The invention relates to a method for operating a fuel cell device (23) in a low-pressure chamber (7) comprising a reformer (2) for producing a hydrogenous gas. According to the invention, air for operating the fuel cell stack (1) and the reformer (2) is introduced into the low-pressure chamber (7), which flows around components of the fuel cell device (23) that are located inside the low-pressure chamber (7), and which is supplied to the fuel cell stack (1) and to the reformer (2). The air for operating the fuel cell stack (1) and the reformer (2) absorbs convective heat from the components of the fuel cell device (23) that are located inside the low-pressure chamber (7) and absorbs gases from possibly occurring leaks of the components of the fuel cell device (23) that are located inside the low-pressure chamber (7). In addition, the air transfers heat to a cooling circuit (8), and this cooling circuit (8), in turn, transfers heat to a heating circuit (10, 11).