NOVELTY - The fuel cell system comprises a fuel cell stack, and a reactant temperature conditioner that is coupled to a fuel source and an oxidant source, comprises a fuel inlet for receiving a fuel (40) from the fuel source, an oxidant inlet for receiving an oxidant (41) from the oxidant source, a fuel outlet coupled to the fuel cell stack to allow flow of a conditioned fuel (43) to the fuel cell stack and an oxidant outlet to allow flow of a conditioned oxidant (44) to the stack, and transfers heat energy from the oxidant to the fuel to arrive at the conditioned oxidant and the conditioned fuel.    USE - The fuel cell system is useful for providing an electrical energy to a load device such as industrial electric vehicle (all claimed) or forklift truck, and useful in automotive, aerospace and residential applications.    ADVANTAGE - The fuel cell system properly conditions the temperature of the reactants before the reactants are directed to the fuel cell or fuel cell stack in order to optimize the operation of the fuel cell system.    DETAILED DESCRIPTION - The fuel cell system comprises a fuel cell stack, and a reactant temperature conditioner that is coupled to a fuel source and an oxidant source, comprises a fuel inlet for receiving a fuel (40) from the fuel source, an oxidant inlet for receiving an oxidant (41) from the oxidant source, a fuel outlet coupled to the fuel cell stack to allow flow of a conditioned fuel (43) to the fuel cell stack and an oxidant outlet to allow flow of a conditioned oxidant (44) to the fuel cell stack, and transfers heat energy from the oxidant to the fuel to arrive at the conditioned oxidant and the conditioned fuel. The conditioner comprises a heat exchanger to transfer the heat energy from the oxidant to the fuel to arrive at the conditioned oxidant and the conditioned fuel. The system further comprises a coolant source coupled to the fuel cell stack, an oxidant humidifier (70) connected to the conditioner and the fuel cell stack to control a humidity of the conditioned oxidant prior to the conditioned oxidant flowing to the fuel cell stack, and a mixer coupled to the fuel outlet to allow a fuel exhaust of the stack to flow to the mixer. The fuel cell stack comprises a coolant outlet coupled to the conditioner to allow flow of exhaust coolant from the fuel cell stack to the conditioner to allow a transfer of heat energy to the fuel from the coolant, and an a coolant outlet coupled to the humidifier to allow flow of exhaust coolant from the fuel cell stack to the humidifier. The conditioner is coupled to the humidifier to allow flow of the exhaust coolant to the conditioner. The fuel cell stack is electrically coupled to a load device to provide electrical energy to the load device. The mixer is configured to mix the fuel exhaust with the fuel to result in a mixed fuel provided to the conditioner. The conditioner is coupled to the fuel outlet to allow the fuel exhaust of the stack to flow to the conditioner. The conditioner comprises a mixing portion to mix the fuel exhaust with the fuel prior to the conditioner transferring heat energy from the oxidant to the fuel to arrive at the conditioned oxidant and the conditioned fuel. An INDEPENDENT CLAIM is included for a method for operating a fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of a fuel cell system.    Fuel (40)    Oxidant (41)    Conditioned fuel (43)    Conditioned oxidant (44)    Oxidant humidifier. (70)