Method of operating a laundry dryer, wherein the laundry dryer comprises: a laundry storing compartment for storing laundry to be treated, a rear channel (20b, 20c) for guiding process air at the backside of the laundry storing compartment, a back wall of the laundry storing compartment, wherein the compartment back wall comprises a plurality of back wall openings designed for passing process air from the rear channel (20b, 20c) into the laundry storing compartment, a rear wall forming at least a portion of a back cover of the dryer, a steam generation unit for generating steam to be supplied into the laundry storing compartment, and means for heating the process air for drying the laundry in the laundry storing compartment, wherein the means for heating the process air is a heat pump condenser or an electrical resistor heater, characterized by a nozzle unit (88, 300) comprising: one or a plurality of nozzle outlets for injecting steam generated in the steam generation unit into the laundry storing compartment, a steam conduit for providing steam from the steam generation unit to the nozzle unit (88, 300), and optionally a drain outlet for draining water from within the nozzle unit (88, 300) to the outside, wherein at least a portion of the steam conduit is guided within or in thermal contact with walls delimiting the rear channel (20b, 20c), so that there is a thermal connection between the rear channel (20a, 20b) and the steam conduit, and wherein the method for operating the laundry dryer comprises: activating the means for heating the process air before activating the steam generation unit, and activating a fan for guiding heated process air into said rear channel (20b, 20c) for warming-up the steam conduit and/or the nozzle unit due to the thermal connection before guiding steam through the steam conduit and/or the nozzle unit. a laundry storing compartment for storing laundry to be treated, a rear channel (20b, 20c) for guiding process air at the backside of the laundry storing compartment, a back wall of the laundry storing compartment, wherein the compartment back wall comprises a plurality of back wall openings designed for passing process air from the rear channel (20b, 20c) into the laundry storing compartment, a rear wall forming at least a portion of a back cover of the dryer, a steam generation unit for generating steam to be supplied into the laundry storing compartment, and means for heating the process air for drying the laundry in the laundry storing compartment, wherein the means for heating the process air is a heat pump condenser or an electrical resistor heater, characterized by a nozzle unit (88, 300) comprising: one or a plurality of nozzle outlets for injecting steam generated in the steam generation unit into the laundry storing compartment, a steam conduit for providing steam from the steam generation unit to the nozzle unit (88, 300), and optionally a drain outlet for draining water from within the nozzle unit (88, 300) to the outside, wherein at least a portion of the steam conduit is guided within or in thermal contact with walls delimiting the rear channel (20b, 20c), so that there is a thermal connection between the rear channel (20a, 20b) and the steam conduit, and wherein the method for operating the laundry dryer comprises: activating the means for heating the process air before activating the steam generation unit, and activating a fan for guiding heated process air into said rear channel (20b, 20c) for warming-up the steam conduit and/or the nozzle unit due to the thermal connection before guiding steam through the steam conduit and/or the nozzle unit. one or a plurality of nozzle outlets for injecting steam generated in the steam generation unit into the laundry storing compartment, a steam conduit for providing steam from the steam generation unit to the nozzle unit (88, 300), and optionally a drain outlet for draining water from within the nozzle unit (88, 300) to the outside, wherein at least a portion of the steam conduit is guided within or in thermal contact with walls delimiting the rear channel (20b, 20c), so that there is a thermal connection between the rear channel (20a, 20b) and the steam conduit, and wherein the method for operating the laundry dryer comprises: activating the means for heating the process air before activating the steam generation unit, and activating a fan for guiding heated process air into said rear channel (20b, 20c) for warming-up the steam conduit and/or the nozzle unit due to the thermal connection before guiding steam through the steam conduit and/or the nozzle unit.