Losses in Steam Boiler Dry Flue Gas Losses (Stack losses) H2 Losses Moisture in Fuel Moisture in Air CO Losses Surface Losses – Due to Poor Insulation Fly Ash Losses – Heat Carried by Fly Ash Bottom Losses (Unburnt Losses) OTHER LOSSES Losses due to poor Smoke side Boiler sealing. Losses due to Steam leakages. Blow-down loss. Losses due to the part load operation.