A heating installation comprising: - a first circuit containing a medium; - a second circuit containing a medium; - a first heat pump arranged for heating the medium in the first circuit; - a first heat exchanger which is arranged in the second circuit 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; - a second heat pump arranged for heating a medium by absorbing heat energy from the medium in the second circuit; and - a second heat exchanger which is arranged in the second circuit in order to transfer heat from the medium in the second circuit to water in a water supply line that is intended to be heated in order to provide tap hot-water, this second heat exchanger being connected to the second circuit downstream of the second heat pump as seen in a flow direction from an outlet of the first heat exchanger to an inlet of the first heat exchanger, characterized in: - that the heating installation further comprises a third heat exchanger which is arranged in the second circuit in order to transfer heat from the medium in the second circuit to the water in said water supply line, this third heat exchanger being connected to the second circuit upstream of the second heat pump as seen in said flow direction; and - that said second and third heat exchangers (12, 14) are arranged in series with each other in said water supply line, the second heat exchanger being connected to the water supply line upstream of the third heat exchanger to thereby allow the second heat exchanger to preheat the tap hot-water in a first step and the third heat exchanger to preheat the tap hot-water in a subsequent second step. - a first circuit containing a medium; - a second circuit containing a medium; - a first heat pump arranged for heating the medium in the first circuit; - a first heat exchanger which is arranged in the second circuit 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; - a second heat pump arranged for heating a medium by absorbing heat energy from the medium in the second circuit; and - a second heat exchanger which is arranged in the second circuit in order to transfer heat from the medium in the second circuit to water in a water supply line that is intended to be heated in order to provide tap hot-water, this second heat exchanger being connected to the second circuit downstream of the second heat pump as seen in a flow direction from an outlet of the first heat exchanger to an inlet of the first heat exchanger, - that the heating installation further comprises a third heat exchanger which is arranged in the second circuit in order to transfer heat from the medium in the second circuit to the water in said water supply line, this third heat exchanger being connected to the second circuit upstream of the second heat pump as seen in said flow direction; and - that said second and third heat exchangers (12, 14) are arranged in series with each other in said water supply line, the second heat exchanger being connected to the water supply line upstream of the third heat exchanger to thereby allow the second heat exchanger to preheat the tap hot-water in a first step and the third heat exchanger to preheat the tap hot-water in a subsequent second step.