Method of extracting syngas between the zone in a furnace where oxygen-starved combustion of biomass occurs and the zone in the furnace where secondary air is added to complete combustion, conditioning and cleaning the extracted syngas, and delivering it in a metered amount to the oxidizer or upstream of the oxidizer to reduce or eliminate the need for additional fossil fuels once the oxidizer has achieved its operating temperature. The gasifier or furnace burns solid waste and produces a syngas containing relatively high levels of CO, which is extracted from the furnace, conditioned, and introduced into an RTO as a fuel source. In certain embodiments, no extraction of syngas from the furnace takes place; the furnace conditions are manipulated so that normally undesirable levels of CO and other VOC's remain in the process stream. The heat from the furnace is used as intended (e.g., to heat a dryer), the stream is conditioned, and ultimately proceeds to a downstream RTO. Since the gas stream remains rich in CO and VOC's, its fuel value in the RTO is substantially higher than otherwise would be the case.