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Finned copper tube gas boilers & water heaters – Boiler Manual
20
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Expansion Tank
An expansion tank or other means to control thermal expansion
must be installed in the water heating system if back fl ow preven-
tion devices are installed.
Cold Water Supply
Th e cold water supply must be piped to the water heater's outlet piping
between the water heater and the hot water storage tank. Th is will
prevent untempered water from entering the water heater, see the
Temperature Rise Control section below. A typical water heating
system is shown in Figure 14 and 15.
Pump Requirements
Th is low-mass water heater requires a continuous mini-mum water
fl ow for proper operation. Th e low water fl ow switch provided for this
unit will shut down the water heater if fl ow falls below the required
minimum level. Table 8B provides the heat exchanger pressure drop
chart and temperature rise table.
Th
e temperature rise across
the water heater must never exceed 35°F,
19°C
.
Temperature Rise Control
Water returned to the water heater inlet must not be less than
125°F
,
52°C
or excessive condensation of the products of combustion will
damage the water heater voiding the warranty. Th e method outlined
below can be employed to prevent this condition from occurring.
A balancing valve should be installed on the outlet side of the water
heater for purposes of adjusting the fl ow rate through the heat
exchanger. Th ermometers are installed on both the inlet and outlet
of the water heater for determining the temperature rise through the
unit. Th e proper velocity through the water heater must be maintained
in accordance with Table 8B for effi cient operation and long life. If
the temperature rise through the water heater is lower than
recommended the water velocity is too high. Premature erosion of
the heat exchanger will occur. Conversely, if the temperature rise is
higher than recommended in Table 8B the fl ow rate is too low. Scaling
and soft ening of the heat exchanger will occur.
Thermostatic Mixing Valve - Water Above 140°F,
60°C
Water can be stored at temperatures above
140°F
,
60°C
provided
that a thermostatically controlled mixing valve is used to temper
the hot water to an acceptable temperature before it's supplied for
domestic use.
Th e mixing valve MUST be set to prevent a scald injury from
occurring, see the caution against scalding above.
Storage of water for domestic use above
140°F
,
60°C
will provide
an increased quantity of tempered water and help prevent the growth
of water born bacteria.
