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6.10 Discharge Pipework
The following is an extract from Section G3 of the Building Regulations for England and Wales
and provides guidance on the requirements for discharge pipework. Refer also to Diagram 1.
This information is correct at time of publication of this manual. For other regions, please refer to
local guidance.
Discharge pipe D1
3.50 Safety devices such as temperature relief valves or combined temperature and pressure
relief valves (see paragraphs 3.13 or 3.18) should discharge either directly or by way of a
manifold via a short length of metal pipe (D1) to a tundish.
3.51 The diameter of discharge pipe (D1) should be not less than the nominal outlet size of the
safety device, e.g. temperature relief valve.
3.52 Where a manifold is used it should be sized to accept and discharge the total discharge from
the discharge pipes connected to it.
3.53 Where valves other than a temperature and pressure relief valve from a single unvented
hot water system discharge by way of the same manifold that is used by the safety devices, the
manifold should be factory fitted as part of the hot water storage system unit or package.
Tundish
3.54 The tundish should be vertical, located in the same space as the unvented hot water
storage system and be fitted as close as possible to, and lower than, the safety device, with no
more than 600mm of pipe between the valve outlet and the tundish (see Diagram 1).
Note: To comply with the Water Supply (Water Fittings) Regulations, the tundish should
incorporate a suitable air gap.
3.55 Any discharge should be visible at the tundish. In addition, where discharges from safety
devices may not be apparent, e.g. in dwellings occupied by people with impaired vision or mobility,
consideration should be given to the installation of a suitable safety device to warn when
discharge takes place, e.g. electronically operated.
Discharge pipe D2
3.56 The discharge pipe (D2) from the tundish should:
a. have a vertical section of pipe at least 300mm long below the tundish before any elbows or
bends in the pipework (see Diagram 1); and
b. be installed with a continuous fall of at least 1 in 200 thereafter.