In accordance with European Commission and Council Directive 2009/28/EC on renewable energy sources (RES) promotion, Latvia undertakes an obligation to reach 40 % of state energy consumption to be produced from the renewable energy sources by 2020. Despite the fact that Latvia is a rich in forests country, where wood is the most common renewable energy source, in year 2011 the amount of RES in total energy consumption was 33,1 %. In the transformation sector its use comprises 15 % only. Use of fossil fuel – natural gas remains a preference for both heat and electrical power producers, and it makes about 80% of total energy consumption. Nonetheless, an ongoing natural gas price growth stimulates its partial replacement with wood fuel, simultaneously ensuring conditions for effective wood fuel combustion. The goal of the research described in the dissertation is to make a research on co-firing of wood pellets and gaseous fossil fuel, evaluating influence of co-firing on emission production, efficiency, and produced energy volumes. In order to achieve the set aim and objectives a special pilot device for wood pellets and propane/butane co-firing was constructed at an accredited laboratory of Heat and Mass Transfer of the Institute of Physics. In addition an experimental research were held on the influence of permanent magnet on formation of swirling flow, formation of emissions, and efficiency, combusting wood pellets with and without propane/butane supply. Interaction processes of magnetic field and flame can be used to impact flow dynamics, flame temperature, and composition of combustion products. The results of the experimental research, as well as empirical data allow to run a complete analysis of co-firing and evaluating influence of magnetic field on emission production, efficiency, and produced heat energy volumes. The thesis has a high practical significance, aimed to increase the level of wood biomass use for energy production, as well as to assure its effective application. The research has multiple target groups, including heat energy producers, biomass combustion equipment manufacturers, governmental bodies and citizens.