Water Chemistry - A.O. Smith 400 - 2100 Installation & Operation Manual

8
Domestic water heaters
If the temperature rise is too high, the water velocity is
too low, adjust as follows:
1. Check for restrictions in the outlet of the water heater.
2. Be sure all valves are open between the water heater and
the storage tank. Ensure that all ball valves are fully
ported.
3. Check the pump to be sure it is running properly and
that the pump motor is running in the proper
direction.
4. Check diameter and length of the piping between the
storage tank and water heater against the head capacity
of the circulating pump.
5. Be sure the pipes between the water heater and storage
tank are not less than 2 or 2 1/2 inch (63.5mm) diameter
(depending on model). To increase flow and decrease
temperature rise, increase the piping to 3 inch (76.2mm)
diameter (depending on model) to decrease head loss
in the piping to the storage tank.
6. Common manifold piping for multiple unit
installations will require larger minimum pipe sizes
and tank circulating tappings to ensure proper flow.
If the temperature rise is too low, the water velocity is too
high, adjust as follows:
1. Temperature rise can be increased by slowly closing the
field-installed ball valve in the outlet piping from the
water heater to the storage tank to achieve the proper
temperature rise.
2. Sustained high water velocity and low temperature rise
may result in pitting or erosion of the copper tubes in
the heat exchanger. This is a non-warrantable failure.
Temperature rise must be properly adjusted to achieve
the specified flow rate.
3. Once temperature rise has been properly set, return to
normal operation.
Temperature rise cannot be adjusted
CAUTION
when the burner is firing at less than
100% of rated input.
Installation & Operation Manual
(continued)

Water chemistry

Water temperature rise and maximum flow
NOTICE
data is based on heating potable water with
a hardness of 5 to 25 grains per gallon and
total dissolved solids not exceeding 350
ppm.
The required temperature rise and the standard circulating
pump are sized based on the heating of potable water with
a hardness of 5 to 25 grains per gallon and a total dissolved
solids not exceeding 350 ppm. Consult the manufacturer when
heating potable water exceeding these specifications. Heating
of high hardness and/or high total dissolved solids water may
require a larger circulating pump, an optional Cupro Nickel
heat exchanger and a revised temperature rise specification
based on the water chemistry of the water to be heated. Water
with a hardness of less than 5 grains per gallon will usually
have a pH which can be aggressive and corrosive causing non-
warrantable damage to the heater, pump, and associated piping.
Corrosion due to water chemistry generally shows up first in
the hot water system because heated water increases the rate of
corrosive chemical reactions.
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