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shut-off. Close isolation valves and remove water pip-
ing from the in/out header on the heater. Drain the
heater and any piping of all water that may experience
below-freezing temperatures.
Pool/Spa Water Chemistry
Water Hardness
Water hardness is mainly due to the presence of cal-
cium and magnesium salts dissolved in the water. The
concentration of these salts is expressed in mg/l, ppm
or grains per gallon, as a measure of relative hardness
of water. Grains per gallon is the common reference
measurement used in the U.S. water heater industry.
Hardness expressed as mg/L or ppm may be divided
by 17.1 to convert to grains per gallon. Water may be
classified as very soft, slightly hard, moderately hard
or hard based on its hardness number. The salts in
water will precipitate out when the water is heated and
will cause accelerated lime and scale accumulation on
a heat transfer surface.
Raypak water heaters can operate lime/scale-free
using potable water with a hardness not exceeding 25
grains per gallon. Proper operation is achieved by set-
ting the temperature rise/water flow per the guidelines
in the installation instructions. If the hardness of the
water exceeds the maximum level of 25 grains per gal-
lon special measures must be taken to adjust flow and
temperature rise. Water should be softened to a hard-
ness level no lower than 5 grains per gallon. Water
softened as low as 0 to 1 grain per gallon may be
under-saturated with respect to calcium carbonate
resulting in water that is aggressive and corrosive.
pH of Water
pH is a measure of relative acidity, neutrality or alka-
linity. Dissolved minerals and gases affect water’s pH.
The pH scale ranges from 0 to 14. Water with a pH of
7.0 is considered neutral. Water with a pH lower than
7 is considered acidic. Water with a pH higher than 7
is considered alkaline. A neutral pH (around 7) is desir-
able for most potable water applications. Corrosion
damage and water heater failures resulting from water
pH levels of lower than 6 or higher than 8 are non-war-
rantable. The ideal pH range for water used in a
storage tank or a copper water heater system is 7.2 to
7.8.
NOTE: Chemical imbalance can cause severe
damage to your heater and associated equipment.
Total Dissolved Solids
Total dissolved solids (TDS) is the measure of all min-
erals and solids that are dissolved in the water. The
concentration of total dissolved solids is usually ex-
pressed in parts per million (ppm) as measured in a
water sample. Water with a high TDS concentration
will greatly accelerate lime and scale formation in the
hot water system. Most high TDS concentrations will
precipitate out of the water when heated. This can
generate a scale accumulation on the heat transfer
surface that will greatly reduce the service life of a
water heater. This scale accumulation can also
impede adequate flow of water and may totally block
the water passages in the tubes of the heat exchang-
er. A heat exchanger that is damaged or blocked by
lime/scale accumulation must be replaced. Failure of a
water heater due to lime scale build up on the heating
surface is non-warrantable. The manufacturer of the
water heater has no control of the water quality, espe-
cially the TDS levels in your system. Total dissolved
solids in excess of 2,500 ppm will accelerate lime and
scale formation in the heat exchanger. Heat exchang-
er failure due to total dissolved solids in excess of
2,500 ppm is a non-warrantable condition. Raypak
offers basic temperature guidelines for operation of a
potable water heater on normal to moderate levels of
hardness and solids but levels of hardness and total
dissolved solids beyond normal limits for operation will
require special setup and operation.
Gas Supply
Gas piping must have a sediment trap ahead of the
heater gas controls, and a manual shut-off valve lo-
cated outside the heater jacket. It is recommended
that a union be installed in the gas supply piping adja-
cent to the heater for servicing. A pounds-to-inches
regulator must be installed to reduce the gas supply
pressure to a maximum of 10.5 in. WC for natural gas
and 13.0 in. WC for propane gas. The regulator should
be placed a minimum distance of 10 times the pipe
diameter up-stream of the heater gas controls. Refer
to Table I for maximum pipe lengths.
NOTE: Failure of a heat exchanger due to lime
scale build-up on the heating surface, low pH or
other chemical imbalance is non-warrantable.
DANGER: Make sure the gas on which the heater
will operate is the same type as specified on the
heater’s rating plate.