Hot water boilers are tanks that transfer heat to water that is circulated for heating purposes. They are made of stainless steel, cast iron, aluminum, and steel and are capable of withstanding increased temperature and pressure. The hot water boilers can running under atmospheric pressure or bearing pressure. Hot water boilers are used widely in residential, commercial and institutional buildings, green house, swimming pool, hospital, department central heating, hotel central heating, laundry, and industrial process.