35
STRATA1
3 8 & 3 8 / 4 6 C O M B I
10
0
0.5
1.0
1.5
2.0
2.5
3.0
12
14
16
18
20
10
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
12
14
16
18
20
17.6 Combi boiler hot water
system pipework pressure drop
guidance on hot water pipework pressure drop
25m
20m
15m
10m
5m
Domestic Hot Water Flow Rate Litres/minute
Flow Rate - Pressure Drop - Distance Chart For Installation Utilising all 15mm Copper Tube
A
ppr
o
ximate Pr
essur
e Dr
op - bar
For every 90° change in
direction allow 1m
Total length of
pipe, from
incoming cold
water main to
appliance and
from appliance to
hot water draw
off point
}
Domestic hot water
temperature rise 50°C
Domestic hot water
temperature rise 35°C
25m
20m
15m
10m
5m
Domestic Hot Water Flow Rate Litres/minute
Flow Rate - Pressure Drop - Distance Chart For Installation Utilising all 22mm Copper Tube
A
p
pr
o
ximate Pr
essur
e Dr
op - bar
For every 90° change in
direction allow 1m
Total length of
pipe, from
incoming cold
water main to
appliance and
from appliance to
hot water draw
off point
}
Domestic hot water
temperature rise 50°C
Domestic hot water
temperature rise 35°C
Example:
A wash hand basin is to
be served and the length
of pipe involved is 20m.
The entire installation is
in 15mm copper tube
and reference to the
graph right shows that
the pressure drop when
delivering water at a
temperature rise of 35°C
(hand hot) will be 1.5 bar.
●
Ensure adequate working water pressure and flow rate availability.
●
Consider that not only is water volume required for instantaneous production of hot water, but cold
water most likely will be required simultaneously ie: shower blending, hot and cold taps running
together, toilet flushing etc.
●
Consider that as an absolute minimum the cold water main must be capable of supplying 18
litres/minute into the property. The required working water pressure will be dependent on the length
of run to the draw off, the pipe size and any resistance at the drawoff (resistance of mixer taps,
blenders etc). Reference to the flow rate/pressure drop charts will give guidance with regards to the
hot water installation pipework (the resistance of the boiler’s water to water heat exchanger is included
in the pressure drops indicated). The additional working water pressure required for simultaneous cold
water flow can be calculated by reference to CIBSE Guide C4.
17.7 Combi boiler - domestic hot water
system design considerations