WATER PIPE BOILERS AND API PIPE BOILERS Classification of boilers in general are grouped into 2, namely: 1. Fire Pipe Boilers 2. Water Pipe Boilers Fire Pipe Boilers In the type of fire pipe boilers heat transfer from hot gas to water then the water turns into steam, this is due to the hot gas produced by combustion ( flue gas) flows through pipes that are covered with water on the ...