Boiler is a closed vessel that is used to produce steam at desired pressure.There is a reversal chamber for flue gases between 1st & 2nd pass is provided inside the boiler shell, Based on this reversal chamber boilers are differentiated into Wetback and Dry-back. In dryback boiler rear wall is lined with refractory. In dryback boiler reversal chamber has a rear wall that is lined with refractory, which passes combustion gasses from the furnace to multiple tube sheets and resulting in radiation losses.The dry back boiler design uses a common rear tube sheet and features convenient fire-side and water-side access. Dryback boilers also require regular refractory and tube sheet inspection, which can be costly maintenance items. Wetback boiler designs have a water gap between the furnace and back wall, Hence the radiation losses due to refractory lined reversal chamber in the back end smoke box are eliminated as the complete heat of the furnace is transferred to the water i