Waste heat is generated in a process by the way of fuel combustion or chemical reaction, and then dumped into the environment. Even though, it could still be reused for some useful and economic purpose. A large quantity of hot flue gases is generated from boilers, furnaces, IC engines, etc. If some of this waste heat could be recovered, a considerable amount of primary fuel could be saved. The energy lost in waste gases cannot be fully recovered. However, much of the heat could be recovered and losses could be minimized by adopting certain measures like EGR and vapour absorption system.