The present study focuses on the concept of a solid biomass-fueled cogeneration plant operated under the regenerative Brayton cycle with an electrical power output of approximately 100 kW class, which addresses the typical energy needs in rural areas. The system comprises an air compressor, turbine, high-temperature heat exchanger (air preheater), combustion chamber and a utility heat exchanger (e.g. hot water heat exchanger). The high-temperature heat exchanger is a key component of the cycle, as it determines the maximum temperature of the generated flue gases, which translates into the efficiency of the system. Thus, the study carried out involves the analysis of a high-temperature heat exchanger performance and sizing in terms of a trade-off between maximizing system efficiency and technical constraints and cost-effectiveness. The thermodynamic calculations solve the system of thermodynamic and heat transfer equations for individual components, while utilising the RefProp database to determine variable properties of the fluids. The isentropic efficiencies of the compressor and the turbine are taken into account. The profitability of the system is examined and discussed through the analysis of economic indicators such as capital expenditure (CAPEX), operating expenses (OPEX) and the payback period. The study provides a basis for identifying operating and design conditions under which externally fired Brayton cycle units may become a viable solution for small-scale biomass-based cogeneration. The results of the study indicate that the payback period for the analyzed system configuration should not exceed 3 years.