ABSTRACT
In low-temperature, hot water heating systems the boiler water temperature is thermostatically controlled to about 80°C. Systems may be open' with a small feed and expansion cistern or mains fed sealed' with an expansion vessel. High-level fan-assisted unit heaters are often the preferred means of heat emission for use with steam heating systems. A district heating system is in principle an enlarged system of heating one building, extended to heat several buildings. Modern boilers and heating systems are low water content to provide fuel efficiency and a rapid response. The schematic diagrams shown relate to a gravity or convected primary flow and return and pumped heating system and a fully pumped hot water and heating system using a three-way motorised valve. The name circulator as a component in domestic hot water and central heating systems is more realistic than pump, as the latter implies pressure of some intensity.
