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Central Heating Plumbing

Depending on which type of central heating system you have chosen there are several factors which can influence how ‘green’ the plumbing is

  • Is the circuitry as compact as possible?
  • Is the circuitry zoned where necessary?
  • Is the pipework sized properly?
  • Is the pipework well insulated?
  • Will the materials be reusable or recyclable at the end of the building’s life?


Try to organize the pipework so as to avoid long wandering stretches of pipework which eat up pumping costs and risk losing heat on the way. Where possible a fairly central duct for services is the answer.

Pipework sizing

Virtually all central heating systems use a circulating pump and this pump is running all the time the boiler is on. Almost all circulating pumps have three settings (usually 40, 80 and 120 watts). The resistance of pipework to the flow of water depends on its length, the number of sharp bends and the diameter of the pipe. If you get these three factors optimised then most normal houses will work well on the 40 watt setting (or lower). This makes a large difference compared with the 120 watts which pumps often use. Plumbers are generally very aware of the first two factors – the length of runs and too many sharp bends and they try to minimize these problems. What very few of them know is that the resistance of pipework is inversely proportional to the fifth power of the diameter of the pipe. This means that a pipe with half the diameter has 32 times (2x2x2x2x2) more resistance. As an example a 15mm. pipe has more than 6 times the resistance of a 22mm. pipe This is why micro bore heating should normally be avoided and pipes be sized according to the size of radiators.

Pipework insulation

Make sure that hot pipework is insulated so that heat only goes to the area intended. The exception to this is pipework within the room that the pipes are feeding. In case you intend to create long runs of pipework (say to another house or outbuilding) then it is worth carefully calculating heat losses in the pipework. There is a free program for this called 3Eplus. It calculates the losses at a steady state so allowances need making for intermittency of use.


This relates to the choice of plastic plumbing or metal plumbing. Metal plumbing has an incredibly good record of being recycled (there’s many a plumber who makes his beer money solely from this). Whether plastic will follow suit is anyone’s guess. It should certainly be possible to do low grade recycling, as with other plastics but whether it will be reusable in its ‘original’ form depends on how consistent the manufacturers are about pipe and joint sizes and general specifications of fittings. In theory there is nothing to stop tube and fittings being reused several times (although there are already differing standards emerging whereby certain tubes don’t fit perfectly with certain fittings even when they appear to).

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