Hot water heating systems and supplies include hydronic heaters and steam boilers, along with components to help ensure proper heater function. Hydronic heaters use heated liquid to control the temperature in a room or area, such as a garage, shop, sports facility, or school gym. Steam boilers include high-efficiency wall-mounted condensing boilers, cast-iron compact gas-fired boilers, and direct-spark boilers. They create heat by pumping hot water or steam through heat exchangers at various points along the heating system.