A fuel cell system includes a fuel cell stack and a reactant temperature conditioner. The conditioner includes a fuel inlet for receiving fuel from a fuel source and an oxidant inlet for receiving oxidant from an oxidant source. The conditioner is configured to transfer heat energy from the oxidant to the fuel to arrive at a conditioned oxidant and a conditioned fuel. The conditioner has a fuel outlet coupled to the fuel cell stack to allow flow of the conditioned fuel to the fuel cell stack and an oxidant outlet to allow flow of the conditioned oxidant to the fuel cell stack.