Plastic pipe and fittings can now be used for hot water supplies and central heating. They are easy to work with and allow the DIY plumber to tackle a wide range of jobs.
Over the last twenty years plastic has become the most popular plumbing material for above and below ground drainage, for rainwater collection and disposal, and for subsoil drainage. In the form of black polythene tubing it has also become a material widely used for water transportation on camping sites and farms. In the home, however, if has not proved popular. Although this lack of interest can partly be attributed to the conservatism of plumbers and householders, the main reason has been that up until now the plastic pipes that have been available have been suitable for cold water supplies only. This has meant that plumbers, who have had no choice but to use copper or some other metal for the pvc pipe sizes hot water or central heating system, have almost always tended to use the same material when dealing with the cold water system. Householders have doubted the ability of plastic pipework to do a good, life-long job, and have also tended to resist its use on grounds of taste. Quite simply, in places where pipework is exposed to view the combination of plastic and copper (or stainless steel or iron) is not one that is very pleasing to the eye.
The advantages of plastic pipework
The most obvious advantage is the lightness of the pipework, which makes for ease of handling, but the most important benefit is the ease with which plastic can be cut and joined. This means that the level of skill you require to undertake a particular plumbing task is greatly reduced, as is the amount of time you require to carry it out. Both systems are also strong and durable, more resistant to frost than a traditional plumbing system and, unlike the latter, not subject to corrosion. Last but not least, they are competitively priced.
Plastic pipes are less vulnerable to frost because plastic is a poor conductor of heat compared to metal (which means that, unlike metal, it provides a certain amount of insulation), and because it has greater elasticity. This means that plastic pipes are not only less likely to freeze than metal ones, but also that in the event of their doing so they are much less likely to burst. The greater degree of insulation that plastic provides also brings other benefits: it results in less heat being lost from pipe runs between radiators (or between the hot water cylinder and the hot taps), as well as meaning that less insulation is necessary for pipework that needs to be protected against the cold.
Plastic pipes aren't subject to corrosion for the simple reason that plastic isn't attacked by the water supply. Electrolytic corrosion, which results in the build up of hydrogen gas and black iron oxide sludge (magnetite) and can ultimately lead to leaky radiators and early pump failure, is therefore far less of a problem when a central heating system is fitted with plastic pipes.
This also means that plastic is a safer material to use for your drinking water supply pipes than metal, the use of which can, under some circumstances, present a health risk.
One final point to be borne in mind before you replace metal pipes with plastic ones is that plastic is a non-conductor of electricity. This means that all-plastic plumbing systems cannot be used to earth a domestic electricity supply.
You can obtain both polybutylene and CPVC tubing in the 15mm (½ inch), 22mm (¾ inch) and 28mm (1 inch) diameters commonly used in domestic hot and cold water supply and in small-bore central heating. However, in other respects - particularly as regards the flexibility of the two different typos of tubing and methods of cutting and jointing - the two systems differ. So, before you undertake a plumbing task using plastic pipes and fittings, you'd do well to consider which system best suits your particular application.