"Furnaces@ as used in a refinery@ are more commonly known as ""fired heaters@ ""fired pipe stills@"" ""heaters@ or ""gas generators."" This chapter covers the inspection of fired heaters and stacks. It includes a description of the various types of fired heaters and stacks and discusses the reasons for inspection@ causes of deterioration@ frequency and methods of inspection@ methods of repair@ and records and reports. Safety and efficiency of operation are emphasized. In this chapter@ the term operating conditions is used to mean the combination of pressure@ temperature@ and velocity of the fluid being heated@ as well as the muffle temperature and the composition of combustion products in the heater or piece of equipment under discussion."