4.5
9.0
13.5
18.0
22.5
(1)
(2)
(3)
(4)
(5)
(12)30
(8)20
(4)10
0
Water Flow litres/min (gal/min
Pressure Drop mbar (in wg)
30 RS
40 RS
50 RS
60 RS
Hydraulic Resistance Chart
For Gravity Systems - with injector washe
(16)40
(20)50
Gravity Systems
When the boiler is to be installed to an existing or new
gravity domestic hot water and pumped central heating
system, the following considerations should be given
to the design of the gravity domestic hot water flow
and return pipes.
The minimum circulating head should not be less
than 1m (3ft) with a maximum horizontal run of
3m (10ft) when using 28mm pipes. Smaller pipe
sizes and longer horizontal runs are acceptable
with suitably increased circulating heads.
The system must be designed to prevent
reverse circulation.
Pipes should be laid to maximum fall avoiding
points of possible air lock.
If the domestic hot water temperature is controlled by a
cylinder thermostat and zone valve, it is recommended
that a bypass is installed in the gravity circuit. One
method is to install a bathroom radiator, fitted with two
lock shield valves. Mechanical valves which allow the
boiler to operate when the valve is closed should not
be used.
Note: If the above conditions cannot be met, then
pumped primaries must be used.
See page 25 for wiring of boiler when installed with
gravity hot water.
Hydraulic Charts
Boiler
Bathroom Radiator used
as Gravity Circuit Bypass
when a Zone Valve is used
4.5
9.0
13.5
18.0
22.5
(1)
(2)
(3)
(4)
(5)
(12)30
(8)20
(4)10
0
Water Flow litres/min (gal/m
Pressure Drop
mbar (in wg)
30 RS
40 RS
50 RS
60 RS
Hydraulic Resistance Chart
(For Fully Pumped Systems)
11
