Abstract: A furnace system suitable for independent use and for retrofitting conventional central heating oil furnaces to permit controlled continuous and efficient combustion of fragmented wood type fuels. Wood chips or other fuel fragments are trickle fed into a refractory wood type combustion chamber. For retrofitting an oil furnace the oil burner gun is removed. A flame tube adapter couples the wood type fuel combustion chamber into the oil combustion chamber and heat exchanger plenum of the conventional furnace. The oil burner gun of the retrofitted furnace is used to ignite the wood chips or other fuel fragments during start up. A blower establishes forced draft. The furnace system includes automatic controls for sequencing operation of the elements of the retrofitting furnace system. An independent wood chip furnace system is also described.