An industrial biomass boiler of 200 kW thermal power is analyzed by computational and experimental methods. Gas composition and temperature within the furnace and in the downstream heat exchanger are measured. Combustion, flow and heat transfer processes within the furnace, exhaust tract as well as the forced convection on the water side of the heat exchanger are computationally investigated by the finite volume method-based computational fluid dynamics procedures. The predictions are compared with the experiments. A satisfactory overall agreement between the predicted and measured temperatures is observed with an average deviation about 5 %. For oxygen mole fractions a fair agreement is found that shows deviations within the range of 10-20 %. For carbon monoxide, calculations exhibit a stronger underprediction.