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16
DOMESTIC WATER SUPPLY PIPING
Proper controls must be used to prevent water supplied
for domestic use from exceeding 130°F, 54°C or a
scald injury will occur! When higher water temperatures
are required for appliances such as a dishwasher, a
mixing valve or some other tempering means must be
installed. Households with small children may require
water temperature 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. e 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.
e storage tank must be located as close to the water
heater as possible to prevent excessive head loss which
will reduce ow.
Bleed Air From Water Heater
Open the water heater piping bleed valves one at a time, to purge
the air trapped in the primary and secondary heat exchangers. Refer
to piping drawings (Figures 12 & 13) for bleed locations.
Water Chemistry
e 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. e manufacturer
should be consulted when these water conditions are encountered.
See Table 8.
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. 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 characteristics of the local water supply. Call the nearest RBI
representative for details.
Expansion Tank
An expansion tank or other means to control thermal expansion
must be installed in the water heating system if back ow prevention
devices are installed.
Pump Requirements
is low-mass water heater requires a continuous minimum water
ow for proper operation. e proper velocity through the water
heater must be maintained for e 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 too high, the ow rate
is too low. Scaling and so ening of the heat exchanger will occur. e
temperature rise across the primary heat exchanger must
never exceed 35°F, 19.4°C.
e factory mounted circulatory pump is sized to work
the total boiler pressure drop and an additional 30' of
pipe and 6-90° elbows.
Storage Tank Thermostatic Mixing Valve
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.
e 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.
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