Heatrae Sadia Multipoint ECO 30L V 3kW Installation, Operation And Maintenance Manual page 12

Discharge
It is a requirement of Building Regulation G3 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 Regulation G3. The G3
Requirements and Guidance section 3.50 - 3.63 are
reproduced in the following sections of this manual.
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/pressure relief valve) must be installed in
a continuously downward direction and in a frost free
environment.
Water may drip from the discharge pipe of the pressure
relief device. This pipe must be left open to the
atmosphere. The temperature/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."
The following extract is taken from the latest G3
Regulations
Discharge pipes from safety devices
Discharge pipe D1
3.50 Each of the temperature relief valves or combined
temperature and pressure relief valves specified in
3.13 or 3.17 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 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 the 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
water heater 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,
12
the valve, with no more than 600mm of pipe between
the valve outlet and the tundish (see Fig 7).
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 Fig. 7); and
(b) be installed with a continuous fall thereafter of at
least 1 in 200.
3.57 The discharge pipe (D2) should be made of:
(a) metal; or
(b) other material that has been demonstrated to be
capable of safely withstanding temperatures of the water
discharged and is clearly and permanently marked to
identify the product and performance standard (e.g. as
specified in the relevant part of BS 7291).
3.58 The discharge pipe (D2) should 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. for discharge
pipes between 9m and 18m the equivalent resistance
length should be at least two sizes larger than the
nominal outlet size of the safety device; between 18
and 27m at least 3 sizes larger, and so on; bends must
be taken into account in calculating the flow resistance.
See Fig 11, Table 3 and the worked example.
Note: An alternative approach for sizing discharge
pipes would be to follow Annex D, section D.2 of BS
6700:2006 Specification for design, installation, testing
and maintenance of services supplying water for
domestic use within buildings and their curtilages.
3.59 Where a single common discharge pipe serves
more than one system, it should be at least one pipe
size larger than the largest individual discharge pipe
(D2) to be connected.
3.60 The discharge pipe should not be connected to a
soil discharge stack unless it can be demonstrated that
the soil discharge stack is capable of safely withstanding
temperatures of the water discharged, in which case, it
should:
(a) contain a mechanical seal, not incorporating a
water trap, which allows water into the branch pipe
without allowing foul air from the drain to be ventilated