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Some facts about water heating
Circulating hot water can be used for central heating. Sometimes these systems are called hydronic heating systems.15
Common components of a central heating system using water-circulation include:
A supply of fuel, electric power or district heating supply lines
A Boiler (or a heat exchanger for district heating) which heats water in the system
Pump to circulate the water
Radiators which are wall-mounted panels through which the heated water passes in order to release heat into rooms.
The circulating water systems use a closed loop; the same water is heated and then reheated. A sealed system provides a form of central heating in which the water used for heating circulates independently of the building's normal water supply.
An expansion tank contains compressed gas, separated from the sealed-system water by a diaphragm. This allows for normal variations of pressure in the system. A safety valve allows water to escape from the system when pressure becomes too high, and a valve can open to replenish water from the normal water supply if the pressure drops too low. Sealed systems offer an alternative to open-vent systems, in which steam can escape from the system, and gets replaced from the building's water supply via a feed and central storage system.
Heating systems in the United Kingdom and in other parts of Europe commonly combine the needs of space heating with domestic hot-water heating. These systems occur less commonly in the USA. In this case, the heated water in a sealed system flows through a heat exchanger in a hot-water tank or hot-water cylinder where it heats water from the regular potable water supply for use at hot-water taps or appliances such as washing machines or dishwashers.
A boiler is a closed vessel in which water or other fluid is heated. The fluid does not necessarily boil. (In North America the term "furnace" is normally used if the purpose is not actually to boil the fluid.) The heated or vaporized fluid exits the boiler for use in various processes or heating applications,12 including water heating, central heating, boiler-based power generation, cooking, and sanitation.
History of bathtub
Documented early plumbing systems for bathing go back as far as around 3300 BC with the discovery of copper water pipes beneath a palace in the Indus Valley Civilization of ancient India; see sanitation of the Indus Valley Civilization. Evidence of the earliest surviving personal sized bath tub was found on the Isle of Crete where a 1.5-metre (5 ft) long pedestal tub was found built from hardened pottery.
The clawfoot tub, which reached the apex of its popularity in the late 19th century; had its origins in the mid 18th century, where the ball and claw design originated in Holland, possibly artistically inspired by the Chinese motif of a dragon holding a precious stone. The design spread to England where it found much popularity among the aristocracy, just as bathing was becoming increasingly fashionable. Early bathtubs in England tended to be made of cast iron, or even tin and copper with a face of paint applied that tended to peel with time.1
The Scottish-born inventor David Buick invented a process for bonding porcelain enamel to cast iron in the 1880s while working for the Alexander Manufacturing Company in Detroit. The company, as well as others including Kohler Company and J. L. Mott Iron Works, began successfully marketing porcelain enameled cast-iron bathtubs, a process that remains broadly the same to this day. Far from the ornate feet and luxury most associated with clawfoot tubs, an early Kohler example was advertised as a "horse trough/hog scalder, when furnished with four legs will serve as a bathtub." The item's use as hog scalder was considered a more important marketing point than its ability to function as a bathtub.1
In the latter half of the 20th century, the once popular clawfoot tub morphed into a built-in tub with a small apron front. This enclosed style afforded easier maintenance and, with the emergence of colored sanitary ware, more design options for the homeowner. The Crane Company introduced colored bathroom fixtures to the US market in 1928,citation needed and slowly this influx of design options and easier cleaning and care led to the near demise of clawfoot-style tubs.