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Appendix
A.2
A
84
Alternative Discharge
Discharge pipes should be in metal and dedicated to the unvented cylinder. The pipe should
have a continuous fall and should terminate in a safe and visible place. Downward discharges at
low level, i.e. up to 100 mm 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.
Discharge at high level, i.e. into a metal hopper and metal down pipe with the end of the dis-
charge pipe clearly visible (tundish visible or not) or onto a roof capable of withstanding high
temperature discharges of water and 3 m from any plastics guttering system that would collect
such discharges (tundish visible).
Where a single pipe serves a number of discharges, such as in blocks of flats, the number
served should be limited to not more than 6 systems so that any installation discharging 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. For further information contact
your Building Control Office.
Safety device
(e.g. temperature
relief valve)
Discharge pipe (D2) from tundish,
with continuous fall.
Valve
Minimum size of
outlet size
discharge pipe D1*
G1/2
15 mm
G3/4
22 mm
G1
28 mm
Metal discharge pipe (D1) from
temperature relief valve to tundish
Tundish
300mm
minimum
Minimum size of
discharge pipe D2*
from tundish
22 mm
28 mm
35 mm
28 mm
35 mm
42 mm
35 mm
42 mm
54 mm
Discharge below
fixed grating
(3.61 gives
alternative points
of discharge)
Fixed grating
Maximum resistance
allowed, expressed as
a length of straight pipe
(i.e. no elbows or bends)
up to 9 m
up to 18 m
up to 27 m
up to 9 m
up to 18 m
up to 27 m
up to 9 m
up to 18 m
up to 27 m
DHW PAW-VP - Installation manual – 2020-05
Trapped gulley
Resistance
created by
each elbow or
bend
0.8 m
1.0 m
1.4 m
1.0 m
1.4 m
1.7 m
1.4 m
1.7 m
2.3 m
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