Cast iron radiators are used in hydronic (hot water) and steam heating systems. They transmit heat by both convection and radiation heat transmission. Air contacting the heated iron surfaces becomes heated through convection, then circulating through the room. Warmed air radiates out into the room air as well. Most modern radiators use hot water
Radiator modules are constructed by joining together a series of hollow vertical sections, each section having a waterway opening at the top and bottom. Metal round fittings and gaskets are attached to the openings to form passages, through which hot water or steam flows. The number of section used varies depending on the size of the space to be heated and configuration of the room, window placement, etc.