The fuel gas system (100) for a vehicle (1) comprises: —a filling device (50) having an outlet pipe (56); —a first circuit (11) for providing fuel gas to an engine (8) of the vehicle, and including: —a first tank (12); —a first supply line (13) connecting the first tank (12) and the engine (8); —a first filling pipe (14) connecting the filling device outlet pipe to the first tank (12); —a second circuit (21) for providing fuel gas to a thermic device (9) capable of heating, cooling or refrigerating, the second circuit (21) including: —a second tank (22); —a second supply line (23) connecting the second tank (22) to the thermic device (9); —a second filling pipe (24) connecting the filling device outlet pipe (56) to the second tank (22). The first circuit (11) and the second circuit (21) are configured to be in fluid communication: —in a filling phase, when fuel gas flows in the first and second filling pipes (14, 24) from the filling device (50) towards the first and second tanks (12, 22); —and in a working phase, when fuel gas flows in the first and second supply lines (13, 23) from the first and second tanks (12, 22).