenser/evaporator, and an evaporator/condenser exchanging heat with an air extraction circuit, intended for extracting air from the building towards the outside, disposed between the first pressure reducer and the four-way valve; - the second loop is equipped with a compressor and a heat exchanger disposed between the outlet of the compressor and the four-way valve, the heat exchanger being intended to be connected to means for heating a second fluid, in particular domestic hot water, - a second valve disposed on the first loop of the primary circuit between the evaporator/condenser and the four-way valve; - a diverting branch including a first end joined to the second loop, between the exit of the heat exchanger and the four-way valve, and a second end joined to the first loop, between the first pressure reducer and the evaporator/condenser; and - a second pressure reducer disposed on the diverting branch, said second pressure reducer being arranged to let the first fluid pass only in the direction going from the first towards the second end of the diverting branch.