A heater having a combustion chamber. The heater includes a hopper and a chute extending from an outlet of the hopper to the combustion chamber. The heater includes a chute extending from the hopper to the combustion chamber, a screw extending through the chute into the hopper, and a drive connected to the screw for turning the screw in a direction in which the flight would, but for downward forces, lift the fuel. The heater has a vane rotatably attached to the screw that rotates downward along the screw in absence of upward forces counteracting gravity. The vane is cambered to produce upward forces when turning with the screw beneath an upper surface of the fuel. The vane is biased toward the upper surface of the fuel to level the upper surface of the fuel and prevent the fuel from rat holing and arching.