Discharge Pipework; G3 Requirement; Schematic Discharge Pipe Arrangement - MEGAFLO Eco Product Manual

Discharge Pipework

It is a requirement of Building Regulations that any discharge from an unvented system is conveyed to where it is visible, but will not cause danger
to persons in or about the building. The tundish and discharge pipes should be fitted in accordance with the requirements and guidance notes of
Building Regulations. Building Regulation G3 Requirements and Guidance (p. 17) are reproduced in the following sections.
For discharge pipe arrangements not covered by G3 Guidance advice should be sought from your local Building Control Officer. Any discharge pipe
connected to the Pressure Relief devices (Expansion Valve and Temperature and Pressure Relief Valve) must be installed in a continuously downward
direction and in a frost free environment.
The water may drip from the discharge pipe of the Pressure Relief device and that this pipe must be left open to the atmosphere. The Pressure Relief
device is to be operated regularly to remove lime deposits and to verify that it is not blocked.

G3 Requirement

"...there shall be precautions...to ensure that the hot water discharged from safety devices is safely conveyed to where it is visible but will not cause
danger to persons in or about the building".
Notes:
1) Discharge pipe-work D2 can now be a plastic pipe but only pipes that have been tested to a
minimum110°C must be used.
2) Discharge pipe D2 can now be plumbed in the soil stack but only soil stacks that can handle
temperatures of 99°C or greater should be used.
Table 5 Sizing of copper discharge pipe "D2" for common T&P Relief Valve sizes.
VALVE OUTLET
SIZE
G 1/2
G 3/4
G 1
Figure 10 - Schematic discharge pipe arrangement
18
Unvented Hot Water Cylinder
MINIMUM SIZE OF MINIMUM SIZE OF
DISCHARGE PIPE D1 DISCHARGE PIPE D2
FROM TUNDISH
15mm 22mm
28mm
35mm
22mm 28mm
35mm
42mm
28mm 35mm
42mm
54mm
Safety device
(e.g. Temperature
relief valve)
Metal discharge pipe (D1) from
Temperature relief valve to tundish
600mm maximum
300mm
minimum
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulation G3 section 3.56,
Table 4 and worked example
RESISTANCE CREATED BY
MAXIMUM RESISTANCE
EACH ELBOW OR BEND
ALLOWED, EXPRESSED
AS A LENGTH OF
STRAIGHT PIPE (I.E. NO
ELBOWS OR BENDS
UP TO 9m 0.8m
UP TO 18m 1.0m
UP TO 27m 1.4m
UP TO 9m 1.0m
UP TO 18m 1.4m
UP TO 27m 1.7m
UP TO 9m 1.4m
UP TO 18m 1.7m
UP TO 27m 2.3m
Tundish
Discharge below
fixed grating
(Building Regulation
G3 section 3.61 gives
alternative points
of discharge)
Fixed grating
Trapped
gully