A method of producing a fuel substance by separating materials in a recycling operation based on BTU component content is provided. A stream of materials including non-sorted, heterogeneous, recycled materials is shredded. The stream of materials is separated into heavy and light materials with a separator that discharges the light and heavy materials in respective light and heavy material streams. Ferrous and non-ferrous materials are magnetically separated from the heavy material stream. The non-ferrous materials are discharged to a screen for further separation. The light materials are processed through a rotary trommel and a non-ferrous metal separator to separate the light materials into fine, coarse, and non-ferrous metal materials, the coarse materials having a BTU component content of at least four thousand BTU's per ton. Low density materials are separated from the coarse materials with a low density separator, thereby increasing the BTU component content of the coarse materials.