The experimental study and analysis of the effects of wheat straw pellets co-firing with propane flame flow and co-combustion with wood pellets on the processes of thermo-chemical conversion and heat energy production are carried out with the aim to improve the combustion conditions and applicability of wheat straw as an alternative heat energy source. The processes of wheat straw thermal decomposition and combustion of volatiles were studied experimentally using a small-scale pilot device with a heat output up to 2 kW and a test device with a heat output up to 20 kW. To improve combustion conditions, the swirl enhanced mixing of the flame components is used. The analysis of the effect of wheat straw co-firing has shown that additional heat energy supply into the biomass layer provides enhanced biomass thermal decomposition completing the combustion of volatiles and increasing thus the produced heat energy at thermo-chemical conversion of wheat straw pellets. The combustion characteristics for wheat straw pellets can be also improved by providing co- combustion of wheat straw with wood pellets. A very important result is that combustion efficiency, composition of emissions and heat output at wheat straw thermo-chemical conversion can be improved by providing co-firing and co-combustion of wheat straw with wood.