NOVELTY - A hydrogen generator comprises: a housing having a door; a cavity within the housing; a fuel unit removably disposed within the cavity and containing a hydrogen-containing material that can release hydrogen gas when heated; and a heater assembly comprising a heater disposed in the cavity for heating the fuel unit; where: the fuel unit is removable when the door is in an open position, and the housing is sealed when the door is in a closed position.    USE - The hydrogen generator and the method are useful for producing hydrogen gas (claimed).    ADVANTAGE - The hydrogen generator is cost-effective, and in which spent fuel units can be replaced with fresh ones without damaging either the hydrogen generator or the fuel unit. Also, the hydrogen generator is able to tolerate variability in fuel unit dimensions, particularly as a result of fuel unit shrinkage or swelling during use, while still maintaining good contact between the heater and the fuel unit.    DETAILED DESCRIPTION - A hydrogen generator comprises: a housing having a door; a cavity within the housing; a fuel unit removably disposed within the cavity and containing a hydrogen-containing material that can release hydrogen gas when heated; and a heater assembly comprising a heater disposed in the cavity for heating the fuel unit; where: the fuel unit is removable when the door is in an open position, and the housing is sealed when the door is in a closed position; the heater assembly is in a retracted position in which a gap is present between the heater assembly and the fuel unit when the door is in the open position; the heater assembly is in an extended position in which the heater assembly is disposed against the fuel unit when the door is in the closed position; and the hydrogen generator further includes a mechanism for moving the heater assembly between the retracted and extended positions, the motion of the heater assembly being actuated by a motion of the door between the open and closed positions. An INDEPENDENT CLAIM is included for a method of producing hydrogen gas with a hydrogen generator including a housing having a door, a cavity within the housing, a fuel unit removably disposed within the cavity and containing a hydrogen-containing material that can release hydrogen gas when heated, and a heater assembly including a heater disposed in the cavity for heating the fuel unit, which involves: (a) opening the door, thus causing a mechanism to retract the heater assembly toward the housing to increase a space within which the fuel unit can be disposed; (b) inserting a fuel unit in the cavity; (c) closing the door, thus causing the mechanism to extend the heater assembly toward the fuel unit and make contact therewith; (d) heating the fuel unit with the heater, thus releasing hydrogen gas from the hydrogen-containing material; (e) ceasing heating of the fuel unit; (f) opening the door, thus actuating the mechanism to retract the heater assembly toward the housing to create a gap between the heater assembly and the fuel unit; and (g) removing the fuel unit.