Finned copper tube gas boilers & water heaters – Boiler Manual
17
DOMESTIC WATER SUPPLY PIPING
Proper controls must be used to prevent water sup-
plied for domestic use from exceeding
130°F
,
54°C
or a scald injury will occur! When higher water tem-
peratures are required for appliances such as a dish-
washer, a mixing valve or some other tempering means
must be installed. Households with small children may
require water temperatures less than
120°F
,
49°C
.
Local codes must be complied with!
General Piping Requirements
Ensure that the water heater is equipped with bronze
headers.
Piping and components connected to the water heater
must be suitable for use with potable water. The water heater must
not be connected to any heating system piping or components
previously used with a non-potable water heating appliance. No
toxic chemicals, such as those used for boiler treatment, are to be
introduced into the potable water used for space heating. If a hot
water storage tank is used in the system it must be equipped with
a temperature and pressure relief valve that complies with ANSI
Z21.22 or CAN-4.4 and CAN-4.6.
The storage tank must be located as close to the water
heater as possible to prevent excessive head loss which
will reduce flow.
Water Chemistry
The required temperature rise across the water heater is based on
water having a hardness between 8 and 18 grains per gallon with
a level of dissolved solids not exceeding 350 ppm. Water having a
hardness less than 8 grains can cause excessive corrosion of the
heat exchanger. Water that has a hardness greater than 18 grains
per gallon and/or a level of dissolved solids exceeding 350 ppm
will require a recalculation of the pump size and temperature rise.
A cupro-nickel heat exchanger may also be required. The manufac-
turer should be consulted when these water conditions are
encountered. See Table 9.
The maximum allowable flow rate through a Futera III
water heater is 97 GPM, 6.1 L/s on 500 through 1000
models and 136 GPM, 8.9 L/s for 1250 through 2000
models. The cupro-nickel heat exchanger allows for
108 GPM, 6.8 L/s on 500 through 1000 models and
151 GPM, 9.5 L/s on 1250 through 2000 models, see
Table 8B.
RBI water heaters are designed to run scale free. Due to the extreme
variables of water conditions world wide it is necessary to
consider pH values and water hardness in relationship to scaling.
It is crucial to consider these two variables when making heat
exchanger and pump selections. If local water conditions are extreme,
follow the guidelines in the Heat Exchanger Selection (Table 9)
and the Pumping Performance (Table 10). Scale free operation
can be achieved by using water with a hardness between 8 and 18
and by maintaining the pH between 5 and 9. Follow the conditions
listed under NORMAL in the table. In some areas of the country
additional precautions must be observed due to unusual charac-
teristics of the local water supply. Call the nearest RBI representa-
tive for details.
To properly size the pump a grain hardness and pH test
must be taken at the installation site before the order is placed.
Proper pump sizing will improve heater performance and help
ensure heater longevity.
Expansion Tank
An expansion tank or other means to control thermal expansion
must be installed in the water heating system if back flow preven-
tion devices are installed.
Pump Requirements
This low-mass water heater requires a continuous mini-mum water
flow for proper operation. The low water flow switch provided for
this unit will shut down the water heater if flow falls below the
required minimum level. Table 10 provides the heat exchanger pres-
sure drop chart and temperature rise table.
The temperature rise
across the water heater must never exceed 35°F, 19.4°C
.
Cold Water Supply
The cold water supply must be piped to the water heater’s outlet
piping between the water heater and the hot water storage tank.
This will prevent untempered water from entering the water heater,
see the Temperature Rise Control section below. Two typical water
heating systems are shown in Figures 16 & 17.
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. The 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 flow rate through
the heat exchanger. Thermometers are installed on both the inlet
and outlet of the water heater for determining the temperature rise
through the unit.
The proper velocity through the water heater must be maintained
in accordance with Table 10 for efficient 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 10 the flow rate is too low.
Scaling and softening 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.
The mixing valve MUST be set to prevent a scald injury from
occurring, see the caution against scalding.
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.
