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IX. System Piping
Proper operation of this boiler requires that the water flow rate through it remain within the limits shown in
Table 9.1 any time the boiler is firing. At flow rates below the minimum shown, the boiler's flow switch and/or
temperature rise limit function may prevent the boiler from firing. Flow rates through the boiler in excess of the
maximum shown in Table 9.1 can result in excessive noise or erosion damage to piping
There are two basic methods that can be used to pipe this boiler into the system. Method #1 (primary-secondary
piping) is always preferred. Additional information on hydronic system design can be found in the I=B=R Guide
RHH published by the Air-Conditioning, Heating and Refrigeration Institute (AHRI).
This method can be used in heat-only applications as shown in Figures 9.2 and 9.2a or with an indirect water
heater as shown in Figure 9.3a or 9.3b. In this system, the flow rate through the boiler ("secondary loop") is
completely independent of the flow rate through the system ("primary loop"). Use the following guidelines to
ensure that the boiler will have the required flow shown in Table 9.1 regardless of the flow in the heating system.
1. System Loop Piping - Size the system circulator and piping to obtain the design flow rate through the
heating system as you would on any other heating system. All piping between the expansion tank
and secondary connection tees must be at least 1". In order to keep the flow rates in the system and
boiler loops independent of each other, provide at least 8 diameters of straight pipe upstream of the
first tee and 4 diameters downstream of the second tee. Keep the distance between the expansion tank and
the first secondary tee as short as practical.
2. Boiler Loop Piping – All boilers are supplied with a built in circulator which will deliver the flow required by
Table 9.1 provided both of the following conditions are met:
•
All piping in the boiler loop has a nominal size of at least 1"
•
The equivalent length of all piping in the boiler loop is 60 ft or less.
To verify that the 60 ft, equivalent length is not exceeded, do the following:
a. Count all fittings in the planned boiler loop (the shaded piping in Figure 9.6). In doing so, do not
count the secondary connection tees, unions, or the fittings supplied with the boiler (these have already
been accounted for).
b. Using Table 9.4, find the equivalent lengths of all fittings in the secondary loop. Total these equivalent
lengths and add them to the total length of planned straight pipe in the secondary loop.
c. The result is the total equivalent length of the planned boiler loop. If the equivalent length calculated
in (b) is under the limit shown in Table 9.5, the boiler pump will achieve a flow rate and temperature
rise approximately equal to that shown in this table. Otherwise, the equivalent length must be reduced.
NOTICE Use of antifreeze increases boiler and system head loss and may require larger circulators.
Consult antifreeze manufacturer for proper antifreeze concentration and head loss calculation.
72
(continued)
C. Near Boiler Piping Design
Model
080
100
120
150
180
Method 1: Primary/Secondary Piping (Strongly Recommended)
Flow (GPM)
Minimum
Maximum
5.0
5.1
6.2
7.7
9.3
13.3
13.3
13.3
13.3
13.3
107672-03 - 5/18
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