Traditionally houses were all plumbed in the same way: Straight lengths of copper pipe were bent into shape with pipe-bending springs, and then connected together with soldered copper fittings or brass compression fittings. For a long time nothing changed, but in recent years a new concept has grown up, with increased use of plastic plumbing fittings. Although plastic in plumbing is nothing new, it tended to be used as uPVC waste fittings, where there is no significant water pressure, or in polyethylene supply pipe which is relatively thick walled and inflexible making it unsuitable for indoor use. That has all changed with the availability of rigid cross-linked polyethylene (PE-X) pipe which is capable of withstanding the high pressure of mains supplied water, while still being flexible. Its availability in lengths of up to 150 metres obviates the need for joints every two or three meters allowing long runs to be made quickly and easily. To complement the plastic pipe, plastic connectors were introduced which are not only compatible with copper pipe but are push-fit - no tools are required to make the joint and they are easily demountable, some makes by hand, some requiring a release tool. Although building tends to be a conservative industry, plastic fittings and pipework can now be found in new dwellings built by many of the major construction companies.

Plastic plumbing can be used for both hot and cold water supplies, and for central heating systems. There are only four caveats for this type of pipework:

• The first meter of pipework from the boiler must be in copper
• The higher the temperature of the water being carried, the lower the maximum allowable water pressure must be
• Where joints are made, manufacturers will specify the use of a pipe-insert to make the pipe end rigid. Without these there is the possibility that the pipe could deform and allow the joint to leak or fail.
• Plastic pipework must not be used for gas supplies due to the danger factor in case of a house fire.

The most commonly installed central heating system in the UK today consists of a gas or oil fired boiler used to heat water which is pumped via a network of pipes to double-skinned, pressed-metal panel radiators in each room of the building. Such systems have proven to be reliable, efficient and relatively easy to retro-fit to existing buildings. In recent years the alternative system of underfloor heating has emerged, primarily aimed at new builds . With the increasing availability of plastic plumbing, efficient insulation and multi-zone controllers, underfloor heating has become a viable and affordable means of heating your home and can offer the advantage of far more even heating throughout a room than is possible with radiators.

Underfloor heating can be fitted to any type of floor, either buried in the screed of a solid floor or held against the wood of a suspended floor. In both cases a layer of insulation is immediately below the pipe work to ensure the heat is directed into the living area and not wasted. The pipes run to a multi-valve manifold which, in conjunction with electronic room stats, convert the entire heated area into separately controllable zones. This allows greater flexibility for the user and aids efficiency as unused rooms can be easily switched out of the system..

As with the choice of central heating system you choose there are decisions to be made about the boiler that will run it. Any boiler will support any type of wet heating system, but how it provides domestic hot water (DHW) will determine the type required. The decision is either instantaneous (or combi), or stored. The stored system is the most familiar with the boiler used to heat the water in a lagged copper cylinder which is then drawn off as required. Both the pressure of the DHW and the replenishment of the tank is provided from a large cold water tank in the loft that feeds the cylinder. The boiler does not heat the water directly in this system, instead relying on a coiled heating element in the tank which keeps the anti-corrosion treated heating water separate from the stored hot water .

With an instantaneous system the boiler is used to heat the DHW on demand by use of flow switches to detect when a hot tap is running and large, efficient heat exchangers to warm the water. The main selling point of such systems is the potentially huge savings that can be made against a system that heats water that may not be used. Such a system also does away with the need for space for the cylinder and the loft header tank, and provides the hot water at mains pressure. However, while these advantages may seem to ring the death knell for any other type of system, it must be remembered that the amount of hot water that the boiler can provide at any given time is limited and is inversely proportional to the incoming water temperature; the greater the temperature rise needed the more the boiler has to reduce the flow. If the system is to be installed in a house with many bathrooms, or with one of the modern showering systems that require large flow rates of hot water, then a combi boiler may not be able to cope adequately.

As already mentioned, one of the advantages of a combi system is mains pressure hot water which, traditionally, has not been available with a stored DHW system. In the traditional system, also known as a gravity system, the water pressure available is provided entirely by the height difference between the loft tank and the tap, and is seldom very high. A typical 5 metre head provides a pressure of 0.5 bar (7.4psi), while the incoming mains pressure can be up to 10bar (147psi). Although good flow rates can be more important than high pressure, modern mixer taps and high flow shower units which are often designed for Europe where combi systems are the norm, often require matched pressures to function properly. To this end it is now possible to have an unvented cylinder. This is effectively a reinforced hot water cylinder capable of withstanding several bars water pressure. The plumbing for these types of cylinder will be more complicated than a traditional cylinder as there have to be pressure release valves, an expansion vessel and a pressure regulating valve - but one tank can provide for any number of showers and taps at flow rates restricted only by the pipework and the incoming water flow. If you opt for an unvented cylinder it must comply with both Water Regulations and Building Regulations.

Since unvented cylinders must be fitted with several safety devices, lists of competent fitters are registered with the Institute of Plumbing, the Construction Industry Training Board or the Association of Installers of Unvented Hot Water Systems (Scotland and Northern Ireland.) These systems should be regularly serviced to ensure they remain in good working order.

Finally, and most obviously, there is the question of whether the boiler is oil, gas or solid fuel fired. This is often chiefly dictated by whether gas is available on site, or not, as the case may be and most people will tend to opt for connection to the gas supply if it is available as this obviates any need for dealing with fuel deliveries.

IMPORTANT NOTE: As always, any tradesman working on gas pipework or appliances on the consumer side of the meter must be individually CORGI registered. CORGI registration ensures proper training in both the theoretical and practical aspects of gas-fitting. Although plumbing for gas is very similar to water - both use copper pipe and soldered fittings - the design of gas pipework is more technically involved than often realised; for example gas pipework must be sized according to the demand of the appliances fitted as well as the length of run involved so that there is less than a 1 millibar pressure loss between the gas meter and each appliance. The practical aspects cover installation safety - for example not running pipework unsheathed in a cavity wall - and the correct way to conduct pressure testing of the installation.

If mains gas is not available then one can choose to have the system powered by either Heating Oil, Liquid Petroleum Gas (LPG.) or by solid fuel. Both oil and gas solutions will require storage tanks that are positioned so that they can be accessed and refilled by fuel tankers. The fuel companies will often specifying the furthest they are willing to trail their supply pipes and it is worth finding this out in advance when planning where to put your tank. If the tank has to be further than they will allow, then extra fixed pipework can be added to provide a remote filling point. The choice of oil, gas or solid fuel is a personal preference, usually based on the current and predicted prices of the commodity, and on the handling considerations. A side benefit of LPG on sites where mains gas in not available is that a suitable gas hob can be connected and used in the kitchen. Gas hobs are often preferred by cooks, to most electric hobs, as they heat faster and give quicker response times when turning down a pan that's boiling over.

Apart from any conditions of access to an oil tank, you are pretty well free to put one anywhere on your property. Normally oil tanks are simply tough single skinned polyurethane containers but if there is a danger that, if it were punctured, pollution of any nearby streams or waterways in its vicinity could occur then it must be 'bunded'. A bunded oil tank is, put simply, double skinned and your BCO can determine whether one is required or not. Many companies however will fit bunded tanks as standard as it also safeguards against general environmental damage and, with the seemingly ever increasing price of oil, financial loss in case of damage to the tank. Buildbase supply the Titan range of Oil Storage tanks - details can be found at http://www.environmental-containers.com.

Since mid-2005 all new gas-fired boilers in the UK have had to reach certain standards in their levels of efficiency to meet regulations. They have to be SEBDUK A-rated and to reach this level have to be of a type known as 'condensing'. Normally the moisture generated by combustion in a boiler exits the flue as steam but with a condensing boiler even more energy is extracted from the combustion process, usually by means of a second heat exchanger, and this results in the moisture condensing inside the boiler which has then to be disposed of by means of a small pipe, usually draining to the outside world.

Oil fired boilers are currently exempt from this legislation until mid-2007 when similar rules will be applied.