Now a days in industry major losses are find out so here we calculate these losses and find out efficiency of boiler. Boiler efficiency and energy losses from boiler are important parameter for any industry using boiler. In this work a detailed analysis was carried out for boiler at Anish Chemicals Bhavnagar. It is a combined water and fire tube boiler using biomass coal as fuel. Boiler efficiency calculated by direct method is in range of (78.5% to 81.6%). Major losses from boiler are heat loss due to radiation and convection from uninsulated surfaces (4.8% to 6.3%), heat loss due to flue gas (6.3% to 6.4%), heat loss due to blow down (0.263 to 0.398%), heat loss due to incomplete combustion (1.87% to 2.21%), heat loss due to unburnt coal in bottom ash(1.74 % to 1.86 )and heat loss due to moisture present in fuel (1.3% to 1.6%).To reduce radiative and convective heat loss from flue gas duct surface, flexible glass mineral wool insulation was suggested.