A combined device for heating domestic water and water for heating a room, said combined device comprising: - a storage tank for domestic water, - a domestic water circuit in fluid communication with the storage tank, - a heating water circuit, - a heat exchanger for a heat pump in which a heat transfer fluid is able to circulate, the heat exchanger being configured to perform a heat exchange: • between the heat transfer fluid and the domestic water present in the domestic water circuit, and • between the heat transfer fluid and the heating water present in the heating water circuit the heat exchanger including three pipes (64, 66, 68) interleaved with one another to define three fluid flow areas (70, 72, 74), said three pipes (64, 66, 68) comprising a first, a second and a third pipe forming: - a first flow area inside the first pipe, - a second flow area of annular section arranged between the first pipe and the second pipe, and - a third flow area of annular section arranged between the second pipe and the third pipe, in which the second flow area is configured to transport the heat transfer fluid and each of the first and third flow areas is configured to transport one among the domestic hot water and the heating water, characterized in that the wall of the pipe separating the domestic water from the heat transfer fluid is a double wall. - a storage tank for domestic water, - a domestic water circuit in fluid communication with the storage tank, - a heating water circuit, - a heat exchanger for a heat pump in which a heat transfer fluid is able to circulate, the heat exchanger being configured to perform a heat exchange: • between the heat transfer fluid and the domestic water present in the domestic water circuit, and • between the heat transfer fluid and the heating water present in the heating water circuit • between the heat transfer fluid and the domestic water present in the domestic water circuit, and • between the heat transfer fluid and the heating water present in the heating water circuit the heat exchanger including three pipes (64, 66, 68) interleaved with one another to define three fluid flow areas (70, 72, 74), said three pipes (64, 66, 68) comprising a first, a second and a third pipe forming: - a first flow area inside the first pipe, - a second flow area of annular section arranged between the first pipe and the second pipe, and - a third flow area of annular section arranged between the second pipe and the third pipe, in which the second flow area is configured to transport the heat transfer fluid and each of the first and third flow areas is configured to transport one among the domestic hot water and the heating water, - a first flow area inside the first pipe, - a second flow area of annular section arranged between the first pipe and the second pipe, and - a third flow area of annular section arranged between the second pipe and the third pipe, in which the second flow area is configured to transport the heat transfer fluid and each of the first and third flow areas is configured to transport one among the domestic hot water and the heating water, characterized in that the wall of the pipe separating the domestic water from the heat transfer fluid is a double wall.