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.
Central Heating Systems
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.
Boilers
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.
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