Heat pump apparatus for an air conditioning plant, such heat pump apparatus comprising: - an external unit which comprises: - a first containment body intended to be arranged in an external environment (E1, E2); - a first heat exchanger arranged in said first containment body and susceptible of operating as an evaporator for absorbing heat from an external air flow drawn from said external environment (E1, E2); - defrosting means operatively associated with said first heat exchanger and actuatable for heating the surface of said first heat exchanger; - an internal unit intended to be arranged in a channeling system of a climate-control plant adapted to introduce, into an environment, an ambient air flow coming from an ambient source; said internal unit comprising a second heat exchanger, thermally connected to said first heat exchanger, intended to be arranged in said channeling plant to intercept said ambient air flow, and susceptible of transferring heat to said ambient air flow; - a control unit operatively connected to said defrosting means in order to enable the operation of said defrosting means; said heat pump apparatus being characterized in that said defrosting means comprise an incandescent emitter configured for heating via irradiation said first heat exchanger, and such incandescent emitter comprises: - supply means intended to be connected to a first source of comburent air and to a second source of fuel gas; - a distribution chamber connected to said supply means in order to receive a fuel mixture of said comburent air and of said fuel gas; - trigger means actuatable for generating a combustion of said fuel mixture with consequent generation of heat and combustion products; - at least one emitting body, which is configured for receiving the heat generated by said combustion, and is provided with at least one radiant surface oriented towards said first heat exchanger in order to emit thermal radiations towards said first heat exchanger in a manner so as to heat, via direct irradiation, said first heat exchanger; wherein said control unit is operatively connected to said supply means in order to drive said supply means to supply said fuel mixture to said combustion chamber, and is operatively connected to said trigger means in order to drive said trigger means to trigger the combustion of said fuel mixture. - an external unit which comprises: - a first containment body intended to be arranged in an external environment (E1, E2); - a first heat exchanger arranged in said first containment body and susceptible of operating as an evaporator for absorbing heat from an external air flow drawn from said external environment (E1, E2); - defrosting means operatively associated with said first heat exchanger and actuatable for heating the surface of said first heat exchanger; - a first containment body intended to be arranged in an external environment (E1, E2); - a first heat exchanger arranged in said first containment body and susceptible of operating as an evaporator for absorbing heat from an external air flow drawn from said external environment (E1, E2); - defrosting means operatively associated with said first heat exchanger and actuatable for heating the surface of said first heat exchanger; - an internal unit intended to be arranged in a channeling system of a climate-control plant adapted to introduce, into an environment, an ambient air flow coming from an ambient source; said internal unit comprising a second heat exchanger, thermally connected to said first heat exchanger, intended to be arranged in said channeling plant to intercept said ambient air flow, and susceptible of transferring heat to said ambient air flow; - a control unit operatively connected to said defrosting means in order to enable the operation of said defrosting means; - supply means intended to be connected to a first source of comburent air and to a second source of fuel gas; - a distribution chamber connected to said supply means in order to receive a fuel mixture of said comburent air and of said fuel gas; - trigger means actuatable for generating a combustion of said fuel mixture with consequent generation of heat and combustion products; - at least one emitting body, which is configured for receiving the heat generated by said combustion, and is provided with at least one radiant surface oriented towards said first heat exchanger in order to emit thermal radiations towards said first heat exchanger in a manner so as to heat, via direct irradiation, said first heat exchanger;