A cartridge for an aerosol-generating system is provided, the cartridge including: a liquid storage portion configured to hold a liquid aerosol-forming substrate; and a heater assembly including: an electrical heating element configured to heat the liquid aerosol-forming substrate to form an aerosol, and a capillary body having a porous outer surface and being configured to convey the liquid aerosol-forming substrate to the electrical heating element, the electrical heating element being disposed along the porous outer surface, the liquid storage portion being disposed at a first side of the heater assembly and an airflow channel is disposed at an opposite side of the heater assembly to the first side and adjacent to the electrical heating element, defining an airflow path that extends past the electrical heating element and is configured to convey the aerosol. A heater assembly and an aerosol-generating system are also provided.