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Plumbing - What you need to know . . .

This section will give advice on finding a plumber for your renovation project. It will also give a breakdown of plumbing services. These include:
  • Drainage (soil and waste water)
  • Domestic Hot and Cold Water Installation
  • Heating Sources (boilers, geo-thermal, biomass, etc.)
  • Heat Emitters (radiators, underfloor, etc.)

Water Installations

Water installations refer to methods of providing domestic water for both drinking and bathing to your home. There are two types of cold water and two types of hot water systems available. These are referred to as either direct or indirect systems.

Cold Water Installations

There are two types of cold water systems, direct and indirect.

Direct Cold Water System: The cold water is supplied to the outlets at mains pressure. The only storage requirement is a small capacity cistern to feed the hot water storage tank. The main advantage is that drinking water is available from all cold water outlets. Disadvantages include lack of reserve in case of supply cut off and a risk of reduced pressure during peak demand periods.

Indirect Cold Water System: This is much more common in domestic builds. Cold water is supplied to all outlets from a cold water storage cistern except for the cold water supply to the sink(s) where the drinking water tap is connected directly to incoming supply from the main. This system requires more pipework than the direct system but it reduces the risk of back syphonage and provides a reserve of water should the mains supply fail or is cut off.

Hot Water Installations

There are also two types of hot water systems, direct and indirect.

Direct Hot Water System: This is the simplest and least expensive system of hot water installation. The water is heated in the boiler and the hot water rises by convection to the hot water storage tank or cylinder to be replaced by the cooler water from the bottom of the storage vessel. Hot water drawn from the storage is replaced with cold water from the cold water storage cistern. Direct systems are suitable for soft water areas and for installations which are not supplying a central heating circuit.

Indirect Hot Water System: This is a more complex system than the direct system. This method is suitable for hard water areas and in all systems where a central heating circuit is to be part of the hot water installation. Basically the pipe layouts of the two systems are similar but in the indirect system a separate small capacity feed cistern is required to charge and top up the primary circuit.

With an Indirect Water system, the copper hot water cylinder contains a coil of pipe. This coil forms part of a run of pipework attached to the boiler. It is heated directly by the boiler. Indirectly, it heats the water in the cylinder. The coil, or "heat exchanger" forms part of the central heating circuit, and its water heating abilities are purely a by-product of its main function, which is to heat the radiators. This heating is called the "primary" circuit. The pipes running to and from the boiler are called the primary flow and return. The hot water tank operates in exactly the same way as the direct system.

Water Tanks: Cisterns

These are fixed containers used for storing water at atmospheric pressure.

The inflow of water is controlled by a floatvalve which is adjusted to shut off the water supply when it has reached the designed level within the cistern.

The capacity of the cistern depends on the draw off demand and whether the cistern feeds both hot and cold systems.

Domestic cold water cisterns should be placed at least 750mm away from an external wall or roof surface and in such a position that it can be easily accessed for inspection and cleaning.

An overflow or warning pipe of not less than 22mm diameter must be fitted to fall away to discharge in a conspicuous position.

Cisterns are available in a variety of sizes and materials such as moulded plastic and reinforced plastic. According to the Building regulations, the cold water storage cistern should have an actual capacity of not less than 212 litres in the case of a dwelling containing up to three bedrooms and an actual capacity of not less than 340 litres in the case of a dwelling containing four or more bedrooms.

If the cistern and its associated pipework are to be housed in a cold area such as a roof they should be insulated against freezing.

Water Tanks: Feed-and-Expansion tank

Conventional boiler systems operate with two water tanks in the loft: a large cold water tank and a smaller feed-and-expansion tank.

The large cold water tank draws water from the mains to feed the cylinder, which in turn is heated by the boiler.

The Feed-and-Expansion tank maintains the correct level of water in the heating system, and allows for the expansion of the water in the pipes and radiators when they get hot. It should be about 1/3 full so that it can accommodate the expanded water.

Normally, the water mains supply is connected to the F&E tank via a ball float valve arrangement, similar to the cistern. When the water level goes down the ball float will fall allowing cold water flow in and fill the tank. As water flow in, float will rise. When the pre-set level is reached the ball valve will close stopping the water supply.

Water Tanks: Hot Water Cylinders

There are three types of hot water cylinders. These are vented direct and indirect cylinders and unvented cylinders.

1) Direct Cylinder: With a direct cylinder the water is heated directly via an electric immersion element, or from a remote heating boiler, which has been designed for water heating only, for example a copper coal fired back boiler.
This is the simplest form of water heating, it gets its name from the fact that the water drawn from the hot taps has been directly heated via the boiler, i.e. the stored water has been through the copper back boiler or around the immersion coil and is then used for bathing.

2) Indirect Cylinder: With an indirect water heating system and cylinder, the water that circulates around the boiler, pipes and radiators is kept totally separate from the stored water in the cylinder that is used for bathing.
Heating system components are generally made of a mixture of metals including iron and steel. Oxygen and water are very corrosive and heating systems need to be protected with chemicals to reduce the threat of corrosion. The water for bathing is kept separate from the heating system water by use of an indirect heating coil or heat exchanger.

3) Unvented Cylinder: The unvented system operates purely from mains water. Unvented cylinders provide mains pressure hot water to taps and showers. These are very different from conventional hot water cylinders. Conventional cylinders are not pressurized and must be fed from a cold water tank.
Many safety devices are built into this system to accommodate for the greater pressure and expansion of the water. Although a small tank may be found in the loft for venting and feeding your central heating, no cold water storage tank is necessary.