TUNDISH DISCHARGE
This is general information relating to the installation of discharge pipes for most boilers in the UK.
Discharge pipes must be left open to atmosphere, not blocking the tundish.
The responsibility for supplying and fitting the discharge pipe from the tundish is that of the certified
installer. In general, installation practice should be in accordance with the approved document G3 of
schedule 1 of the building regulations 1991, VIZ:
- (3.9) The discharge pipe from the tundish should terminate in a safe place where there is no risk to
persons in the vicinity of the discharge, be of metal and:
- (a) Be at least one pipe size larger than the nominal outlet size of the safety device unless its total
equivalent hydraulic resistance exceeds that of a straight pipe 9m long i.e discharge pipes between
9m and 18m equivalent resistance length should be at least larger than the nominal outlet size of
the safety device, between 18m and 27m at least 3 sizes larger, and so on. Bends must taken into
account in calculating the flow resistance. See Diagram below.
- (b) Have a vertical section of pipe at least 300mm long, below the tundish before any elbows or bends
in the pipework.
- (c) Be installed with a continuous fall.
- (d) Have discharges visible at both the tundish and the final point of discharge but where this is not possible or
practically difficult there should be clear visibility at one or other of these locations. Examples of acceptance
discharge arrangements are:
- (d.1) Ideally below a fixed grating and above the water seal in a trapped gully.
- (d.2) Downward discharges at a low level; i.e. up to 100mm above external surfaces such as car parks, hard
standings, grassed areas etc. are acceptable providing that where children may play or otherwise come
into contact with discharges, a wire cage or similar guard is positioned to prevent contact, whilst
maintaining visibility.
- (d.3) Discharges at high level; e.g. in to metal hopper and metal down pipe with the end of the discharge
pipe clearly visible (tundish visible or not) or onto a roof capable of withstanding high temperature
discharges of water and 3m from any plastic guttering systems that would collect such discharges
(tundish visible).
- (d.4) Where a single pipe serves number of discharges, such as in a block of flats, the number served should
be limited to not more than 6 systems so that any installation can be traced reasonably easily. The
single common discharge pipe should be at least one pipe size larger than the largest individual
discharge pipe to be connected. If unvented hot water storage systems are installed where discharges
from safety devices may not be apparent i.e. in dwellings occupied by blind, infirm or disabled people,
consideration should be given to the installation of an electronically operated device to warn when
discharge takes place.
NOTE: The discharge may consist of scalding water and steam. Asphalt, roofing felt and non-metallic
rainwater goods may be damaged by such discharges. However, there is seldom, if ever any discharge from Protherm Ray boilers.