hot water heating system

how water heating system

Domestic hot water (plumbers use the word ‘domestic’to distinguish it from the water in a radiator system) is usually a hot water heating system powered by at boiler. This may be free-standing in a kitchen or boiler house. mounted on e wall, or incorporated as a back boiler behind, say, a living room tire. Hot water for heating and domestic use is provided by the same boiler. For this hot water heating system, when the water has been heated it is stored in the hot cylinder, which may be housed in an airing cupboard. Various fuels can be used to power the boiler, including gas, solid fuel and oil. Electric boilers are also being introduced. Whatever fuel is used, it is a wise economy to maintain the temperature of the heated water, and to achieve this the hot cylinder should be well insulated. Special jackets are sold for this purpose. At one time a jacket 25 mm (1 in) thick was considered adequate, but with escalating fuel costs a thickness of 75mm or more is now the rule. If your cylinder has only a thin jacket, do not discard it, but place a new one on top of it. You cannot have too much insulation on a hot cylinder, and lower fuel bills will soon cover the cost of an insulation jacket. In normal circumstances, the hot water heating system will be of the gravity type, which works because hot water is lighter than cold.

Water heated in container will lie in layers of different temperatures, with the hottest at the top. So water heated by the boiler will rise to the hot cylinder through one pipe (the flow primary), and water that is cooler than this will fall to the boiler by another pipe (the return primary), to be heated in turn. For such hot water heating gravity system to work effectively, the hot cylinder must be sited at a higher level than the boiler, and indeed, in the average home it is customary for the boiler to be downstairs, with the hot cylinder in an airing cupboard conveniently by the bedrooms on the first floor. Even in bungalows and flats it is usually possible to raise the hot cylinder to a high enough level for the hot water heating gravity system to operate. For greatest efficiency, however, pumped primaries can be installed. Water from the cold tank (to replace the hot dravim off at the taps) is led into the system at the bottom of the hot cylinder, where it will quickly drop down to the boiler through the return primary, and be heated. The draw off point for water from the hot cylinder needs to be near its top, because that is where the water will be at its hottest. For modern hot water heating system, boilers are self regulating (thermostatically controlled) so they maintain the water at a required temperature without overheating. In case a regulating thermostat fails, however, overheated water would rise up a pipe (known as the vent pipe) from the top of the hot cylinder to the cold tank, and would discharge there harmlessly. Should the cold tank become overfull as a result, excess water would run away through the overflow.

solar-hot-water systemEven so, if you ever hear water boiling in the hot cylinder (something that used to be more common when thermostats were not so general), shut down the heating immediately and draw off hot water by opening a hot tap somewhere in the house. Then have the system serviced by a heating engineer. An immersion heater may be fitted to the cylinder, occasionally as a sole form of heating, but more usually as a standby if the boiler system fails. The hot cylinder may be either ‘direct’ or ‘indirect’. In a direct system the water heated in the boiler goes direct to the cylinder where it is stored until it is drawn off at the domestic taps. In an indirect system, water in a heating circuit is circulated through the boiler and a coil of piping within the cylinder. This coil serves as a heating element for the main body of water. Thus the water in the boiler and that for the taps are kept quite separate. Normally indirect cylinders are found where there is a radiator system of central heating, so in this hot water heating system, the domestic and radiator water are never mixed, but you do come across them where the boiler is used just for domestic hot water.

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