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26. WATER CONNECTIONS Heating systems
The size of the heating system, which can be run, will depend on the output rating of the appliance. It will be
necessary to work out heat loss calculations for the system envisaged in order to establish the kW/hr rating. An
appliance that will meet this figure can then be chosen; (for boiler outputs please refer to the brochure).
The constructional requirements of installing and connecting the appliance also need to be taken into account
when selecting. Design and calculations for individual heating systems should be carried out by a qualified
heating engineer. In many cases your supplier will be able to offer advice and assistance.
Direct systems
Stainless steel boilers, either factory fitted or retro-fitted as add-in boilers enable connection to direct systems to
be made without the need to change the cylinder or to fit an expansion tank. This applies to domestic water
supply only and should not be done when in an area with soft water. If radiators are used then an indirect
system must be utilised.
To connect the cylinder use 28mm copper pipes.
Ensure that the pipes rise continuously to the cylinder.
Ensure that the runs are not too long, i.e. 6.1m (20ft) maximum each for flow and return.
Install the cylinder above the level of the fire, and as close to it as possible. (the higher the cylinder the faster the
circulation).
Ensure that no valves are present in the circulating pipes.
Indirect systems - The Domestic Hot Water Circuit
In addition to providing hot water the primary circuit is essential in providing a "heat leak" to absorb excessive
heat produced in the event of the circulation pump shutting down.
Heat is produced in varying quantities while the fire is alight and care must be taken to ensure that effective
circulation can occur around the primary circuit to carry heat away and thus stop boiling. The output of any
radiator installed as a "heat leak" should not be less than 10% of the rated output of the appliance. The radiator
should not be fitted with a control valve.
The cylinder must be of the indirect type with a minimum capacity of 110 litres, conforming to BS 1566 part 1.
Primary flow and return pipes should be 28mm diameter. The cylinder should be installed at a higher level than
the appliance, and as close to it as possible (the higher the cylinder the faster the circulation). The flow and
return pipes should not be longer than 6.1m (20ft) each. Pipe runs should rise continually from the boiler to the
cylinder. A radiator of approximately 25 sq.ft. should be connected into the primary circuit, if installed in the
bathroom it provides a means of dying towels in the summer.
Safety vent circuit
This circuit consists of a cold feed pipe, expansion pipe, and expansion tank. The possibility that water may boil
can never be completely ruled out, and it is therefore vital to ensure that cold water can be supplied to the boiler
and steam vented from it at all times.
The expansion tank should have a capacity of at least 7 % of the system's water capacity.
The cold water feed pipe should be at least 22mm diameter.
There must not be any shut off valves in the circuit.
Pipes should be run to avoid air locks.
A spring safety valve should be fitted to the expansion pipe close to the boiler.
It is often possible, and is good practice, to utilise the primary flow and return as part of the safety circuit.
The ball valve should have a copper ball.
The overflow pipe from the expansion tank should be 28mm diameter copper.
Pipes in unheated spaces must be lagged.
Before handing over the installation to the customer it is strongly recommended that the appliance is lit and the
functioning of the chimney, hot water and heating system is checked.