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This section contains specific instructions for those
units used to supply domestic hot water. All warn ings,
cau tions, notes and instructions in the gen er al
installation and service sections apply to these
instructions. Water heat ers are designed for installation
with a storage tank. The use of a properly sized pump
and the control of water velocity, as ex plained below, is
important for correct operation of your water heater.
IMPORTANT - To ensure proper velocity through the
heat exchanger, it is necessary to regulate the
tem per a ture rise across the heat exchanger from inlet to
outlet. This must be done on initial in stal la tion and
periodically rechecked. With the correct temperature
rise across the heat exchanger, you may be assured of
the proper velocity in the tubes. This will yield long life
and economical operation from your water heater.
Excessive lime build-up in the tube is a result of too
little velocity in the tubes. Excessive pit ting or erosion
in the tube is caused by too much ve loc i ty through the
tubes. Care should be taken to measure tem per a ture rise
and maintain a velocity as follows:
1. The pump must run continuously when the burners
are firing.
2. With the pump running and the water heat er off,
the inlet and outlet ther mom e ters should read the
same temperatures. If they do not, an adjustment
must be made to your final calculation.
3. Turn the water heater on and allow time for the
temperature to stabilize. Record the difference
between the inlet and outlet temperatures. This
difference will be the “tem per a ture rise.”
4. Compare the temperature rise on the heater with
the required temperature rise in Table P. Should
adjustment be needed, proceed as fol lows:
If the temperature rise is too high, the water ve loc i ty is
too low. Check the following:
1. Check for restrictions in the outlet of the wa ter
heater.
2. Be sure all valves are open between the water
heater and the tank.
3. Check the pump to be sure it is running prop er ly
and that the pump motor is running in the proper
direction.
4. Be sure the circulation pipes between the wa ter
heater and storage tank are not less than 1 1/2"
diameter for a single unit installation.
5. Common manifold piping for multiple unit in stal -
la tions will require larger minimum pipe siz es to
tank tappings to ensure proper flow. See Table Q
on page 40.
6. Multiple unit installations may also require a larger
circulating pump to achieve the specified flow
against the increased head loss of a multiple unit
com mon manifold piping.
If the temperature rise is too low, the water ve loc i ty is
too high. Adjust as follows:
1. Slowly throttle the valve on the outlet side of the
water heater until the temperature rise is steady at
the required tem per a ture rise as noted in Table P.
2. Sustained high water velocity and low tem per a ture
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.
Temperature rise is based on the hardness of the potable
water to be heated. A different temperature rise is
specified for soft water with a hardness of 0 to 7 grains
per gallon or for unsoftened water with a hardness of 8
to 25 grains per gallon. The total dissolved solids shall
not exceed 350 ppm. If there is any doubt about the
hardness or total dissolved solids content of the
water to be heated, follow the temperature
guidelines for water with 8 to 25 grains of hardness
in Table P below. The majority of all potable water
supplies will fall within the range of 8 to 25 grains of
hardness. See Water Chemistry, page 40.
39
WATER VELOCITY CONTROL
Btu/hr 0 to 7 Grains 8 to 25 Grains
Hardness Hardness
INPUT Temp. Rise
o
F Temp. Rise °F
90,000 8 5
135,000 12 7
180,000 15 10
199,999 17 11
225,000 20 12
270,000 22 15
315,000 25 17
360,000 30 20
399,999 35 22
500,000 40 28
TABLE - P
REQUIRED TEMPERATURE RISE
REQUIRED TEMPERATURE RISE