A heating installation comprising: - a first circuit (C1) containing a medium; - a second circuit (C2) containing a medium; - a first heat pump arranged for heating the medium in the first circuit (C1); - a heat exchanger which is arranged in the second circuit (C2) and which is connected between a condenser and an expansion valve of the first heat pump in order to transfer heat from a working medium of the first heat pump to the medium in the second circuit (C2); and - a second heat pump arranged for heating a medium by absorbing heat energy from the medium in the second circuit (C2), wherein the second heat pump has its input side connected to the second circuit (C2) so that heat exchange between the medium in the second circuit (C2) and a working medium of the second heat pump is possible via an evaporator of the second heat pump , characterized in: - that the heating installation comprises a first accumulator tank (A1) and a second accumulator tank (A2) arranged in series with each other in the second circuit (C2) for accumulating the medium in the second circuit, wherein the second accumulator tank (A2) is arranged in the second circuit (C2) downstream of the first accumulator tank (A1) as seen in a flow direction from an outlet of said heat exchanger to an inlet thereof; and - that the first and second accumulator tanks (A1, A2) are alternately connectable to the second heat pump in order to allow medium in the second circuit (C2) to circulate between the first accumulator tank (A1) and the evaporator of the second heat pump in a first operating situation and allow medium in the second circuit (C2) to circulate between the second accumulator tank (A2) and the evaporator of the second heat pump in a second operating situation. - a first circuit (C1) containing a medium; - a second circuit (C2) containing a medium; - a first heat pump arranged for heating the medium in the first circuit (C1); - a heat exchanger which is arranged in the second circuit (C2) and which is connected between a condenser and an expansion valve of the first heat pump in order to transfer heat from a working medium of the first heat pump to the medium in the second circuit (C2); and - a second heat pump arranged for heating a medium by absorbing heat energy from the medium in the second circuit (C2), wherein the second heat pump has its input side connected to the second circuit (C2) so that heat exchange between the medium in the second circuit (C2) and a working medium of the second heat pump is possible via an evaporator of the second heat pump , - that the heating installation comprises a first accumulator tank (A1) and a second accumulator tank (A2) arranged in series with each other in the second circuit (C2) for accumulating the medium in the second circuit, wherein the second accumulator tank (A2) is arranged in the second circuit (C2) downstream of the first accumulator tank (A1) as seen in a flow direction from an outlet of said heat exchanger to an inlet thereof; and - that the first and second accumulator tanks (A1, A2) are alternately connectable to the second heat pump in order to allow medium in the second circuit (C2) to circulate between the first accumulator tank (A1) and the evaporator of the second heat pump in a first operating situation and allow medium in the second circuit (C2) to circulate between the second accumulator tank (A2) and the evaporator of the second heat pump in a second operating situation. <EOS>