Described herein are portable fuel cell systems for producing electrical energy. The portable fuel cell systems include a fuel processor including a reformer and a burner. The reformer receives fuel and outputs hydrogen using the fuel. The burner processes fuel to generate heat. The system also includes a fuel cell configured to produce electrical energy using hydrogen output by the reformer. The system also includes a heat exchanger configured to transfer heat generated in the fuel cell or generated in the fuel processor to a reactant fluid.