An aerosol-generating device includes a heating chamber structure, a heater coupled to the heating chamber structure, and a compression assembly. The heating chamber structure defines a fixed-volume enclosure and is configured to hold an aerosol-forming substrate within a first region of the enclosure. The heater is proximate to a first surface that at least partly defines the first region and is configured to generate heat that is transmitted into the first region to cause the aerosol-forming substrate to form an aerosol without any combustion. The compression assembly includes a compression plate and a compression actuator. The compression plate and the first surface define opposing boundaries of the first region. The compression actuator moves the compression plate through the enclosure to adjustably compress the aerosol-forming substrate in the first region against the first surface.