Boiler manual: • Installation • Start-Up • Maintenance • Parts
15Part No. 550-100-068/0308
Connect water boiler piping
(continued)
Recommended minimum pipe sizes when flow rate is
not known (see Figure 14, page page 14) (note 1)
A
B
488
3" 3"
4" 4"
5" 5"
6"
(note 2) 6" (note 2)
Note 1 Pipe sizes are based on a 20°F temperature rise through the boiler. For applications
with higher flow rates (lower temperature rise), determine the flow rate and use
Figure 15, page page 14 to size the piping.
Note 2 6-inch piping requires nipples and 5" x 6" reducing couplings (provided with 1288
through 1888 boilers only). The total pressure drop through the 1888 boiler using the
nipple and reducing coupling will not exceed ¼ PSI. For smaller boilers, the pressure
drop will be less.
ASME drain valve size
1"
1¼"
1½"
Piping multiple boilers
See 1. Figure 18. (Expansion tanks, relief valves and other accessories
are required, but omitted from the illustration for simplicity.)
The boiler piping circuits are referred to as the secondary circuits 2.
in the following.
The legend for 3. Figure 18 and boiler pump sizing recommenda-
tions follow:
Size boiler pump GPM based on the following:A
Calculate only secondary (boiler) piping circuit resistance. Al-c.
low for head loss through the boiler equal to three 90 degree
elbows of secondary pipe size.
Operate each boiler and its pump with a Weil-McLain boiler d.
control panel.
Size secondary (boiler) circuit piping using the ow rate ranges e.
given in Figure 17, page 15.
Primary pump GPM and head calculation should not include B
secondary boiler circuits. Primary pump can operate continuously
during heating season.
Connection to primary circuit — Space 12" maximum or as close C
as practical.
Check valve.D
Hand valve.E
By-pass piping for return water less than
140°F
By-pass circulator sizing:
Size system circulator as required. Determine GPM 1.
and head requirements.
Provide a by-pass circulator for EACH boiler. The ow 2.
rate for each by-pass circulator will be:
Flow = ¼ x (System circulator GPM) ÷ (# of boilers)
All circulators must run at the same time.3.
Example: For a 1,000,000 Btuh single boiler, with 4.
system temperature drop of 20°F:
System GPM = 1,000,000 ÷ 20 ÷ 500 = 100 GPM•
By-pass GPM = ¼ x 100 GPM = 25 GPM•
Determine by-pass circuit head loss for pipe size •
and fittings used.
In most applications, a standard booster pump should 5.
be adequate.
Multiple water boiler piping
