16
5 Domestic Hot Water
Diagram 5.2
12529
NOTE: The discharge will consist of scalding water and
steam. Asphalt, roofing felt and non-metallic rain water
goods may be damaged by such discharges.
Worked example of discharge pipe sizing
The example given in diagram 5.2 is for a G1/2 temperature
relief valve with a discharge pipe (D2) having 4 No. 22mm
elbows and length of 7m from the tundish to the point of
discharge.
From Table 1:
Maximum resistance allowed for a straight length of 22mm
copper discharge pipe (D2) from a G1/2 temperature relief
valve is 9.0m.
Subtract the resistance for 4 No. 22mm elbows at 0.8m
each = 3.2m.
Therefore the permitted length equates to 5.8m.
5.8m is less than the actual length of 7m therefore calculate
the next largest size. Maximum resistance allowed for a
straight length of 28mm pipe (D2 from a G1/2 temperature
relief valves equates to 18m. Subtract the resistance of 4
No. 28mm elbows at 1.0m each: 4.0m.
Therefore the maximum permitted length equates to: 14m.
As the actual length is 7m a 28mm min (D2) copper pipe will
be satisfactory.
WARNING:
• Under no circumstances should the factory fitted
temperature/pressure relief valve be removed other than
by authorised personnel. To do so will invalidate any
warranty claim.
• Table 1. Sizing of copper discharge pipe (D2).
• Control and safety valves MUST NOT be tampered with.
• The discharge pipe MUST NOT be blocked or used for
any other purpose.
• The tundish is factory fitted and MUST NOT be
removed.
13449
Discharge pipe D2
from tundish
Resistance created by
each elbow or bend
Maximum resistance
allowed, expressed
as a length of straight
pipe (i.e. no elbow or bends)
Discharge pipe D1
Valve outlet
size
15mm
22mm
0.8m
up to 9m
G 1/2
TABLE 1
6 Condensate Drain
6.1 Condensate Drain
A plastic drain pipe must be fitted to allow discharge of
condensate to a drain.
Condensate should, if possible, be discharged into the
internal household draining system. If this is not practical,
discharge can be made externally into the household
drainage system or a purpose designed soak away, see
diagram 6.1 for more details.
6.2 Condensate Connection
A flexible condensate connection pipe is supplied and should
be used to connect to a drain outlet pipe 22mm to 25mm OD.
non corrosive plastic . The drain outlet pipe pipe should have
a fall of at least 2.5
0
away from the boiler.
It is recommended that any external condensate drain pipe
is insulated and also preferably of 32mm diameter, to prevent
freezing in adverse weather conditions.
The condensate is discharged periodically in ‘slugs’ by
siphonic action.
It is not necessary to provide air breaks or extra traps in the
discharge pipe as there is already a trap inside the boiler.
Fitting an extra trap may cause the boiler siphon to work
incorrectly.
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