In most cases, domestic hot water is supplied from a storage cylinder, the water being heated by a boiler or electric heating elements in the cylinder itself. Over a period of time, the cylinder may no longer meet your needs for a variety of reasons: it may have become corroded and begun to leak; it may have insufficient capacity for a growing family’s needs; you may prefer to fit a modern, properly insulated version in place of an unlagged type; or you may be changing the hot water system from direct to indirect, or vice versa.
Whatever the reason for installing a new cylinder, it may be a useful exercise at this time to assess if the hot water system performs as well as you require. If it does not, you can take the opportunity of installing a cylinder system of improved performance (mains pressure, for example), and remove the cold water cistern from the loft.
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| Hot Water Supplies |
The Surrey flange
A device designed to draw off hot water from a relatively air-free position, just below the top of the hot water cylinder, is known as the Surrey flange. Hot water supply to the shower, or for any other critical use, comes via a centrally-mounted draw-off tube, which is offset to one side of the main outlet from the cylinder. The flange allows trapped air and water vapour to vent from the cylinder through the expansion pipe, and not to be dragged into the shower supply, where it could disrupt thermostatic control, etc.
Another advantage is that the position of the inlet helps to maintain flow, and hence shower water temperature when other hot outlets are also being used.
The flange simply fits into the top outlet of the hot water cylinder. With the water drained to below the cylinder head, all that is necessary is to remove the top connection, insert the flange, and reconnect the pipe. No special tools are required other than the correct spanners.
Immersion heaters
Immersion heaters perform two roles in the supply of hot water. They can either be used as a supplementary source of cylinder water heating when the main boiler is not required, or they can be the only form of storage water
heating, taking advantage of reduced electricity tariffs. In the supplementary role, normally only one immersion heater (either single- or dual-element) is fitted to the cylinder. When used as the primary source of heat, however, two or more horizontal immersion heaters are installed. The lower element is normally wired up to operate during off-peak tariff times, while the upper heater is wired for peak-rate top-up duties during the day.
Long, single or dual elements may be mounted to the top of the cylinder, while short, single elements are likely to be mounted horizontally near the base. Since only the water above the lowest point of the element will be heated, it is important that any heater projecting down from the top is of the correct length to heat the whole cylinder. Also, it must not foul either the heating coil or any corrosion-inhibiting anode fitted within the cylinder.
Dual elements may also be wired for off-peak heating, the long element for off-peak tariffs, and the shorter element for peak daytime use. Separate wires from the control switches should be used for each heater.
Each immersion heater must be fitted with a thermostat, which should be set at 60°C. This temperature provides water that is hot enough for domestic use without the danger of excessive scale formation in hard water areas.
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