Evaluation of Plastics Tubing for Domestic Wet Central Heating

British Gas has an interest in alternative pipework materials for wet central heating systems, and has been studying candidates, including a number of plastics, for more than 10 years. Performance requirements are outlined. A significant aspect is that of compatibility with other components of the system, and a novel experiment to study this problem is described.

Over the past 20 or more years, wet central heating has become increasingly popular in this country. The most common type, which is peculiarly British, has copper pipework, mild steel panel radiators, a gas, solid fuel, or oil fired boiler and a small feed/expansion tank. Typical conditions are a water temperature of up to 90°C and a head of 2-3 bar.
Copper is overwhelmingly the most commonly used pipework material, and has many advantages.
A tendency to unpredictable price and availability fluctuations does, however, mean that the long term picture is not so clear.
Over the last 10 years or so, a number of plastics manufacturers, seeking to expand from already established markets in waste water disposal and cold water supply, have developed pipework systems which may be suitable for this application. As British Gas has a very large interest in the installation and servicing of wet central heating systems it is necessary for us to be aware of possible alternatives to copper for this most arduous of domestic plumbing applications, and to evaluate the most promising candidates.
In this paper, we outline briefly the performance required in domestic wet central heating, and how it may be shown that a particular plastics system can achieve this performance.

One aspect is the question of compatibility with other materials in the system; neither the plastics pipework nor the metal components of the system should accelerate the degradation of the other. A novel experiment we have carried out to examine this potential problem is described. It concentrates on the risk of increased corrosion of mild steel radiators by agents either released from, or allowed into the system by, plastics tubing materials.