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Water Chemistry
The required temperature rise and the standard pump sizing are
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 appliance manufacturer when heating
potable water exceeding these specifications. Heating of high
hardness and/or high total dissolved solids water will 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
low 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.
COLD WATER
SUPPLY
MIXING VALVE
HOT WATER
SUPPLY
RELIEF
VALVE
LOCK-TEMP
STORAGE
TANK
DRAIN
Figure 41 - Typical Water Heater Piping with Storage Tank
Pipe Size Requirements
Table-R, pipe sizing chart provides the minimum pipe size for
common manifold piping to ensure adequate flow.
Pipe Sizing Chart
EXPANSION TANK
(IF REQUIRED)
RELIEF
VALVE
BUILDING
RETURN
ABLE-P
Installation and
Service Manual
495,000 - 745,000
Number
of
Units
1
2
3
4
5
6
Circulating Pump
1. The water heater must be connected to a properly sized
pump that circulates water between the heater and storage
tank.
CIRCULATING
2. The pump is sized to heater input and water hardness. Care
PUMP
should be taken to size the pump correctly. See Water
Chemistry on this page.
3. The water heater is equipped with a factory-supplied pump
delay system in accordance with the requirements of the
latest edition of ASHRAE 90.1.
4. Lubricate
recommendations. Pump damage due to inadequate
lubrication is non-warrantable.
5. Standard water heaters are furnished with the following
circulating pump. Mount the pump on the unit's inlet water
connection.
495,000 -745,000 Btu/hr Models
1/4 HP, 120 VAC, 5.8 Amps
985,000 -2,065,000 Btu/hr Models
1/2 HP, 120 VAC, 7.4 Amps
This pump is sized based on installation of a single storage
tank and heater in close proximity. If the number of fittings
and straight pipe exceeds the quantities shown in this section,
a larger pump will be required.
The standard pump selection is based on the following pipe
and fittings from the unit to the storage tank:
37
TABLE - R
Pipe Sizing Chart
985,000 - 2,065,000
Common
Number
Pipe
of
Size (Min)
Units
2"
1
3"
2
3"
3
4"
4
5"
5
5"
6
the
pump
to
the
Common
Pipe
Size (Min)
2 1/2"
4"
4"
5"
6"
6"
manufacturer's
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