Combined heat and power production in houses is a long-term sustainable option which, in the case of isolated rural areas with low insolation, can be supplied with biomass collected from clearing nearby forests and crops. In this context, the integration of a biomass boiler with a Stirling engine allows the operation of the boiler as long as the engine has a limited power output. This is the case of the model being developed for a pyrotubular biomass condensing boiler with a thermal power of 25 kWt, coupled to a Free Piston Stirling engine (FPSE), whose nominal power is one kWe and consumes around four kWt of the thermal power of the boiler. The model results have been validated with data from both the boiler and the FPSE manufacturers, as a preliminary part of the installation being set up in the university facilities. The model allows the partial load of the boiler and the fuel composition to be modified, thus estimating both the boiler efficiency and the derived electrical output. The results show that this scheme can be an excellent complement to PV-batteries installations in rural dwellings by providing electricity and heat in winter, when solar contribution is low, with appropriate management of the number of hours of operation, prioritising the maximum load at times of greatest thermal demand.