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Hydronic Heating
Pump Selection
In order to ensure proper performance of your heater
system, you must install a correctly-sized pump. Raypak
requires designing for a ∆T within the range of 16°F to
39°F (9°C to 22°C). See Table F for acceptable flow rates
for each model (∆T is the temperature difference between
the inlet and outlet water when the heater is firing at full
rate).
Feedwater Regulator
Raypak recommends that a feedwater regulator be
installed and set at 12 psi minimum pressure at the
highest point of the system. Install a check valve or back
flow device upstream of the regulator, with a manual shut-
off valve as required by local codes.
Piping
NOTE: Hot water heating systems all have unique levels
of operating diversity that must be accounted for in
the system design. The system should always include
adequate system flow in excess of the connected boiler
flow for proper operation. Where the system flow may
drop below the connected boiler flow a buffer/decoupler
may be needed. Failure to design for adequate flow (i.e.
bypasses, 3 way control valves, flow limiting balance
devices, buffer tanks, etc.) will result in boiler short-
cycling and may reduce boiler life. Always contact
your local Raypak representative for system design
assistance to avoid these issues.
All high points should be vented. A heater installed above
radiation level must be provided with a low water cut-
off device (sales order option F-10). This heater, when
used in connection with a refrigeration system, must be
installed so that the chilled medium is piped in parallel with
the heater with appropriate valves to prevent the chilled
medium from entering the heater.
20°F (11°C) ∆T
MVB
Model
GPM (lpm)
∆P
503A
44 (167)
2.8
753A
65 (246)
6.4
1003A
87 (329)
12.0
1253A
109 (413)
20.9
1503A
N/A
N/A
1753A
N/A
N/A
2003A
N/A
N/A
Notes: Basis for minimum flow is °F ∆T. Basis for maximum flow is gpm.
30°F (17°C) ∆T
39°F (22°C) ∆T
GPM (lpm)
∆P
GPM (lpm)
29 (110)
1.4
N/A
44 (167)
3.1
33 (125)
58 (220)
6.0
45 (170)
73 (276)
10.2
56 (212)
87 (329)
16.0
67 (254)
102 (386)
22.5
78 (295)
116 (439)
32.0
89 (337)
Table F.
Heater Rates of Flow and Pressure Drops
The piping system of a hot water heater connected to
heating coils located in air handling units where they
may be exposed to circulating refrigerated air, must be
equipped with flow control valves or other automatic
means to prevent gravity circulation of the heater water
during the cooling cycle. It is highly recommended that the
piping be insulated.
Minimum system flow is 115% of boiler flow.
Air-Separation/Expansion Tank
All heaters should be equipped with a properly-sized
expansion tank and air separator fitting as shown in
Figure 11.
EXPANSION TANK
Figure 11. Air-Separation/Expansion Tank
Three-Way Valves
Three-way valves intended to regulate system water
temperatures by reducing flow in the boiler should not
be used. Raypak heaters are high-recovery, low-mass
heaters which are not subject to thermal shock.
Min Flow
∆P
GPM (lpm)
∆P
N/A
25 (95)
1.1
1.9
33 (125)
1.9
3.8
45 (170)
3.8
6.5
56 (212)
6.5
10.0
67 (254)
10.0
14.0
78 (295)
14.0
19.8
89 (337)
19.8
AIR SEPARATOR
WITH BLEED VALVE
Max Flow
∆T
GPM (lpm)
∆P
°F (°C)
35 (19)
11.3
100 (379)
13.8
18.6
22.2
39 (22)
113 (428)
25.5
27.2
116 (439)
32.0
∆T
°F (°C)
9 (5)
13 (7)
15 (8)
19 (11)
23 (13)
27 (15)
30 (17)
15
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