A cartridge system is provided, including a liquid storage portion including a housing to hold a liquid aerosol-forming substrate; a mouthpiece having an outlet opening removably connected to a first end of the storage portion; and a heater assembly including an electrical heating element to heat the substrate to form an aerosol, and a porous capillary material having a first face contacting part of the heating element and to convey the substrate to the heating element by capillary action, the heating element disposed across the first face of the material, the liquid storage portion disposed at a first side of the heater assembly and a first airflow channel disposed at a second side of the assembly and defining an airflow path directed at a center of the heating element, and part of a second airflow channel extending to the outlet opening via a central channel of the housing.