An improved method and apparatus for supplying combustion air in a roof-fired furnace. Part of the combustion air, overfire air, enters through the roof of a roof-fired furnace at positions separate from the coal burners. The separated entry of overfire air ensures that the initial stages of combustion occur in a fuel-rich environment. A fuel-rich environment during the early stages of combustion favors the formation of molecular nitrogen and disfavors the formation of nitrogen oxides during combustion. The overfire air flows roughly parallel to the flow of combustion products emanating from the coal burners. The overfire air can be angled by vanes either slightly towards or slightly away from the combustion products, depending on how long combustion needs to be retarded in order to inhibit the formation of nitrogen oxides.