Cold Water Run
Cold water run differs from cold water start in that
the system water entering the heater remains below
105ºF (41ºC) continuously. Typically, this is the case
in swimming pool heating and water source heat
pump applications as well as some others. If the
system water is kept in a narrow temperature range,
a permanent manual bypass can be employed and
manually adjusted to achieve an inlet temperature of
105ºF (41ºC) or higher. An injector pump arrangement
may also be utilized to keep the heater loop at or
above 105ºF (41ºC). An injector pump approach has
the added value of being able to adjust to changes in
the system water coming back to the heater take-off.
Table G: Heater Rates of Flow and Pressure Drops
Notes: 1. Basis for minimum flow: Models 399–899, 20 gpm or 40°F ∆T. Models 989–2339, 30 gpm or 40°F ∆T.
Basis for maximum flow: Models 399–899, 90 gpm. Models 989–2339, 132 gpm.
2. Flow switch will not operate if flow is less than 20 gpm.
Temperature & Pressure Gauge
The temperature and pressure gauge is factory-mount-
ed in the in/out header.
Hydronic Heating
Pump Selection
In order to ensure proper performance of your heater
system, you must install a correctly sized pump. Ray-
pak recommends using a 20°F ∆T as design ∆T. (∆T is
the temperature difference between the inlet and outlet
water when the heater is firing at full rate). If a ∆T of
larger than 20°F is necessary, see Table G and Table
H for flow rate requirements.
Model
No.
10°F ∆T
20°F ∆T
30°F ∆T
Min. Flow
Max. Flow
gpm ∆P (ft) gpm ∆P (ft) gpm ∆P (ft) gpm ∆P (ft)
∆T
gpm ∆P (ft) ∆T
399B
67
5.5
34
1.4
22
0.6
20
0.5
34
90
10.0
7
499B
84
9.1
42
2.3
28
1.1
21
0.6
40
90
10.4
9
649B
55
4.1
36
1.8
27
1.1
40
90
10.8
12
749B
63
5.7
42
2.6
32
1.5
40
90
11.3
14
899B
76
8.3
50
3.8
38
2.2
40
90
11.7
17
989B
83
5.2
55
2.3
42
1.3
40
132
13.1
13
1259B
106
9.6
71
4.3
53
2.4
40
132
14.8
16
1529B
129
15.7
86
7.1
64
4.0
40
132
16.5
19
1799B
101
10.7
76
6.0
40
132
18.3
23
1999B
112
13.8
84
7.9
40
132
19.0
25
2069B
116
14.8
87
8.5
40
132
19.0
26
2339B
132
21.4
98
12.1
40
132
21.4
30
16
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