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IX. System Piping
Example – A 120MBH model is to be connected to a heating system as shown in Figure 9.6. A total of 20 ft of
straight pipe will be installed between the boiler and the system loop.
Count all fittings in the boiler loop (shaded in Figure 9.6):
3 90° Elbows
2 Turn in Tee (under boiler- primary-secondary tees not counted)
2 Isolation Valves
1 Y Strainer having a Cv of 30.
Note: Unions, Secondary Connection Tees, and factory supplied fittings are ignored.
Calculate total equivalent length from Table 9.4:
20 ft Straight Pipe + 3 Elbows x 2.8 + 2 Turn in Tee x 5.5 + 2 Valves x 0.6 + 1 Y Strainer x 7.0 = 40.6 Equivalent
Feet
Since the total equivalent length is less than 60 ft, flow through boiler loop meets requirements in Table 9.1
3. Indirect Water Heater Loop Piping – If an indirect water heater is used, install it as shown in Figure 9.3a or
9.3b. Refer to the indirect water heater installation manual for the proper sizing the indirect water heater loop
pump and piping.
4. Hydraulic Separators – Hydraulic separators serve the same purpose as the closely spaced tees connecting
the boiler and system loops in Figure 9.2. They also generally provide effective connection points for
automatic air elimination devices and an expansion tank. These separators are available from
several sources and may be used in place of the closely spaced tees shown in Figure 9.2, 9.3a or 9.3b.
When a hydraulic separator is used in place of the tees, the 60 ft equivalent length limitation still applies.
Select a hydraulic separator having 1" or larger boiler connections that is designed for the boiler
flow rates shown in Table 9.1.
Table 9.4: Equivalent Lengths for Selected Valves and Fittings
Fitting
90° Elbow
45° Elbow
90° Turn in Tee
Run of Tee
Gate Valve (Open)
Full Port Ball Valve
Y-Strainer*
* Based on Cv of 20. Pressure drop through strainers varies widely. 7 ft equivalent length
may be assumed for strainers having a published Cv greater than 20.
Table 9.5a: Flow Available with Boiler Loop
Equivalent Length of 30 ft or Less*
Approx. Flow
Boiler Model
(GPM)
080
100
120
150
180
* For multi-speed pumps, these tables assume pump is set to highest speed.
107672-03 - 5/18
(continued)
(May Be Used for Copper or Threaded Fittings)
Approx. Rise (°F)
7.5
19
8.3
22
9.6
22
12.9
21
12.9
25
Pipe Size
Equivalent Length (ft)
1"
1"
1"
1"
1"
1"
1"
Table 9.5b: Flow Available with Boiler Loop
Equivalent Length of 60 ft or Less *
Boiler Model
080
100
120
150
180
2.8
1.4
5.5
1.8
0.7
0.7
7.0
Approx. Flow
Approx. Rise
(GPM)
(°F)
7.3
8.0
9.2
11.9
11.9
20
23
24
23
27
77
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