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AP18733 REV. 3.2.17
49
Figure 29 – Pressure Drop through the Heat Exchanger
RECOMMENDED WATER PIPE SIZE
Number
of units
∆T = 77
°F
(25°C) ∆T = 45
°F
(7.2°C) ∆T = 35
°F
(1.6°C)
Flow Rate
(GPM)
Water
Velocity
(ft/s)
Pipe
Dia. (in)
Flow Rate
(GPM)
Flow Rate
(GPM)
Pipe
Dia. (in)
Flow Rate
(GPM)
Water
Velocity
(ft/s)
Pipe
Dia. (in)
1 5 3.75 3/4 9 3.61 1 11 4.64 1
2 10 4.22 1 18 3.21 1 1/2 23 4.13 1 1/2
Table 21 – Recommended Water Pipe Size
NOTE: The above pipe sizes are recommended based on maximum water velocity of 5 ft/s and maximum water temperature of 140°F.
▪ E. PRESSURE RELIEF VALVE
An external pressure relief valve must be installed on this water heater.
When installing, observe the following guidelines. Failure to comply with
these guidelines can result in substantial property damage, personal in-
jury, or death.
This water heater must be provided with an approved 150 psi (1,034 kPa),
¾" ASME HV Valve that must be installed on the DHW outlet line (See Figure
30). The 150 psi Pressure Relief Valve must be installed on the DHW supply
line to ensure a compliant installation and safe operation.
This water heater has a high-temperature shut-off switch built in as a stand-
ard safety feature. Therefore, a “pressure only” relief valve is required. DO
NOT operate this water heater before the supplied pressure relief valve is
installed with sufcient relieving capacity in accordance with the ASME
rating plate on the water heater.
Figure 30 – Pressure Relief Valve
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