An aerosol generating system comprising: • an aerosol-forming article (102) comprising an aerosol-forming substrate (12) and a mouthpiece portion (24) for allowing a user to draw air through the substrate; and • an aerosol generating device (100), the device comprising a housing (10) having proximal and distal ends and comprising at least one external surface and one internal surface, the internal surface defining an open ended cavity (22) at the proximal end of the housing in which the aerosol-forming substrate is received, the cavity having a longitudinal extent between its proximal and distal ends, a heater element (14) within the cavity configured to heat an aerosol-forming substrate received in the cavity, and an air inlet (26); • wherein the system comprises a first air flow channel (28) extending from the air inlet to a distal end of the cavity, wherein the first air flow channel extends between the heater and the external surface of the housing along at least a portion of the longitudinal extent of the cavity, and a second air flow channel extending from the distal end of the cavity to the mouthpiece portion.