Main components of a bagasse boiler are furnace, evaporator, superheater, boiler bank, economizer, and air heater. Combustion of fuel and air in the furnace produces thermal energy that is used to evaporate feed water in the evaporator. Hot flue gases from the furnace also contribute to increasing steam temperature in the superheater. Hot flue gases then pass through the boiler bank, resulting in additional water evaporation. After that, they pass successively through the economizer, in which feed water temperature is increased, and the air heater, in which air temperature is increased, before being exhausted to the atmosphere. It is known qualitatively that the boiler efficiency is increased with the heating surface area of each component. Quantitative effects of increasing heating surface areas, however, require a bagasse boiler model that takes into account their effects. The unavailability of a suitable model in the open literature is the main reason why this paper is written. The proposed model assumes the superheater is a radiative-convective heat exchanger, whereas boiler bank, economizer, and air heater are convective heat exchangers. The model is then used to determine how the boiler efficiency is affected by the heating surface areas of superheater, economizer, and air heater. It is found the boiler efficiency is most sensitive to change in economizer surface area.